Air-Conditioning Troubleshooting Checklist

In this episode of The Handyguys Podcast we discuss air-conditioning.

Lennox AC unitAir-conditioning is not something the typical handyguy or girl is familiar with. We turn it on and expect it to work as designed. What can we do if it doesn’t cool? Are there specific things to look for before calling in a pro to troubleshoot?

With high humidity and soaring temperatures this summer, the last thing you want to deal with is a broken air conditioner. But when an old air conditioning system fails, you will be faced with the tough and often expensive decision of whether to repair the existing system or purchase a new one.

Repairs on an existing unit may be the least expensive immediate option, but could cost you more in the long run since older systems tend to break down over and over and consume more energy and drive up cooling bills more than newer systems. However, there are times when simple repairs can prolong the life of an air conditioner, making immediate replacement a less sensible option.

Since the Handyguys are not experts in this area and we want to help you make an educated decision, consider the following tips from Bill Cunningham, a home cooling and energy efficiency expert with Lennox. Bill shares a great deal of wisdom and experience with residential central air-conditioning systems, regardless of who manufactures your system. He suggests homeowners ask the following three questions before making the decision whether to repair or replace:

  1. ACIs the air conditioner on its last leg? Excessive energy consumption and frequent repairs are the trademarks of a worn-out system. If the air conditioner is more than 10 years old, replacing the aging system with a new ENERGY STAR-qualified system can save time, money, and headaches – and keep you cooler and more comfortable in the long run. If the system is less than 10 years old, routine maintenance is almost always the way to go. In fact, an annual check-up can significantly increase the air conditioner’s performance and extend the life of the unit. Listen to the podcast for more information.
  2. Are your energy bills going up, up and up? While the cost of electricity is on the rise, an older, less efficient air conditioner may also be the culprit when it comes to high energy bills. By replacing an 8 SEER (seasonal energy efficiency rating) cooling system, which is much less efficient than the current SEER level allowed by law, with a 15 SEER system, homeowners can save approximately 47 percent on energy bills and up to $3,095 over a five-year period. Energy calculators, such as the one available on the Lennox site can help consumers compare the savings of different high-efficiency systems and determine whether to repair or replace an older unit. Listen to the podcast for more information.Thermometer
  3. Did your home feel like a steam room even before the air conditioner stopped working? A poorly operating air conditioner or one that is not properly sized for the home can contribute to excessive humidity. Leaky ductwork can also cause humidity problems. When making the decision to repair or replace, talk with a reputable home cooling contractor about the humidity problem to determine if you need to replace the existing system with one that is the right size for the home or if the issue can be resolved with repairs or duct sealing. Listen to the podcast for more information.

We also discuss with Bill a few things you can check yourself before calling a service tech.

  1. ThermostatDoes your thermostat use batteries? Many of the fancier thermostats use batteries. If your batteries are dead your system will not work.
  2. Did a breaker trip? Its an easy check and will save you the cost of a service call. Look for a tripped breaker if you have no fan or no cooling. You likely have separate breakers for each.
  3. Did someone turn it off? Systems usually have switches for killing the power before service. There will be one near your outside unit as well as near your inside unit. There may also be a switch at the top of your basement stairs or somewhere nearby.

Listen to the podcast for more information.

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Thanks to for sponsoring this post – For the outside parties and cold evenings patio heater hire will keep your guests warm.

57 thoughts on “Air-Conditioning Troubleshooting Checklist

  1. I believe that the biggest factor in weather t repair or replace would lie in the repair that needed to be made. In many cases your ac unit may be operating at higher utility consumption than previous years due to lack of maintenance. The pay back may take more than 10 years and what then at that point? purchase another unit? It is extremely important to look at the over all performance of the compressor ( the heart of the system) and make an informed decision from there. The valve should be tested as well as the motor windings. As the owner of an air conditioning repair company in Chicago I have seen too many people replace units that would have lasted another 10 yeaars. Just my 2 cents

    1. Mitchell – Good point! Yes, I agree. If a repair would only cost a couple hundred dollars and give you many many years of service then yes, do the repair. On the other hand – if you are spending hundreds a couple times a season every year then maybe its time to consider a replacement or at least a service contract. I think the bottom line is that routine maintenance will help minimize the chance of some repairs and prolong the life of your investment.

      1. I understand what everyone says about routine maintenance, but I feel you can end up losing in the long run. The service contracts are complete ripoffs, and all you get for handing over hundreds a year is a small discount on parts. On top of that, it is very hard to find an honest company these days, and who knows what they will do to your unit when doing routing maintenance. You can read horror stories all about this, but you rarely read how a service contract saved someone. Probably because it saved them $75 on a repair while paying $4,000 in service contract fees over the life of their unit.

  2. Service contract! Absolutely! Thank You. It is at times frustrating to get people to understand and implement the HUGE benefits of a routine scheduled maintenance agreement. I must say it is refreshing to correspond with someone who can see the value in maintaining your ac and heating equipment on a regular basis. Don’t get me wrong there are lot’s of people that are diligent in maintaining their equipment and these are the people that have the least problems with their equipment. Once again, it is a pleasure to see that others feel as strongly as I do in service agreements. Mitchell Moore

  3. I’m servicing a Rheem 3 ton condenser and Air handler. Upon recieving the service call the owner told me the unit goes on and initialy cools then goes warm. My first thought was low freon(leak) or poor air flow accross cevaporator coil surface Freeze up).I just had an initial start up on a 82 degree day and the unit is blowing warm air. I first checked the filter and electronic air cleaner which was very clogged (i cleaned). Evaporator coil is in decent shape as far as being dirty,and the condenser needs cleaning. After initial check points and before putting the gages on i ran the unit with the air handler side only.(seems fine) Then i put the gages on and set the thermostat to call for cooling. The gages read 30 psig and i had no reading on the high side. One would think a leak. I did a Freon charge and brought the system up to 60 psig. Still no reading on the high side. At the evaporator there using a .065 orifice. System seems to be running fine. Why would i not have a reading on the high side. After leaving the job i thought maybe someone did service on the system and didn’t back off the valve fully on the high side. If that’s not the reason would it be recommended to pump down system and install a new orifice. And if that doesn’t solve the problem would you think the Compressors valve assembly is leaking and the compressor isn’t pumping,Which would call for a change-out?

    Help would be appreciated


  4. I have another home-owner / DIY troubleshooting point:

    When I installed my central vac system, I unplugged the condensation water pump to our AC so I could run the line. I forgot to plug it back in (figures…) and it of course filled up with water. Since I have a new high-efficency unit, it of course comes with an interlock that won’t allow it to function if the little pump pan is full.

    I called the service tech, and he didn’t catch it either, so he started swapping parts. Since he didn’t follow the troubleshooting checklist, he gave me the service call for free – and I got a few newer parts in my system.

    Lesson: check the little tank.

  5. The outside unit fan blade locks up and starts making a noise that sounds like it’s trying to run ! With water hose u can manualy get the fan going and it will start up . Cool house down then it will do it again. Does it need a hard start?

  6. My inside handler unit is constantly leaking water inside the closet. I’ve cleaned the lines that lead to the outside and also cleaned the pan and removed all the gunk that was accumulated. I even sprayed an a/c cleaner on the coils, which did not really look that dirty. After all that work, the a/c began to leak again thirty minutes later. The house is cool and the system seems to be working fine however the closet and filter are soaked. I’m frustrated and don’t want to call a company just to discover that it was something simple that I was not aware of. Please help.
    Thanks, Nelson

    1. Nelson – Thanks for your question. I think you are on the right track. You didn’t say if the pan is filling up and overflowing on not. I suspect not. The pan may have a leak in it or drain the line has a leak. The drain line is relatively easy to replace if you have access. The pan could be a much bigger job. See if you can determine exactly where you leak is and where the water is coming from. Once you do that you will be well on your way to determining a fix.

  7. well i need help with my central air we had it turned on previously came home today and it shut off wont turn on at all.. I replaced the fuse non of the breakers were tripped! What should I do now??

  8. i live in an apartment and my lennox air conditioner seen like it not doing the job i thought it would!!! the unit is sitting on some rocks and isn’t balanced and the black rubber around the pipe is worn baddly. ((( I can see the pipe in half the pipe from the unit to the wall))) do this thing matter??? thanks mark 4e

    1. The black rubber is insulation. It matters as far as efficiency goes but if your AC isn’t cooling the insulation isn’t your problem. You live in an apartment, call your maintenance person and have it checked out.

  9. Unit not cooling. Fan comes on. Checked outside fuses-both good.
    checked breaker-it had not tripped. Tripped and reset. Still no air. Turned thermostat way down- ac unit doesn’t start. What next?

    1. I’m assuming the outside compressor is running when the thermostat is calling for cooling. If it is, its likely a coolant leak. Fixing a coolant leak is not a DIY project, its time to call in a pro.
      Some pros may just top off the coolant and call it a day. That may give you cooling for a day, maybe for a week or maybe for a season. It all depends on how bad the leak is. Others will do a pressure test to find the leak and attempt a fix before adding coolant. Other pros will just say you need a new compressor, lines and other parts. I would get 2 or 3 estimates. If you AC unit is more than 15 years old then the person recommending replacement may be correct. The guy who just wants to add coolant and see what happens will be the cheapest but he really isn’t fixing the main cause (a leak). Good luck and post back here what the pros fix was.

  10. my outside unit will not turn on. I have replaced bus fuses and checked for tripped breakers , plus check tremstat. I turn it on to cool and the fan on the inside unit turns on but the outside unit will not in gage. Is there a reset buttom or switch for the outside unit. pls help me.


    1. No, no reset button. There is sometimes a disconnect switch and/or a fuse or breaker outside. If all those are fine then it may be time to call in a pro. Good luck, sorry I couldn’t help more.

  11. I have an outside Bryant unit, It has been tripping the breakers lately.
    It will come on run for 45 min- to an hour , sometimes 15 min- 30 min then the fan shuts off then theres this hiss, pop, and a few other sounds by the time get back to the thermostat to turn it off it trips the breaker. I did some trouble shooting and thought it might be the fan motore, so I replaced the fan motor today. However i turned on the unit and wammy 15 min, and it shut off again but did not trip breaker. I’m contemplating to replace the capacitor tomorrow, I cannot aford a new unit for $2500, but i can spend a $112 on a new fan motor and the capacitor is $83 thats still better tthan $2500. I’ll just have to try and get buy till the economy picks back up. If anyone can give me some pointers as to what’s going on please help. The only last thing I can think of id the compressor, and well I have a new unit once i have to put it in. Help! Hot in lower Alabama today was 100* at the beach – heat index 116*, Were melting!

    1. The Handyguys are not Professional HVAC guys but it sounds like you are on the right path. Fan motor, capacitor, or the compressor. A good Pro HVAC person might have the tools to test these components. In your case its a best guess. Does the capacitor(s) look damaged or leaking anything? I might start there. I might also see what parts are warm to the touch after tripping the breaker. The compressor will be the most expensive part.

  12. If you have old doors and windows in your house and it is not air tight in your house, it will cause your air conditioner to work overtime and that will shorten the life of it. Always monitor your usage regularly.

  13. I used the air conditioner for the first time this year. The outside unit sounds fine. The furnace fan was blowing cool air through the vents for approx 4-5 minutes, then furnace kicks on blowing hot air. I turned the unit off,waited a few minutes and reset thermostat to auto-cool. Same results. Last fall the furnace would not work so I replaced the old round thermostat with another of the same type. The furnace worked fine after that. What would cause the air conditioner to suddenly stop and the furnace to light? Thanks Dan

  14. Hello, I have a lennox air conditioner, it works fine and blow cold air! The problem is when it shuts off it makes a horrible howling/squealing sound and the line vibrates something awful any ideas????

    1. No specific ideas. The issue is likely in the motor, the compressor or the connection between them. I would visually inspect the unit for anything obviously damaged or physically interfering with the operations. if nothing is obvious I would call an HVAC tech in.

  15. Hi. I have a 3 year old Lennox System. The system cools and heats properly. It has a programmable thermostat and the batteries are new. The problem is, the system will run, only when I go down stairs and flip the breaker for the “A/C” unit off for 5 seconds then on. It works perfectly after that, cools down the house just fine. It has done this twice so far in one day. Do I need to replace the thermostat, that is only about 3 years old too. Usually when I adjust the temperature on the thermostat to a lower temperature it will automatically turn the system on. The past day, it won’t turn the system on, I have to go flip the breaker (which is not tripped). What gets me is that it is almost as if I am “resetting the system” by flipping the breaker.

    1. Sometimes breakers don’t look tripped but they are. Are you sure the breaker is nto tripped? That is what it sounds like. Either way, if the breaker is tripping, or if you are having to reset the system, I dont know of any DIY fixes. I dont think replacing the thermostat will do anything. I would suggest a lenox tech come out to repair. May have some parts still under warranty.

  16. I have a lennox a/c unit that the compressor was just replaced in. It functions correctly by blowing cold air ,but when it starts up it make a howling/growling sound for a few second or two…every time it starts up

  17. I’ve got no air whatsoever blowing into the house. The outside unit comes on and the inside air handler is on, but nothing is coming out of the vents. Also, I’ve got water dripping into the empty space under the air handler and the unit itself has condensation all over it. Don’t think I have an overflow problem, but not sure. Went to bed last night and it was working fine. Woke up this morning and the air handler was on, but the outside unit was not. I checked and flipped all the breakers and the outside unit came back on, but still no air blowing. What’s going on?

    1. No air blowing means your air handler has stopped. This could be a bad fan or an electrical problem. Dripping water below the air handler means you have a failed condensate pump or drain or a clogged drain. I cant pinpoint the issues based on the description. I would suggest calling in a pro, you may have multiple issues.

  18. BUmping to this discussion, warranty is always a must. Any one who purchase stuff weather its cheap or expensive, there should be assurance of it.

  19. My unit is blowing air out of the vents but it is not cold. The outside unit comes on, the compressor comes on, the air handler in the house comes on, digital thermostat with new batteries, and a brand new filter. The water return line is not clogged. Anyone can help of have any ideas what else to look for?? I live in S. Florida and it is HOT!!! Please help

    ~Mother of 4 on a thight budget

    1. A likely cause is a freon leak. This is not a DIY fix. The cheap ‘fix’ would be to add freon. That could give you cold air for an hour or a day or a year. A good tech will pressure test, find and fix the leak then refill the system. Good luck.

  20. HVAC not working or showing any numbers on the Thermostat I have check for power at Thermostat and did find 3 amp fuse blown. Replaced 3 amp fuse twice but keeps blowing fuse. What is my next step?

  21. We put new duct work in and closed it all up. It stopped working cleaned it all out with vacumm. It started working then after a couple hours it stopped working again. The duct work was not conducted when we moved it. Any ideas

  22. our Lennox air conditioner is 3 years old. The vents in house blows cold air but I hear the fan turning on and off so air comes out of vents and stays on like a minute and goes off. It just continues to do that. What is wrong there is no ice and we put a new filter in can’t see anything wrong.

  23. Unit working fine but had yearly check done today to be proactive. Now fan or inside unit will not come on at all. Help!!!!

    1. Well – I would call back the guy who did the check. He SHOULD make it work again no charge. He likely didn’t install the access door correctly. There is a safety cutoff switch on the door. Or, he shut something off to service/check and didn’t turn it back on. Just check the access door on the inside unit and make sure it looks like its on correctly. Let me know what you find.

  24. Our unit starts and then stops after about 10 minuts
    The thermostat works fine and the breaker is ON
    What could be the problem ???

    1. Many things could be wrong. Possibly a sensor of some type. You could check the main access door safety switch. Also check the drip pan to make sure its not full of water or the condensate pump (if you have one) is functioning. Maybe even check the filter.

  25. None of the suggestions worked! Called service co. Last night and they called here at 7:15am. Should be here any time now! Disappointed they did not come right out. We have used them for years and bought the unit from them a few years ago!

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