Handyguy Brian had the following conversation, via instant messaging, with his lovely wife (or so he thought) about how to troubleshoot a blank thermostat, no display, issue with a thermostat and no Air Conditioning (AC). No audio here.
Some steps for troubleshooting your AC, or heat, with blank thermostat.
Below is an actual conversation. The initial assumption was bad batteries in the thermostat but we learned through troubleshooting that the particular thermostat doesn’t need batteries, read on and find out how we got the thermostat back on and the air-conditioning working. There is a surprise at the end!
Sarah: Is there a reason there is no display on the air conditioning controls? It’s hot in here and I wanted to turn it on. It’s blank.
me: probably the batteries are dead in the thermostat. The cover should just pop off and I think 2 AA batteries.
Try that first. If that doesn’t bring it back to life we can then check the electrical panel for a tripped breaker. If that’s not it there are a few other things we can easily check.
Sarah: no batteries
there r no batteries
me: you sure??
check the breaker box, there should be a breaker labeled AC or hvac or something, flip it off and then back on.
it’s probably a double breaker.
Sarah: ok brb
Sarah: nope didnt work
me: If that doesn’t do it, tell me what model number & manufacturer of thermostat we have
Sarah: i have no idea
me: It should say on the cover or something
honeywell xyzpdq123 or something
Sarah: the front says: White-Rodgers
me: okay, and a model ##?
Sarah: there isnt one on the front
me: k, hold on a min…
me: Model number should be on the inside of the front cover.
Sarah: u mean the “type #”?
me: reset the thermostat by pressing <up>, <down> buttons and move the SYSTEM switch from OFF to HEAT at the same time.
Sarah: k but we want cold air
me: please do exactly that ^^^^
Sarah: k then do i put it to cool?
me: just do that and tell me if the display comes on
me: You are pressing and holding BOTH up and down buttons while moving the switch from off to heat
Sarah: i did that and it didnt work
me: okay, do these things…..
1) Double check all the breakers, turn every one off then on…
2) check the emergency shut-off switch at the top of the basement stairs, make sure someone didn’t mess with it.
Sarah: all of them?!
me: ALL of them
Sarah: the breakers
me: all of them
one at a time
Sarah: fine then check emergency switch?
me: yes, then….
3) check the service disconnect switch, it’s mounted on the side of the main unit in the basement, it’s a normal looking switch.
Sarah: k ill start with the breakers
me: make sure no one messed with it, it should be on.
4) check the service access panel, it’s the cover that faces the red couch. There is a switch behind the cover that turns off the power if it’s removed. Make sure that cover is secure.
me: 5) In the basement, near the service disconnect switch, look for small thin wires, do they look like someone was messing with them? Maybe someone was putting something in that closet and knocked them and pulled one loose?
Sarah: what main unit?
the red switch is on i flipped and flipped all the circuit breakers one at a time so what is the main unit that has the normal looking switch
what is the main unit?
me: In the basement closet, the big beige thing
that all the ducts are connected to.
did anyone put stuff in there and maybe bumped the switch?
Sarah: ooo that thing kk brb
Sarah: nothing is in there that might have bumped it but it was off so i turned it on
me: hmmm, someone messed with it
did that fix the problem?
Sarah: yes thx u
Sarah: now the house will get cooler
me: one of the kids switched it
Sarah: y would they do that?
me: just to see what it would do
maybe they thought they would be turning on a light
A few minutes later…
Sarah: That was your daughter you were chatting with. I’ve been on the phone!
she did all that?
me: I want to make a post from the chat! Its good info
Sarah: You are funny. 😉
How about that! Handyguy Brian’s 13 year old daughter was able to fix the air conditioning!This is blog post only, no audio podcast.
245 thoughts on “No display on the thermostat and no AC”
Funny! We have those conversations with people everyday. Good thing we know so many great servicemen to help them out. Thanks for sharing!
I went through all those steps and then saw that the drain hose came unhooked from the unit and the catch basin had filled with water. After I bailed enough water out, the unit restarted.
Good catch – Just make sure the drain is not clogged and the pump is working so you don’t have the issue again.
Thank you Jay! So your post,found out I had the same problem.My A/C is back on.Predicted high for today is 93 degrees.
I followed these steps and figured out that the batteries were dead. I then had to reset the thermostat. Thank you for saving me a service call.
Y air conditioner stop working . I have a white roger s rectangle model about eigh yrs old in an condo apt . All off the sudden my unit started making nose and no air was blowing . I had a very bad burning smell coming out off my vents. I shut the brakers on an off then inside to the unit an handle with on an off I then shut that on and off . The unit still does not work . Please help
This sounds like more than a thermostat issue. I would suggest calling a AC repairman.
I have this honeywell model # CT3600A4444 thermostat and it stopped displying i tried all above steps tried to restart all circuits and changed batteries but LCD still doesnt work. When i turn that i do get the air off the vents but airconditioner outside still doesnt turn on ..any suggestion?
Either a bad thermostat, bad wire between the thermostat and AC or a bad control board in the AC. New thermostat is easy to swap out to see if that’s the issue. Return it if it doesn’t work and call a repair company.
my thermostat is not displaying the temperature just HL what does that mean?
HL probably means High Limit. It sounds like you are in a service or configuration mode. Try removing the battery (if you have one) for a minute or so then re-install. If it still says HL, try new, fresh, batteries. If that doesn’t work post the manufacturer and model number of the thermostat (Or google them) and see if you can find an owners manual to look up what may be wrong.
My thermostat was off and so was the furnace . I put in new batteries and it still did not work. I did not check breakers because I did not see how that could disconnect?
It indeed could be a breaker or fuse. Check those before calling for service.
I have a have tried all of the mentioned steps, put batteries and the display light up. Once I removed the batteries the display went blank
ok i am having aproblem with the ac. i tried to replace the batteries and when i put the lid thing back on it wouldnt fit right. while i was trying to fix it to fix it fell and the battery holder popped off. i stuck it back on. now when i try to put the lid back on two things happen. first either the light turns on and i can see the buttons if its not on correctly but the ac wont turn on, or i put it in correctly the ac turns on, but i cant see the display. please tell me what i can do as when i just make the ac work it stays stuck on 67 which is way too cold.
Wow. My thermostat also had no display on the air conditioning controls. On your advice I replaced the batteries. IT WORKED. FEELING GOOD NOW! Thank you.l
My Honeywell thermostat THM5421 had a blank screen when the water pump stopped working. The thermostat controls a 95% efficient furnace. The water pump filled up and did not empty automatically. When I manually emptied the water tank in the pump the thermostat started working again. For a permanent fix the pump had to be replaced. A furnace technician offered to replace pump for $500, but I found the identical pump on Amazon for $50 and did it myself.
Thermostat said I needed battery. Replaced them and now AC is on and when I put the thermostat to 75 it stays on 77 and no cool air coming out vents. The icon for the battery is still in the panel, not the battery pic but a circular icon.
The circular icon probably means fan. The battery icon probably indicates a full battery. It sounds like one of two issues. My first thought is you have only the fan turned on. Check if you have a switch that says Auto<>Fan or AC<>Fan, make sure its in auto or AC position. If it is, perhaps a wire became disconnected when you changed the battery. If none of those then you could have a defective thermostat or your AC has a freon leak.
If this is the first time you tried to use the AC in a while I would lean towards a Freon leak.
The house I’m renting just had both thermostats die like this overnight. I read the whole post and found a light switch in the attic that I turned off then back on and it worked. Thanks!
Thanks!! We tried all of those steps. We put batteries in our display and that came back on. Cleared water from the drip tray, AC came on. Going to have someone come look at the line, but at least we aren’t going to be in heat before they come!
If you had standing water in the drip tray that caused the AC to turn off. Check the drip tray drain line. They can get clogged. Use a pipe cleaner or bottle brush to clean that line.
Does everyone have a “main switch”… My White Rodgers 1F89-211 is not kicking on air because the unit is saying that it is 48 degrees in the house. I switched the breaker that said “AC” and it worked but just for a few minutes; then it started to drop the temperature really quickly back to 48 so the air shut off… Could that be the batteries?
It doesn’t sound like the batteries. I assume its not really 48degrees next to the thermostat. It may be due for a replacement.
I live in a condo building and the air conditioning unit is on the roof. Just yesterday, I had a AC company come out because I wanted to have a maintenance agreement with them. There was nothing wrong with my unit, this was just a check up. The AC guy said everything looked fine, but he said it needed freon and he added it to the unit (on the roof). 24 hours later my thermostat panel is not displaying. The ac was working fine until now. I have a White Rogers thermostat. As far as I can tell, it doesn’t have batteries. I check the breakers and it’s OK. Could he have left something loose on the roof? Please help. Thanks
I would call them back. Adding freon will not cause the thermostat to go out. A loose access door, improperly re-installed access door or a broken wire caused by the tech doing his thing could all contribute to the issue.
Help– I have no display on the air conditioning thermostat control — its blank? The air or heat doesn’t turn-on when I switch on/off. I flipped the AC fuses on/off at the main fuse box panel and nothing happened. I replaced the two 30amp fuses in the outside fuse box and nothing. Then out of the blue the air conditioner came on and the thermostat now displays the temperture which read 85 degrees. Please tell me what the problem could be because this happened last night and this morning around 9:30am the thermostat displayed and the air came on — do i have electrical problems or thermostat or ??? Thank you.
It could either be a bad wire, bad batteries (or battery connections) or a bad thermostat. (Or something more serious). Chnage the batteries on the thermostat and see if that helps. If the battery connections are dirty or corroded clean them with a pencil eraser and see how it goes.
First, thank you so much for taking the time replying to my situation. The thermostat I have has no batteries. We just had a whole house electrical service upgrade from 150 amps to 200 amps done about a month ago. I will go and buy a new therstat and replace the old one which all of a sudden works? Out of curiosity, after I replace the thermostat and my problem still exist, what could be the possible serious issue? I ask because as I stated, the thermostat had no display even when I pressed different buttons; in the main fuse box, the fuse wasn’t tripped but did flip it on and off; I replaced the two 30 amp fuses outside next to the outside compressor unit; and after all that, nothing. Then all of a sudden the air conditioner came on and the thermostat displayed all by itself????
Update. Hello, I want to provide a follow-up to my situation. I went ahead ad bought a new thermostat and and installed it myself which was really easy by doing two things: One, I took photo’s of my thermostat wiring; and two I had the electrical representative at Home Depot explain how to install the new thermostat using the photo of my thermostat wiring and the new thermostat Installation Instruction Booklet ensuring the wire coding I have matches the new thermostat. I installed the new thermostat and nothing other than the temperature and room temperature digits now appears on the display but the unit didn’t turn-on so I gave up and decided I’ll call a repair person in the morning. Around 3:00am my unit came on by itself and around 5:30am shut-off because it met the set temperature. About an hour later I realized it was getting warm inside the house. I looked at the thermostat that read inside house temperature 86 and air setting at 72–the air conditioner would not come on. I decided to go into the attic to see if the fuses next to the exchanger were still good good and low and behold, I noticed that the pan the exchanger was sitting in was full of water which is why I had no air–the overflow valve closed preventing the unit to work. I had the water pumped out of the pan and realized when I had the new installation sprayed in my attic and some of the installation got into the pan which clogged he drain pipe so I had the pipes blown out and now have air. Hopefully my experience will help. Thank you.
I came home to blank thermostats and no air…..googled the problem and yours was the first site I went to. I went downstairs and, sure enough, there was a switch I never saw before! I turned it on and everything just started working great! My bug guy was here this am and I am just guessing that he hit it by mistake! Thank you for going to the trouble to post this on line!! You saved me this single, female home-owner the cost of a HVAC service visit!!! And tell your wife and daughter that they rock!! : :
Can someone please be of assistance? I woke up this morning around 5am to find all my thermostats are not working with no display. My husband went upstairs and could not find anywhere to reset the box. He did go down stairs and re set it but nothing happened. It is not battery operated either. I hoping someone can help guide me through this. It is a white rogers model but I can’t see what model it is. Thanks so much. Gretchen
They lost power somewhere. Maybe a fuse in the outside disconnect (if you have that). Maybe a tripped breaker.
My ac unit was working perfectly yesterday morning. We decided to buy a Honeywell wifi digital thermostat. We followed the directions. Thermostat inside was working, but the unit outside stopped. It clicked like it wanted to start but nothing happened. We replaced that thermostat
with the old one. Still just clicking. Have no idea why its not working.
Please help. Also, it is an electric central air unit.
My first guess would be the wires to the thermostat are installed incorrectly.
Thanks Very Much!!!! There was enough information for me to trouble shoot further than I already had on my own, and we got it working again!!! It was either the (hold up and down while switching from off to heat) <which that had no immediate effect, it didn't come on. So then I opened air handler and checked the flood/backup sensor. As I'm doing that, my wife say's our 1yr old had the door open earlier and was pulling on those wires. I toyed with it. flipped the sensor on and off and examined the wire. One had 1 fray which I pushed back into wire holder, when I stood up thermostat was back on. Huge thanks for saving service call!!! Out of work at moment. thanks again!!!
2years later that saved me a service call. Master switch was switched off (looks like a light switch). Don’t know how but we do have kids in our basement all the time. You’re a lifesaver!!!
My thermostat went blank, tried to re-boot with up and down but display lo-batteries, so replaced the battery and now working fine and I stopped the service guy just 30 mts before and saved money. thanks for the post
Yesterday morning I got up to find my front door open. The AC had been working just fine. It was cycling and cooling as expected. Later we discovered the drain line had been stopped up. I got it cleared. The AC ran ok during all this. After all this, the display was gone to extremely dim. I checked everything mentioned above including the switch in the AC/heater closed and it was on. The batteries and contacts are good. No change. I have a Hunter thermostat.
There a a contact switch on the door to the bottom of the AC. Perhaps the door is not seated all the way.
Hi im having a problem. I came home one day , my house was hot .looked at thermostat and it was blank. Changed batteries and it came on . Then two days later it says low battery. I have to keep changing the batteries. What could this be
Bad batch of batteries perhaps.
I am changing batteries every two days. Buying them straight out the store. What would cause this all of a sudden. Could it be electrical?
Weird – my first thought is a bad batch of batteries. If that is ruled out I would think a new thermostat may be in order.
Oh thank you so very much. I thought for sure we fried the controller cause it was just blank.
After ready this I went outside to the heat pump and looked. Everything seems fine there.
Traced the wires back to the garage and I looked at the furnace. Hmmmm, the door was open and it has a switch . I closed the door and Poof my thermostat has power.
Go figure. Who knows, the other when I was moving my kayak i might have hit something… Leaving my with no AC for the weekend… bad husband… bad bad bad..
My A/c thermostat was blank changed batteries and display came back on. But ac wasn’t working , checked fuse box and switch on and off and changed fuse and cleaned wires in outside unit and it worked for a little bit then fan outside stopped working. Display on thermostat blinks cool on and turns on and off won’t stay on please help!
Make sure you re-installed the wired correctly. You could also have a bad thermostat. Beyond that, not sure.
Hello, I have issues with my thermostat. I replaced the batteries and screen is still blank. I switched braker switches on and off and still nothing! Do I need a new thermostat?
It is possible the thermostat went bad. Its possible the batteries (even new ones) are bad, its possible the batteries are installed wrong. It could also be something else. Double check the batteries first and if that doesn’t work then replace the thermostat. If that doesn’t work then you may need to call a Pro.
I have a Honeywell rth221b thermostat and it has been working fine but it seems to be shutting off by itself a lot. But today it turned on this morning and water started dripping in the drain pan and my son turned off the breaker. So I cleaned out the water and turned on the breaker and it has not turned back on. The batteries are good and it let’s me move the temperature up or down but nothing turns on. I switch from auto to on and still the ac doesn’t turn on. I put heat and still doesn’t do nothing. It has a wake,leave,return time and day but I don’t know how to mess with that. Can that be the problem?
Make sure the access door to the furnace is closed and installed correctly. There is a safety shutoff switch in the door.
I have honeywell thermostat unit for 2 zones – upstair and downstair. In the last 2 days, when i turn the downstair unit on and upstair one off, somehow both zones will run even i turn the upstair one off . Let me know why? . Thanks.
Has it always done this or is this a new issue?
It just happened two days ago, I never have this issue before. what cause it ?
Poor design is the cause. The unit gets clogged up too easily because its trying to use as little water as possible, unfortunately you need water to clean and rinse properly.
This is the 1st time it happened like that and i don’t know what to do. Any suggestion?
Try the suggestions in the post above ^^^
Was about to call a tech to fix this problem and came across this site. Changed out the batteries and unit fired right up. Showed my 17 year old daughter what to do if she ever runs across this problem in later in life. Saved me 125 bucks I can use on other repairs. Thanks guys.
Thanks for sharing! I was about to call an HVAC tech for our blank display until I read this and realized I’d flipped a switch in our attic and just thought it was a malfunctioning light!
The power to our thermostat has been failing intermittently for the last year or so. We have had an AC tech come in..he changed the thermostat 3 times over a couple month period. Then I asked him…could it be the wire lead to the thermostat? He now believes it is a bad common wire. He did not want to run a new wire (too much work) He wanted me to switch to the old style thermostat that does not use a common wire for power. I am planning on running a newer wire myself this weekend. Then I am questioning if it really is a bad wire? Is there a panel on the furnace that could be the cause? The power goes off for 5 mins, sometimes it goes off for a couple of hours and it has gone off for several days as well…then all of a sudden we notice it is working again. It works for weeks without a problem. Then it fails again.
I would hate to run a new wire and find out that is not the problem. Any thoughts? Thanks!!!
Wire doesn’t just go bad over time. it can go bad if a nail hits it (like when hanging a picture perhaps) or if the wire was somehow damaged (wire in basement being used as place to hang hangers). You would replace the wire without fishing it through the walls as a test. Just run a new wire to a convenient spot a couple feet away and see if that solves it.
Help >< Last night our control panel (Honeywell no #s or I'm not sure where to find the serial number at) went out, I replaced the batteries and it came back on, but the heat never switched on. It's a brisk 66 inside our house with a 20mon old baby. Our a/c unit is on the roof of the house and I only see the hot water heater in the laundry room. I also checked the breaker box and manually tripped the breaker off/on to see if it needed a reset. At this point my husband and I have no idea, but it's definately colder inside my house.
Our family has a Trane Z-Wave thermostat, model # TZEMT400BB32MAA, which stopped displaying a few days ago. We have 2 air handlers in our home, one downstairs and one upstairs, and the one upstairs is working fine. My husband switched the covers and both panels display upstairs, but not downstairs. We have tried turning on and off the breaker from the breaker box, as well as the emergency shut off switch on the air handler, but nothing. Is there anything else we can do before calling an AC pro or an electrician?
Make sure the door to the air handler is properly closed plus the steps in the post above. If nothing, then call a pro
It still is not coming on. Thank you for your assistance.
Hi Mimi – We have the same exact issue. What did you all o to resolve it?
Thanks for this post. I’d done all but the last on my own then came across this and discovered the switch conveniently located where little people can easily reach and that was the problem!
Hi: I reset my thermostat (1F866-244) because I thought my problem was the thermostat, but it changed my system from Celsius to Fahrenheit. How can I set it back to Celsius? – Thank you
Not sure, try contacting them http://www.emersonclimate.com/en-us/resources/Pages/technical_support.aspx
My A/C won’t work… No display at all… My thermostat is robertshaw 9520
Try the above checks ^^^
Hi:) Do you know why my heat would run all night when the battery on the thermostat died? If the panel is blank, does that mean the system can’t follow the program? I have a White Rodgers 1F80-51. Woke up and my house was 84 degrees, the program was set to 70! Any help would be appreciated.
Correct, if the battery dies it will not follow the programing.
What is that switch knob for on the inside of the thermostat?
No idea, all models are different.
Had blue light on thermostat but no numbers – changed batteries. Now have no lights or digits showing , but can make fan come on with switch – Does it sound like the thermostat?
Cant say for sure without looking at your particular thermostats owners manual. Check all the steps in the post above. You could try a new thermostat and if that doesn’t resolve your issue, return it, and call a repairman.
tried installing a new Wi-Fi Thermostat from Honeywell. My current Carrier thermostat worked fine. Once I uninstalled it and connected all the required wires to the new unit I realized that I forgot to turn of my breakers to both the AC and to the Furnace! Finished installing the new unit and I wasn’t getting any power to my new thermostat. Then I uninstalled the new unit and reinstalled my old one and now I am not getting any power to my old unit. Could I have have blown a fuse? I beleive my unit is in the attic. Is there anything else you think I should check?
Double check the obvious stuff first. Make sure all the breakers are on, cycle them off then on again. Where else did you work? Did you open any access doors the the furnace? Make sure they are closed properly.
I’ve got a problem with my AC in my rental townhouse. During the day – around 7 a.m., my AC will start working. Sometime in the overnight hours, it stops working.. usually notice around midnight. My thermostat is set for 73 but it’s 75 in the house. Right now, it’s humid and my neighbors is still running.
What could be the possible issue? Thanks for the help.
Does it run but not cool or does it shut off? if it shuts off, I would check to see if you have a thermostat with timers set incorrectly. If it is running but not cooling I would suspect low freon.
It shuts off completely… initially I didn’t notice this but the last couple of times it did it, I had a pool of water around my unit.. I’m starting to suspect that something is freezing up and, after awhile, thaws out and starts working again. I do know it’s a bit low on the freon but the maintenance man said the landlord doesn’t want to pay for the fueling up.. (go figure!)
Thank you for documenting this conversation. I was able to resolve our AC/thermostat problem by reading the first few sentences. I snapped off the thermostat cover(swing out from the bottom) and replaced the 2 AA battteries. We didn’t even know there were batteries in the thermostat. Those old batteries must’ve been in there for YEARS! Thanks again!
my thermostat won’t display temp. the furnace blows but air or heat won’t turn on..i changed the batteries..still dont work
Try a different set of batteries and make sure they are in correctly. if you know bateries are good, check some of the things in the post above ^^
Someone turned off the unit in the attic
Thank you for you help
HELP!!! My thermostat (Honeywell RTH221B) led is blank. The ac turn on but we can’t keep it on for more than 1 hour cause it starts to freeze up. It doesn’t shut off so once the house is cooled. (It have a strange sound like air leaking from a tire.) I turn it off and don’t turn it back on until the next day. Please help me figure out what’s going on. Thanks
Make sure you have fresh batteries. Read the article above for possible things to check. Make sure the door to your furnace is closed properly. Also, check your furnace filter. The LED blank issue may not be related to the to freezing up issue.
Thanks for this page! I also had problems with my thermostat and literally Googled “AC thermostat doesn’t work.” I didn’t know it even had batteries but that’s all it took to get the display up and working. I feel so empowered, LOL.
Hello, I’ve got an a/c prob the thermostat quit working totally it’s a robertshaw 9520 I know it don’t have batteries, and a heating/ air guy I know said to change the blue fuse 3m but I only see a clear hollow tube fuse is that the one I’m suppose to change?
Is it possible to replace the part of the thermostat the snaps off the wall without messing with the wiring. I have a Pro1 -T 801.
I just looked at the manual
I’m assuming by your question that the display is somehow faulty and you have narrowed down the issue to the thermostat itself. I would think you could buy the exact same thermostat and replace just the display. (See page 9 of the manual)
Hi, We have robertshaw 9400 thermostat which went blank today. I changed batteries and it started displaying number for couple of seconds before it went blank again. When I tried resetting it, it started displaying for few seconds then went blank. When i put it on cool mode, A/C is running. Not sure what is the issue with display/thermostat.
Sam, that is weird. I would make sure the batteries are fresh. If they are, I would look at the battery terminals to make sure they are not corroded. Use a pencil eraser to clean them if they look rusty or dark. Your manual is here http://www.robertshawtstats.com/spaw2/SiteContent/9400%20Thermostat%20manual_110-1039.pdf Check the other troubleshooting steps. Their phone number is in the manual, perhaps a call to them. Other than that, maybe its time for a new thermostat.
i have a old thermostat that has the mercury in it. it will not turn on what so ever. we have checked all the breakers and everything on the furnace and all the wires and it still is not working. the lights do not come on or nothing. i have four babies. do you think it could be the thermostat or am i going to have to call a tech to come out. it is a cooling system with a heat pump.
You may need to replace the thermostat or have a tech out. One last thing to check, make sure the furnace door is properly closed. They have a safety switch on them that needs to be engaged.
I have a BesTech BT110D Thermostat. “LO BAT” appeared on the screen.
2 new batteries (exp. 2016) were installed. (Unlikely that thermostat was switched to OFF beforehand – as suggested in the manual). Now there are no temp readings at all. Screen is blank. Cooling stays on (to 62 degrees now) unless switch is moved to off position. Unable to change temp up or down. Fan stays on all the time even when on “auto.”
Are the batteries installed correctly? Does this seem to be how it operates with no batteries?
I checked all of the fuses in the blower air handler unit and they were fine, and then I noticed that the condensate pump was running full time, and wondered why. The clear tube was very full, but was not emptying outside as it should.
I found out that the end was blocked by crusty buildup on the outside of the the house, and the condensate pump had a limit switch in it, that prevented the unit from turning on the thermostat power if the condensate pump was full.
Cleared the blockage of crusty stuff on the end of the pipe outside, two stories up, and shazam, the thing is working again! LCD display came back on and the condenser started.
Thanks to good installation guys for putting that switch in there, otherwise when the condensate pump overflowed it would have caused water damage!
We have a Trane XT302C. There was a power outage in the neighborhood earlier that lasted 30 mins or so, and now the thermostat display is blank. We’ve checked all the fuses – they are fine. Can’t see any “reset” type of info in the manual. No batteries used in this thermostat unit. TIY
Try flipping breakers off/on.
I followed all the instructions above and still there’s no display on the thermostat.
Perhaps its just gone bad.
Thank god for this thread. My lovely husband and I just moved into a new house. He “accidentally” turned the emergency switch off and we had no ac all night! ! Once I got to that part in your thread I jumped up and poof, fixed!
i have a problem. i changed my thermostat out about a week ago and ever since then my ac wont shut off even when it reaches set temp. and the tstat reads different than what is actually blowing out of the vents. i have actually changed out the batteries several times and exchanged the tstats at the the store thinking it was faulty, but still no luck.
Not sure, perhaps its not wired correctly or an incompatible model. I would double check the wire connections and if they are correct then perhaps try a different make/model thermostat.
Noticed the thermostat was blank & will not turn on. Honeywell T8001. Flipped breakers & checked fuses & everything is good. Had Direct TV installed yesterday & they had to run the wires through the attic. Could the have caused the problem?
Problem solved Direct Tv flipped the switch off !!
I went through all the steps and found a switch under the thermostat .i pushed it to the right. My thermostat lit up and I have air condition.!!!!!!!!!!!!!! The switch somehow went to the left shutting off my thermostat. Thank you!
The thermo went blank , had tried all the breaker / fuse checks then remembered that you had saved me a year ago . Had link bookmarked ( sorted through a thousand & found it ) . Looked for switch in handler -still can’t find it ( amana ). Then saw the drain mentioned !!! I’m an idiot but you are genius – drain pump box had filled up . We had 10 inches of rain – handler must be working double time . Thank you all
My White Rogers thermostat, Type 1f88-290 shows to dashes instead of the temperature. Furnace sounds like it is running but the condenser/fan outside is not running. Low volume of air is blowing from the vents. Any ideas?
I exhausted my ideas in the conversation above ^^^
The water drain line is clogged.
Condensation water backed up into the pan beneath the air handler, throwing the safety switch which prevent s water overflowing the pan and ruining your ceiling.
Look at the pan.
Full of water?
Then that is the only problem.
Usually the blockage is at the end of the drain outdoors. You should have been putting some bleach into the line once a year to prevent this.
Hi. I made a big mistake. A roach crawled behind my control breaker so I sprayed behind it. Now the control panel is blank. It gradually went blank. There are no batteries. It is a Bass model #P747-1000. Thanks!
Thank you thank you thank you for having this complete dialogue of directions on line! With my help, my husband actually found the problem with the emergency switch.
This made my morning!
HELP!!! We have an ac unit in our apartment that keeps rebooting itself. I have yet to figure out if there is a pattern but it will go completely out (blank display) and when it comes back on, assuming I am home, I have to lower the temperature because it resets itself to 85 degrees. The apartment maintenance and management team have said nothing is wrong because every time they come in it is on. Finally I was able to show them the ‘blank’ box so they replaced the batteries. That didn’t work, then they replaced the box, that didn’t work. Then they said they replaced a transformer. That didn’t work. I am beyond annoyed! I have a dog at home and if we aren’t there to lower the temperature when it does come back on, it gets really hot in the apartment. ANY ideas. Sadly this same thing happened in a previous unit we were in, among many other problems, so we relocated within the building. That time, they determined that birds were messing with the wires on the roof. They have said everything looks fine there so I am at a loss. I’m convinced that its faulty wiring somewhere but how do I prove it?
Thank you handyman AND your 13 year old daughter. MY 13 year old daughter came downstairs to tell me the thermostat was blank screened and it was hot upstairs. This message helped me fix it. Thanks!!
My digital thermostat went blank. As did my AC. It doesn’t require batteries so I flipped the breakers, checked the outside unit, can not figure out why it went blank and stopped turning on. I read all of the above and unless I am missing the main switch, which I haven’t found one then I’m just asking if there’s anything else to be done? It’s a totaline thermostat, and only a couple years old. (I live in Florida so no basement, where else would the main switch be?)
Thanks in advance!
I have a white Rogers thermostat. No batteries. The thermostat keeps going blank and air shuts off. After awhile I am able to run the air and it cools fine but then after about 30 minutes it shuts off again…please help…this Florida heat is too much with no A/c thanks
My drain pump seems to be functioning
I have a Pro thermostat which is not dependent upon batteries. It went blank after a lightening storm on our property. I checked the breakers and none were tripped. Any ideas?
I saw where the guy said to make sure the cover was secure. Ours wasn’t, and that fixed the problem! Just as i was about to spend who knows how much for a service call. Thank you!
Thanks, i tried that and the cover was secure, but still no power.
My white rodgers does take batteries put new in i have left side display saying 60 right saying nothing fan will turn on when switched to on but air will not come on
I have 2 identical units, one for upstair and one for down.
Carrier FB4ANF024, Tis model number also show as a Bryant and a couple of other brands.
My downstairs thermostat is blank an the unit will not function,
I took swapped the Thermostat mother boards and the downstairsw unit that is blank works when moved upstairs.
I have gone into the crawlspace and checked the fuse, aqnd the condensation tube. Both are good. Breakers are reset and good One for AC and one for heat.
I have changed my thermostat to a smart one. Touchscreen, wifi, Honeywell. I am not getting power to the new thermostat, but when wires are probed they say they’re live. Put old thermostat on and that will not power on again. Of course following protocol and instructions, turning off the AC switch at the panel and then on when installed. Checked furnace and it looks as if it is not getting power as well. Where do you think I should go from here?
make sure the access door to the furnace is properly closed. make sure all wiring is correct.
We found it… I’m sorry… A fuse blew on the furnace. It was untracable and we just happened to check. It works now. Thanks. Love your blog
Did all the steps in here but thermostat is not coming on. Check the drain is not clog. Check the main breaker turn them all off and back on one by one and nothing. My thermostat has no batteries, took it out check all the cables in the panel everything is where supposed to be and nothing. Is cooler out side that what it is in side the house 🙁 . C an someone help please??
Is the access door closed properly? Its a silly thing but I have seen it trip up many people.
My Honeywell thermostat has a blank screen. I switched the batteries because it was blinking low battery. Now the screen will not come back on. My concern is that I won’t be able to adjust the temp?! I have no clue about any fuses or other switches. The unit is on and running so I guess I’m fine??
It could be bad batteries or they are in wrong. I assume you didnt change any wires. You need to get good batteries installed correctly.
Thank you handy guys. It was cold in my house. Had to go up to the attic.
Hi, My thermostat is Trane comfortlink II. my A/C or heat not working. Thermostat has a red light and ( ERR 91) flashing. Doesn’t use batteries.
1-I removed it and reinserted again from the wall.
2-I turned off/on the attic switch.
3-Flipped breakers off/on.
still the thermostat will not respond to change it to cooling ON.
I have no A/C or heat coming. Outside unit or furnace not running.
Thats a communication error. Try everything in the above post, all of that is free and wont take long. If none of that works then you may have a bad thermostat, bad wire or bad connection.
It is now becoming cold in the house . we changed the filter and went to t0 turn up the furnistate. There at no lights or numbers on the screen.
Try the troubleshooting steps in the post above. If it doesn’t work then call a repairman.
The exact same situation (as in the Chat with the kid) happened to me and I followed their conversation and just fixed MY unit too! I’m happy to say I’m as smart as a 13 year old!
Thank you for your chat post!
I have White Rodgers thermostat. The display is working but I lowered the temp because we had company, now it won’t let me raise the temp back up. The “cooler” button works, but not the “warmer” button. Any suggestions?
It sounds defective, I would replace it.
Hi I’m having a problem with my thermostat saying low battery. The battery dies in couple days after replacing a new one… What could be the issue ?
Bad batch of batteries perhaps.
just replace old thermostat with honeywell 5-2 dayprogrammable. two of them work flip between normal and abnormal. can somebody have solution
I reads have a white rodgers Model #1F78 and the Left side 08 degrees while the right side reads 62 degrees I have three grandchildren and its getting cold please help
Nevermind figured it out only uses energier batteries only no off brand batteries
This was not only great advice but truly charming to read! My thermostat had a blank display. I changed the batteries and still nothing. I checked the breakers (all of them) NOTHING. I tried new batteries. While doing so I noticed that the batteries fit loosely. I took them out and noticed that the metal contact was pushed in. I used a dental tool to pull it back into place. Replaced the batteries and Voila it worked. Just FYI, my thermostat says you must turn it off when replacing the batteries.
We are having a issue our white rogers is blank the heat is on but not shutting off.
Check the things mentioned above and in the comments. Maybe its a bad thermostat.
My thermostat fell of the wall and came apart in pieces. I managed to put it together and place it on the wall. Only a green light pops you . The air vent cut on but can only produse cod air, I’m freezing but it’s snowing out here , what do I do
Get a new thermostat.
Hello. I have a white Rodgers Mercury thermostat. Heat not working. Took thermostat cover off and the Mercury will be tipped to the left, so it should come on. If I throw the furnace breaker (sometimes more than once) it will come on. It may work fine all day but it’s a daily routine to throw that breaker. Is it time to replace my thermostat? Or is it something electrical? Thanks
I’m not sure what it could be. Those merc thermostats are pretty simple devices and I cant imagine flipping the breaker would have any effect on one. Its more likely the issue is not with the thermostat. That said, they aren’t very expensive if you want to try a swap.
Thanks for your reply!!
Totaline Thermostat P374-1800 has no display. It is not battery operated but hard wired electrically. The furnace fan seemed to be blowing cold air. We turned off the breaker and this then turned off the fan when we did this last night. We then turned the breaker back on 15 minutes later and the fan didn’t turn on at that time, but just now, about 18 hrs later, the fan is blowing again. We are being told that we have a bad breaker and that this needs to be replaced. Could you explain why the fan could be blowing if the breaker is bad? or does this fan work off of some other system? And do you agree it could be a bad breaker and will this bring back the Thermostat Display. Thanks.
We just returned to the house last night after being away 3 months. So we do not know when this first occurred, since we had the thermostat set on Program Mode to run when it would get below 55 degrees (furnace) or above 85 degrees (AC). We are now needing the heat to work.
Its hard to say – if you have electric heat then you would have several breakers. If you have AC you have a couple more breakers. I have heard of breakers going bad but I have never actually seen it. i don’t think its that common. try every step in the above post. make sure you didnt miss anything.
We lost power and when the electric company finally got us power the thermostat is blank. Any suggestions?
Follow the troubleshooting steps above. if nothing, then call a pro.
Hi…I have a Aprilaire 8363 thermostat. Just this morning, the display was blinking with several types of numbers, etc. I replaced the batteries, but the all of the blinking is still happening. I cannot set my day, time and temp. Any ideas on how to fix? Thanks!
Not sure. I would double check the batteries are installed correctly and are fresh. Check the things in the above post. All else fails contact them http://www.aprilaire.com/about-aprilaire/contact-us-at-aprilaire
OMG, thank you sooooo much. I feel like a dork. Its 82 in here (Florida) and no A/C. So before getting the repair person in, checked the breaker and checked the thermostat for batteries…no dice. Then I looked up and followed your steps …well, earlier this morning I had put vinegar in the A/C unit as I was told to do, but tried to turn on the light in the A/C cubbie, and accidentally flicked OFF the service disconnect switch. THANK YOU sooo much for an easy and logical fix, and for saving the cost (and embarrassment) of having a repair person in to flick a switch !!!!
My thermostat went blank and I can’t get my air to cut back on.
Try the suggestions in the post above before calling a repair man.
I have a Honeywell Wi-fi thermostat RTH9580 model. Screen went blank and there is no heat or ac. Checked switch and breakers and all were set properly (not tripped or off). Replaced thermostat and it did not power on. Furnace is Lennox Elite Series. When I switch furnace circuit breaker off and then back on you I hear it cutting on for a couple of seconds and it then shuts down. What do I do?
Try the suggestions in the post above. Perhaps an emergency shutoff switch? Maybe the blower access door is ajar? Maybe a wire has been accidentally cut or a control board inside the main unit has failed. Try the easy stuff first ^^^
Reading the threads great information. My problem is there is no display with a black mark in the center of the display. Replaced the batteries i also reset the breaker. Still no functioning display. The furnace and ac fo turn on and work, just cant what is set at or the temperature
The model is 1f78 non pgm the outside is stamped with Emerson any feedback is helpful
Thank you. After reading the handy guys reply, we replaced the batteries and the thermostat reset. Thanks again handy guys.
My thermostat displays the temp I can switch it to heat and the displays shows the fire symbol and wht temp I have it set to. Then if I try and turn on the ac only display is the actual temp the snowflake or the setting for the ac doesn’t come on. Then when it finally does come on the system starts and works then shuts right off……please help me
Hmmm, very weird. A previous commenter found their drain pan full of water. maybe check that if you have tried everything else in the post above. Maybe its time for a repair person.
Hi my thermostat is blank it doesnt have batteries and i have checked the breaker box
Its an emerson thermostat
The house we are buying just had a new thermostat put in Feb 2016 it is a pro1 T701. My thermostat is blank the fan part works and every now n then I can keep hitting reset to get it to work for lil bit. What can be causing this? We have replaced batteries and when on the mount the blue light comes on and stays on but screen stays blank. So I can’t turn a.c. on or heat on and it’s 90 degrees here.
Thank you for all your posting!
I had a thermostat: Honeywell TH4110D1007 that was black screen.
I check most of the troubleshooting above.
Finally this morning I find the solution online that fixing the issue.
The safety switch that put on the side of the water pan was triggered.
That water was 2/3 of the pan so the switch was shut off.
Drain out all water from the pan and my thermostat is back on.
Source: “Central Air Stopped working, Thermostat went blank?”
My troubleshooting for thermostat battery:
My thermostat has EMPTY spot to put 2AA battery. This setup uses direct DC from transformer so that no need to add battery.
I tried to add 2AA battery. The program was on but not trigger the air conditioning. So if you have same issue just by pass this step.
Hope you can fix yours too!
Ahhh yes, those pans SHOULD have a drain on them but those drains can get clogged up with mineral deposits causing them to over fill or even overflow.
We did everything above.
We also switched out the thermostat from the downstairs unit that is working and that didn’t work either.
Sounds like a bad connection or bad wire somewhere.
Got home to bite and both my thermostats were off and no AC, they are actually powered and are Honeywell TH7000. Can you help before I call for service? Thanks
Try the steps outlined in the article first.
Hey, I had my central air working yesterday for a few hours during the heat of the day. Later I passed by and the LO for the battery was on the screen so I changed the batteries. After that it wouldn’t work. What the hell? So this morning I went and bought brand new batteries, switched them out and it still won’t work. Got the display and everything but no a/c. Can you help me?
Try the above steps and maybe a few of the suggestions in the comments. If you checked all of those things the its time to call a repairman.
Hey, the model number of my Honeywell thermostat is T7512 A 10334, there in no display and I installed new batteries, the ac is not functioning because of this, please help, Thanks!
Okay, did you do all the other things mentioned in the post above? ^^^^ If you did, call a service person.
Just followed your steps after switching the breakers off one by one then turning them back on I have lost power to a few rooms in my house and still no AC
Got power back in those rooms one of the breakers wasn’t working correctly but still no power to thermostat and ac unit still not turning on
Awesome A/C troubleshooting tips delivered in a unique way! I thought a storm blew out the A/C. Followed your text story and fixed the problem. Condensation in tray… Mopped it up, A/C turned on, smile on face. Thank you!
It wasn’t a contrived post. It really was an online chat the Handyguy had with his daughter.
Hi everyone please i need your help if any one knows do let me know my thermostat went blank blue its not cooling anymore
the model is : S-Th-1289-3L11(xf)-bs-mm
please help my mail *[email protected]*
I have a Gemtech unit and replaced the batteries but now it won’t turn on, how can I fix it?
Thanks for this, you saved us a load of time, money and aggravation! My thermostat display was blank and I did the reset steps and not only did the display come back so did the AC!!!
My AC is set at 73 and when the temp reaches 73 it goes off. Yet 10 minutes later it goes right back on. It’s 90 degrees outside. Why is it doing this???
I would guess its doing exactly what its supposed to do. You may have a lot of heat gain I suspect and you loose any cooling very quickly. I would look at increasing insulation (in the attic is easiest), caulking windows and using drapes or blinds to cut down on the sun coming in.
We have been doing that.. Keep our blinds close. We live in a 3 floor townhouse. We have 1 unit on the 2 nd floor out basement gets freezing. We don’t know what to do. It containly runs!!!
It sounds like you have leaky ducts perhaps. All the air is leaking into the basement. Maybe look into duct sealing.
https://www.energystar.gov/index.cfm?c=home_improvement.hm_improvement_ducts A pro can do it with a spray to seal what you cant see.
Something in the system is causing thermostats to quit working. I’ve bought two new ones in two months. Currently running a BesTech BT11NP that was installed two weeks ago by a repairman. Now it has problems too. It worked fine for about 10 days after he installed it, but then it stopped working. The entire LCD display was blinking. I replaced the batteries, no change. I pressed buttons, no change on the down temp button, but the up temp button flashed a 3 followed by a 10, then resumed the all blinking mode. I called the repairman (Saturday evening), and he talked me through a hard reset of the thermostat. Removed the batteries, removed the thermostat from the base, and waited for the display to clear. Replaced the batteries, put the thermostat back on the base and reset the temperature. It worked! For 3 days at least. Last night it did the blinking display thing again, so I did another hard reset. No joy. I called him again, he suggested leaving the thermostat off the base with batteries in it. It continued blinking for about an hour, then displayed a steady 79. I put it back on the base, and it has been working since then.
My question is, what in the system would cause 3 thermostats to go crazy in two months?
John – I would just pursue (as you are doing) warranty service on the new thermostat and work with that tech until the issue is resolved.
I have a HONEYWELL thermostat. The a/couple inside unit comes on. But the outside was not. I changed the batteries. I think it might be OK? Hoping. Would this be the answer? Batteries?
Not likely the batteries.
Our home thermostat came apart approx. in middle and I have not been able to get elec pins and plastic notches aligned so the front half fits on the back. Seems it should be simple. (Honeywell T862402004}. How to fit together again.
You guys rock! Thank you for posting this information. I didn’t realize until a day later that it was actually a conversation between father and daughter; that’s hilarious. After sitting in a hot house all day I finally decided to Google search blank thermostats and your post came up. I didn’t get past check batteries before I went running to replace them and sure enough that’s all we needed, thank God. I really appreciate you sharing this information and helping us troubleshoot.
My ac is not working and the thermostat will not read the temperature that’s in the room but it shows the temperature you want to set it on…what could it be? I already put brand new batteries in it and checked all the breakers and still not working.
Could be a faulty thermostat or something specific to that model. I would google search for a user manual and start there.
For past few months, my A/C doesn’t seem to be working properly. I had an old thermostat initially, even i had turned it to cool or heat, there were no cool or heat air coming, however the fan seems to be running continuously. I thought, there is a problem with thermostat and replaced with new Nest. It ran fine for few days, but recently experiencing the same issue. Nest thermostat shows the issue as “No power to Rh wire”. This is happening on and off. I called up A/C repair guy and unfortunately the A/C was working whenever he shows up and can’t replicate the issue. I’m trying to resolve or find where and why it is happening. Any inputs will be highly appreciated.
I don’t see that code listed on Nest’s website https://nest.com/support/article/What-do-Nest-s-error-codes-mean If indeed its a broken wire then look into replacement.
Had the same problem and couldn’t figure it out. After reading this I checked the emergency switch and found it was off. Now, next project is the interrogation of my 3 and 5 yo boys to see who was the culprit!! Thanks for the Good information!
We been in our new home for a month now and we have a totalline thermostat im assuming its old (probably built with the house) & came home from work it was off. The only buttons it have is fan, mode, up & down arrow! Somebody please help me fix this without calling a technician out here.
Check the this written up there ^^^ if nothing helps then you have to call.
Hi. I’ve got a Honeywell non-battery, non-programmable thermostat (number inside on a decal says T8400C 1008 (2)), and it’s getting harder to get the up and down buttons to respond when pushed so that I can change the temperature setting. I.e. when I press and hold either button, the temperature setting doesn’t always change very fast, or at all.
I took the thermostat apart and put some rubbing alcohol on a swab and rubbed it on the black, rubbery back of the button and also on the area it presses on the circuit board, which seemed to help for a week or two, but now the buttons aren’t responding very well again. I have to hold them a long time or press them harder to get the setting to change.
Any ideas on how to get this working better?
Everything else on the thermostat (display, slider switches, etc.) works great and once I finally set the temperature, the system gets the area to that temperature.
Cleaning those contacts is the only thing I can think of. Try cleaning them with a pencil eraser. If that doesn’t work then perhaps its time for a new thermostat >>> http://amzn.to/2g2uEFa
OMG!!! We just purchased a house and it has been interesting so far to say the least. Our A.C. display wouldn’t come on. I checked the battery part and put some in. The display came on but still the unit wouldn’t come on. I couldn’t flip the breakers yet because my husband was still working (he works from home). Me being the wife I am decided to Google our issue and your article came up. Just when I was almost tired of reading I saw the part about the emergency switch looking like a regular light switch……..earlier I was in the garage and flipped what I thought was a light switch in our storage closet…..as soon as I went back and flipped it the A.C. came on!! The switch is on the ceiling which is odd and I know now there may have been a reason for that. Now if I can just find the light switch that goes to the LIGHT in the storage closet we’ll be ok. Thanks for the AMAZING article!!! You guys are a life saver!!
My thermostat is blank. I tried holding the two buttons and turning it on and nothing. I don’t have a circuit breaker in my breaker box for the heating/ac. I don’t know where the emergency shut-off switch is. I can’t find one. There are two I guess breakers in the closet with the unit. I pulled out the on/off handle and there are two copper pieces but no circuit breaker or fuses. I looked outside and found another box with the same thing. It just has a thing that you pull out to shut it off. It has two copper pieces in it. I can find no switches in the garage or outside to turn it on/off. I looked in the drain and it is not full. I don’t know where my “drain pan” would be to check it. I live in a two story house with the AC/Heating unit upstairs and the thermostat downstairs. Help! Where is my shutoff switch, circuit breaker, or drain pan?
My emergency shutoff is at the top of the stairs leading to the basement. My breaker box is in my basement. My drain pan is right below the AC coil in the HVAC unit in my basement. Look in those places then perhaps its time to call a pro.
Hi my ac lennox model 51M32 it just stop workinh n not displaying anything on the screen. I have turned off the breaker on both ends and still nothing please help.
Have you tried/checked the other things in this article? if so, it may e time to call Pro or replace the thermostat.
Hi.. I have a DICHO thermostat. A couple days ago, I walked by and noticed that the word FILTER was on the lower left bottom of unit. And it was time to change the furnace filter, so I did. My air works great, my heat works great… I cannot get the word Filter off the display! Any clues???
I’m not familiar with that brand of thermostat. There should be a way, from the thermostat most likely, to reset the filter reminder. Have the manual anywhere?
Was wondering…on my most basic non-battery digital Carrier thermostat. Whenever I go to adjust it in AC mode I push arrow down/up and the screen comes up reading “1”…if I arrow up it goes all the way up to “13” …and goofing around found that it can even go into negative numbers. However…my problem still exists. The air wont come on and when I push fan power nothing happens either. Can even get the fan to come on. I have checked the disconnect outside as well as the breaker in the house panelbox. What gives?
Check the other things in the post above ^^^.
I did everything you said with a Simple Comfort AS7840. I have two thermostats in my home. The one downstairs works perfectly fine and the one upstairs isn’t working at all. They don’t operate off of batteries but off the electricity. I reset the brakers and made sure everything was connected. Still no dice. Any advice would be appreciated since I’m renting the home and the maintenance guys never got back to me.
It could be just a bad thermostat or bad/broken wire somewhere.
I have a Robert shaw thermostat and all of a sudden the house started to warm up so I checked the thermostat and before this when the air was running there would be a green light on the thermostat and now there isn’t any lights and there is very little air coming out of the vents.the unit will run when turned on just not blowing that much air.the thermostat doesn’t have batteries so what should I do?
I would STILL check the items in the post above. Additionally, I would check the furnace filters to make sure they are clean and not clogged. Good luck.
I cut the thermostat on cold. House would start to get cool then notice it started getting hotter in house. Walk to thermostat, the green led light was off and display was off. Checked breaker nothing was tripped. Went to the thermostat and flipped it back on and display lights and a/c came back on.
Next day……. same thing happened! Ac and display was off But I forgot to cut the thermostat off from cold. I noticed it was hot before but now it’s cool in the house and I haven’t touched the thermostat. The display and ac just started cutting on and off when it wants too. No batteries
Hmmm – faulty thermostat maybe. faulty breaker (yes they can go bad, its not common but can happen). Maybe the access door is not secured quite right? Was any work done right before this started happening?
Our White-Rodgers Thermostat had a blank screen and the AC was off. Researched what could cause this and came across this podcast. When I read about an on/off switch that had been turned off, I started thinking about how I was flicking mystery switches in our garage off today and on wondering what they went to. Now we know. Switched it back on and the AC unit starting working. THANK YOU!!!!
Thank you so much for this post. After changing the batteries, the display still did not come on. I didn’t know to hit the up& down buttons while turning off/on!
Thank you, I followed your above device for resetting my thermostat and it worked!!!
Thank you very much you just saved me thousands.
OMG! It’s 10 pm and I got home about an hour ago to find my a/c off and my thermostat dead! I searched and found this site and did exactly what you said and it’s fixed!!! Thank you so much!!! I feel like I have extra money in my pocket and will be able to sleep in a cool house!
Hi I have a question. I woke up this morning and it was going to be a cool day so I turned off my ac and opened up windows…. when I got home and had dinner and was getting ready to go lay down I went to turn on the ac for the night and my thermostat (Honeywell th-7000 series) just lights up but displays nothing. It is only a touch screen no buttons and of course I can’t find anything at all online. Please help
Check the things in this article. If that doesnt help then call Honeywell at 1-800-468-1502 or call your HVAC tech.
My a/c was working fine. Then the thermostat went blank and the unit won’t come on. My husband replaced the batteries and still no screen or a/c. Only the fan will turn on. What shoukld I do?
Try the steps in the article. If those dont work call a pro.
Trying to troubleshoot a Honeywell thermostat. Instructions say to turnoff. Does that mean the circuit breaker to the furnace or to switch the thermostat to off?
so, what if you live in the west,where we dont have furnaces or basements? we have central h/ac. where is the main box?
In a closet somewhere, or attic maybe or outside maybe.
My thermostat had gone blank also. I went through the steps and found that my front cover had come loose in the attic and simply needed to be put back on securely. I had changed the filter a few days ago and did not secure it correctly. Thank you for this information. Very helpful.
THANK YOU Brian … you saved me a service call.
Hi, thanks for the info above. I did the trouble shooting and the display still goes blank. It is blank and the ac shuts off. Replaced batteries and it comes back on for about 15 min then shuts off again. I repeat the process about every 15 min and the same thing keeps on happening. I try to adjust the temp and it shuts off again.. Could it be a faulty thermostat?