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No display on the thermostat and no AC

by The Handyguys

in Blog Posts, Handyguy Brian

Handyguy Brian had the following conversation, via instant messaging, with his lovely wife (or so he thought) about how to troubleshoot a no display issue with a thermostat and no Air Conditioning (AC). No audio here.

Some steps for troubleshooting your AC, thermostat or heat.

thermostat went blankBelow 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??

Sarah: yes

me: hmmmmm

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: yes

Sarah: 1F86-241

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

Sarah: kk

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

me: whew

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 one the phone!

me: ahahhahah

she did all that?


Sarah: ye


me: hahha

toooooooooo funny

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.

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{ 75 comments… read them below or add one }

Sarah Hill June 21, 2011 at 3:15 pm

Funny! We have those conversations with people everyday. Good thing we know so many great servicemen to help them out. Thanks for sharing!


Jay July 14, 2012 at 10:19 pm

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.


The Handyguys July 15, 2012 at 5:06 pm

Good catch – Just make sure the drain is not clogged and the pump is working so you don’t have the issue again.


Michelle Gates November 24, 2012 at 10:52 am

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.


Maria May 26, 2013 at 9:29 am

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


The Handyguys May 28, 2013 at 9:33 am

This sounds like more than a thermostat issue. I would suggest calling a AC repairman.


murali June 28, 2013 at 4:56 pm

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?


The Handyguys June 29, 2013 at 10:00 am

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.


maria September 23, 2013 at 2:21 pm

my thermostat is not displaying the temperature just HL what does that mean?


The Handyguys September 24, 2013 at 9:01 am

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.


ralph a. applegate October 29, 2013 at 4:42 pm

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?


The Handyguys October 31, 2013 at 2:08 pm

It indeed could be a breaker or fuse. Check those before calling for service.


scott November 24, 2013 at 2:27 pm

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



izy January 25, 2014 at 5:46 pm

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.


Inita February 5, 2014 at 11:24 pm

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


D.Sant February 25, 2014 at 1:01 am

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.


The Handyguys February 25, 2014 at 8:27 am

Good job!


Chris March 4, 2014 at 9:34 pm

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 Handyguys March 5, 2014 at 12:02 pm

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.


Mike April 10, 2014 at 3:25 pm

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!


Candice June 6, 2014 at 8:48 pm

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!


The Handyguys June 9, 2014 at 10:03 am

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.


Vikki Floyd June 13, 2014 at 12:49 pm

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?


The Handyguys June 16, 2014 at 3:43 pm

It doesn’t sound like the batteries. I assume its not really 48degrees next to the thermostat. It may be due for a replacement.


Cheryl June 26, 2014 at 2:25 am

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


The Handyguys June 26, 2014 at 11:06 am

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.


Jimmy June 26, 2014 at 10:47 am

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.


The Handyguys June 26, 2014 at 11:08 am

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.


Jimmy June 26, 2014 at 11:59 am

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????


Jimmy June 30, 2014 at 1:10 pm

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.


The Handyguys July 1, 2014 at 3:57 pm

Good find!


Anna Huthmaker July 7, 2014 at 4:30 pm

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!! : :


gretchen August 8, 2014 at 6:13 am

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


The Handyguys August 11, 2014 at 8:15 am

They lost power somewhere. Maybe a fuse in the outside disconnect (if you have that). Maybe a tripped breaker.


Liz Morrin August 10, 2014 at 9:56 am

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.


The Handyguys August 11, 2014 at 8:14 am

My first guess would be the wires to the thermostat are installed incorrectly.


Kevin Burnham August 10, 2014 at 10:17 pm

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!!!


Mark in Louisville August 16, 2014 at 10:19 pm

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!!!


Ras August 16, 2014 at 4:33 pm

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


Dan August 18, 2014 at 11:37 am

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.


The Handyguys August 18, 2014 at 2:12 pm

There a a contact switch on the door to the bottom of the AC. Perhaps the door is not seated all the way.


Angie August 30, 2014 at 11:11 am

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


The Handyguys September 2, 2014 at 10:12 am

Bad batch of batteries perhaps.


angie September 11, 2014 at 7:04 pm

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?


The Handyguys September 16, 2014 at 10:34 am

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.


Doug September 15, 2014 at 10:36 pm

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..


clei September 26, 2014 at 10:10 am

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!


The Handyguys October 2, 2014 at 9:41 am

Make sure you re-installed the wired correctly. You could also have a bad thermostat. Beyond that, not sure.


Jackie November 17, 2014 at 1:40 pm

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?


The Handyguys November 18, 2014 at 4:34 pm

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.


christina December 1, 2014 at 1:02 am

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?


The Handyguys December 2, 2014 at 8:26 am

Make sure the access door to the furnace is closed and installed correctly. There is a safety shutoff switch in the door.


Richard January 2, 2015 at 11:59 am

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.


The Handyguys January 2, 2015 at 7:03 pm

Has it always done this or is this a new issue?


Richard January 3, 2015 at 2:38 pm

It just happened two days ago, I never have this issue before. what cause it ?


The Handyguys January 6, 2015 at 10:01 am

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.


Richard January 2, 2015 at 11:47 pm

This is the 1st time it happened like that and i don’t know what to do. Any suggestion?


The Handyguys January 6, 2015 at 10:02 am

Try the suggestions in the post above ^^^


Sam January 6, 2015 at 9:42 pm

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.


Suzanna January 19, 2015 at 9:29 pm

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!


don January 22, 2015 at 6:50 pm

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!!!


The Handyguys February 2, 2015 at 3:03 pm

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.


Shelley January 29, 2015 at 9:31 am

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.


Mimi January 30, 2015 at 11:01 am

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?


The Handyguys February 2, 2015 at 2:59 pm

Make sure the door to the air handler is properly closed plus the steps in the post above. If nothing, then call a pro


Mimi February 17, 2015 at 1:53 pm

It still is not coming on. Thank you for your assistance.


Sarah February 1, 2015 at 11:23 am

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!


Steve February 15, 2015 at 12:20 pm

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


The Handyguys February 16, 2015 at 11:43 am
Bernard February 28, 2015 at 4:08 pm

My A/C won’t work… No display at all… My thermostat is robertshaw 9520


The Handyguys March 2, 2015 at 2:55 pm

Try the above checks ^^^


Heather February 28, 2015 at 7:34 pm

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.


The Handyguys March 2, 2015 at 2:56 pm

Correct, if the battery dies it will not follow the programing.


vincile March 6, 2015 at 10:56 pm

What is that switch knob for on the inside of the thermostat?


The Handyguys March 9, 2015 at 8:17 am

No idea, all models are different.


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