Posted on 29 Comments

Air conditioner troubleshooting flow chart

happy ac

We have an air conditioner troubleshooting flow chart if you would like a step by step approach to air conditioner troubleshooting.  Please click here if you would like to see a PDF Air Conditioner Troubleshooting Flow Chart. We hope this chart will help you quickly troubleshoot and repair your air conditioner or heat pump. If you have any questions please email us or comment below. Our email address is: We would Love to Help You out and have your business!



29 thoughts on “Air conditioner troubleshooting flow chart

  1. so I have a water source heat pump Carrier Brand. M#50PCH060WCC5ACA1
    S# 1518v78144

    Getting blink code three flashes. Which states Condensate freeze protection. I checked the complete system for any electrical issues. Couldn’t find anything wrong. Unit will not heat/cool either mode. I checked the freeze1 and freeze 2 FS1 and FS2 on the board. jumpered them out like the notes say to do. Nothing happened in heatin or cooling, just the fan runs. I checked the oms out on the two sensors from FS1 and FS2 and got like like 11,000 to 12,000 ohms. I believe it might be the main board that is bad? I dont believe its the sensors. Any ideas? i ordered a new board and will try that and hope it works. Any way to test the main board to make sure that is the issue?

    1. Hi Dave! I am very sorry, but I do not know anything about water source heat pumps. I have never installed any and have never worked on any. I am sorry that you wasted your time emailing me. Maybe someone else has an answer. You might want to get into the HVAC talk forum and see if any of those techs have an answer. Here is a link to the site: I would like to suggest that you Google “Water source heat pump troubleshooting” if you have not done this already. I sure hope you can find a solution to your problem soon. Steve

  2. steve last winter my furnace would not work only ac had bought pilot light and furnace worked now its summer I turn on ac and the furnance comes on I have new thermostate set to cool and auto replace the wire last year to the breaker is good

    1. Hi Rick!
      You might need an adjustment to the settings of the new thermostat that you installed. I would suggest looking in the thermostat installation book and see if there are different settings for different furnace/AC systems. You might have the thermostat wired wrong. The W connection on the thermostat is usually what powers the heat or gas valve on the furnace. Make sure that the W connection is not being energized in the cooling mode. You might have a short in one of the thermostat wires that is carrying over to the W wire when you have the thermostat set to cool. I hope the following post that we have will help you out: Steve

      1. thanks I found the problem sort of on the 24 volt wire on ac was not connected put new end on ran fine for 2 days but would not shut off auto then did not work at all I got 120 to everything at ac but no 24 volt at all I went down to furnace and I only got 24 volt to red wire nothing to white green yellow I know white is heat yellow air green fan its only four wire I checker the transformer it has 24 yellow to board and 24 to blue to board any thoughts why no voltage to yellow green white but do have to red at board on furn. nothing to ac white or red thanks for your help

      2. Hi Rick! With the thermostat calling for cooling to be on you should read at your furnace’s control board 24 to 28 volts AC between R and C, Y and C, and G and C. If you are not reading 24 volts between those terminals then you either have a thermostat problem, thermostat wire problem or a low voltage transformer problem. You could have a loose wire connection in one of the wires. If your thermostat uses batteries the batteries could be low on charge. I hope that you can easily find and fix the problem. Steve

  3. I working on a sir frost hp and the board is flashing all three lights as in green yellow red and its driving me crazy please help

    1. Hi Ray! I am not familiar at all with Sir Frost heat pumps. I would like to suggest that if you can try to find what the flash code means on the control panel door. Hopefully, this might help you out. I am sorry that I can not give you any advice on what could be the problem. Steve

  4. Can the compressor blow fuses if it is going out? Thanks in advance

    1. Yes, the compressor will blow circuit breakers if it is grounding out, but rarely low voltage fuses. If a low voltage fuse like a 5 amp or 3 amp fuse is blowing out then you probably have a thermostat wire problem or another low voltage control that is grounding out causing the problem. If the high voltage breakers are blowing them more than likely you have a locked compressor or a compressor that is grounding out. We have Youtube videos on how to ohm out a compressor to see if it is bad or not. If the emergency heat will not work then you probably have a low voltage problem and might have a short in the low voltage thermostat wires or a heat pump control like a contactor, sequencer or reversing valve. If you are not familiar with working with electricity I would strongly recommend that you get an HVAC company to troubleshoot and fix your problem. Heat pumps and electric heat can be hard to troubleshoot because they are pretty complex. If you have any questions please let me know. I hope you can find and fix the problem soon!

  5. I have a heat pump system that is blowing cold air. The outside fan is running. I had a guy out to look at it, he only looked in the inside unit and said that the coils were dirty and needed to be removed and cleaned and that I had a bad relay switch. He said the repairs would take too long and he would have to come back on Monday. My concern is that he hasn’t checked the outside and if these things are bad would that be causing my problem or is there likely something wrong with the outside unit as well. My fear is that he’ll fix those problems and then find a bigger problem. I really can’t afford to fix those two problems just to find out that I need a new unit.

    1. Hi Jm! It sounds like the service company was in way too big of a hurry to take the time to troubleshoot your heat pump correctly. Yes, the tech should have hooked up gauges and analyzed the refrigerant temperatures and pressures in your system to make sure everything is running right. Yes, if the tech is going to take the coils out and clean them then this would take a lot of time. He should have installed guages to make sure that your heat pump compressor and metering devices were working properly because cleaning the coils could be a waste of time if the compressor and metering devices are not working right. I would question the tech when he comes back on Monday to insure that by cleaning the coil and replacing the relay switch is going to fix your heat pump. If he does not give you a definite answer then I would ask him to leave and I would suggest that you get another company to troubleshoot your heat pump. You should be able to run on AUX heat if possible until your heat pump is fixed unless the relay that needs replacing is the blower relay. Sorry that the tech was in such a rush and did not have time to fix your heat pump. I hope that you get better results and repairs on Monday. God bless you and your family today and always. Steve

  6. I have a 1994 Nissan Quest. My ac blows hot air when I turn it on.

    1. We do not normally respond to auto air conditioning problems, but this sounds like your air conditioner could be low on charge or the compressor might not be working because of the low-pressure switch cut-off or other problem. Sorry that I do not know much about automobile air conditioners.

  7. Steve,
    I have a Senville SENA-18HFO. It stopped heating in February. I use it in the basement and looked at it this week. I am a retired HVAC tech and live in Pa.
    I turned it on and went directly from 240 psig to a low vacuum. I removed the charge of 410a and recharged with exact amount 4lbs, 3ozs. I did evacuate system for several hours and held vacuum for another hour. Leak free. (before recharging) System acted the same after, turned back on.
    Than tested reversing valve. Runs on 220 volts. When power applied can hear and feel valve moving.
    Pumped down system into outdoor unit. Disconnected high side line and put 410a into low side gauge port. No restriction found thru indoor unit. Added a service port to high side and disconnected low side line. Put 410a into high side and flowed thru indoor unit, and low side line without restriction.
    Turned the system back on to observe high side reading. To my surprise it goes into a very low vacuum identical to low side. I have contacted Senville, but they have not replied in four days. Thanks in advance.

    1. Hi Stanley! I am sorry, I have no idea what your problem could be, but it sounds like there is a restriction somewhere. You have tested for restrictions and the system does not seem to have any. I have never heard of this. I would suggest that you try to contact Senville again. Sorry that I can not be any help.

      1. Steve,
        Yes, when I have a problem I cannot solve, its generally a unusual problem. The unit ran trouble free for five years. These units are difficult to find parts for, and to speak with a tech at the company. Thank you very much, and I enjoy reading, information posted at your site.


    2. Check Cap tube at Drier ,after some time running cap tube is resting against screen and you will get build up closing off cap tube

      1. Great idea! Thanks so much for sharing this!

  8. i have a Goodman HVAC at a house that we just bought in Florida. Upon starting the AC it ran for about 20 minutes and shut off.
    Than everytime after it ran the first time, everytime it came on the run time was lesser than the time before. after a couple of hours it would run for about 5 minutes than shut off. Now it comes on and shuts right back off for only a couple of seconds and shuts off. After a 5 minute pause it comes bak on for a couple of seconds and shuts off again.
    If you have the part for me to fix this problem, how much will the part cost with the shipping and handling charge?
    Thank you,
    Bettie Korbilka

    1. Hi Bettie! Sorry to hear that you are having trouble with your AC in the hot Florida weather. I really have not idea what the problem could be without being there to test some components. I would suggest that you look and see if the contactor is staying energized with 24 volts on the contactor coil. You will need a volt meter and some knowledge about electricity before troubleshooting. If the contactor is not being energized then you could have a thermostat problem, thermostat wiring problem, low or high pressure safety switch problem or a time delay relay or defrost control board problem. If your thermostat has batteries make sure the batteries are in good shape. We have lots of air conditioning and heat pump troubleshooting questions with answers and Youtube videos on the following page: We also have an air conditioning and heat pump troubleshooting simplified page that I hope will help you find and fix the problem: We also have lots of troubleshooting advice on the following page: If you have any specific questions please let me know. I hope you have a great day! Steve

      1. My outside AC unit will not turn on.
        There is no hum, no sound at all.
        It had been working great, then one morning only the furnace was blowing.
        I have checked my breaker twice.
        I have 25 volts from the therm and the contactor energizes.
        I know my way around meters.
        I have 110v everywhere when I go from ground to everywhere, (contactor both L and both T)
        I have 110v at the compressor terminals
        What I don’t have is 220 across both L coming into the contactor.
        Could 1 of the copper fuses in the shutoff box be blown ??
        (I watched your video where you also didn’t have 220 across the L, but you continued to talk about the working contactor, and not how to test the shutoff box for proper current going to the contactor. Please help, there is a dangerous heat wave coming to Chicago and the kids are already complaining.

      2. Hi Jim! Sorry to hear that your AC is out. As you know you should be getting 210 to 245 volts between L1 and L2 from you home’s disconnect box and with the contactor energized with 24 volts going to the contactor coil you should have 210 to 245 volts AC on T1 and T2. Yes, you could have one of the fuses blown. Here are some Youtube videos that I found on how to check various air conditioning unit disconnects: I hope this helps you find and fix the problem. Steve

  9. Why would my heat pump call for heat even though I have set thermostat to cool? I went outside and unplugged the heater coil to get my a/c to blow cold again but this isn’t a fix. I have a York heat pump, Model B3HP024A06A

    1. Hi Matt! A heat pump could blow heat in the summer when set to cooling if the reversing valve is stuck or has not received 24 volts to the reversing valve solenoid to make the reversing valve shift. Most heat pumps other than Rheem, Ruud run the cooling cycle with the reversing valve solenoid energized with 24 volts. If the solenoid is not receiving 24 volts from the thermostat through the “O” (usually orange wire) or if the solenoid coil is bad then the heat pump will stay in heating mode. A faulty defrost control board can also cause this problem. With the thermostat set to cool, AC ON, I would suggest that you pull the high voltage disconnect so the outdoor unit does not run then check to see if you are getting 24 volts to the reversing valve solenoid coil. If you are not then you will need to find if you have a thermostat problem, loose thermostat wire or a defrost control board problem. I hope you can easily find and fix the problem. Steve

  10. One of the best information sites I’ve been on.

    1. Thanks so much for your kind words! Hope we can help people troubleshoot and fix their HVAC systems. Steve

  11. Wow you’re web is so awesome totally ran me through everything I needed would recommend you guys above all of the other I have seen thank you so much for your help I am going to build an account and order my parts my name is Greg Hundley. THANK YOU

    1. Hi Mr. Hundley!
      Thank you so very much for your kind words and business! I just received your order and we will get it shipped out soon. We really appreciate your business! Hope you have a great day! Steve

Leave a Reply

Your email address will not be published.