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Problem: AC Unit Not Turning On-How to Fix it.

troubleshooting air conditioners and heat pumps

Problem: My air conditioner will not turn on. What could be the problem with my AC not turning on?

Answer: I found this excellent YouTube video from Word of Advice TV that explains many problems that can cause your Air Conditioner to not work or come on. This is one of the best videos I have ever seen on troubleshooting an air conditioner. I hope this helps you find and fix your air conditioner or heat pump system. If you have any questions please respond in the comments below or email me Steve Arnold at: Support@arnoldservice.com. Thanks so much for giving us the opportunity to serve you! Hope you have a blessed day! Steve

10 thoughts on “Problem: AC Unit Not Turning On-How to Fix it.

  1. My original problem was the AC fan spins but the compressor was on for a second then off for about 1-2 minutes then repeat. I had LPS light on AC control board showing it was fine. I then replaced the capacitor and removed/clean the contactor switch (full of bugs/webs). Afterwards, I tested the unit by pushing the plunger on the contactor but forgot to turn on the TSTAT cool/fan on and the AC compressor/fan started. I then turned the TSAT to cool and now the AC fan/compressor stay off with the LPS light is off and testing the LPS switch with ohmmeter is Open. The HPS light is on at AC control board as expected. I verified 26v is coming into the AC unit and to the board and the contactor is not getting 26v. Could pushing the contactor plunger and not putting on the TSTAT fan cause the LPS to become Open or cause freezing in the lines/coils that last for days or break the AC? If I press the contactor plunger the AC fan and compressor both start up but the LPS light on the control panel is still off. I also verified the compressor pins do not ground , and the sum of CR+CS=SR with CR the smallest value. HELP what should I try next? The unit is a carrier Model#24aca436a300 Product#24aca436a0030010. I’ve learned tremendously from your videos to get this far but now I’m stuck!

    1. Hi Bill! I would suggest that you make sure that any low voltage fuses are not blown. There should be one on the control board. Maybe you accidentally shorted one of the wires out. I have no idea. Many of the new air conditioning units are quite complex in how they are designed to operate. I have not done any service work on air conditioners since 2005. New AC units are a lot more complex on how they operate now. If your unit has been freezing up then this most of the time is a sign that your unit is low on refrigerant charge or you have a blower motor that is slow dirty or going out. I would suggest that you get a tech to install guages and see what or if you have a problem with the pressure readings. Pushing in the plunger on the contactor should not have damaged anything unless you accidentally grounded a wire out. I am sorry, but I have no idea what your problem could be without doing a series of tests with a volt meter. If the power is going in and not coming out then more than likely it is a problem with the part that is not allowing the power to come out. Sorry that I could not help you out. Steve

  2. How to change a heat pump condenser to straight cool for a straight cool unit on the inside

    1. Hi Joe! I do not know for sure if this is the answer you are looking for, but if you want a heat pump outdoor unit to be an air conditioner all the time you would have on most heat pumps the “O” reversing valve energized all the time. On most heat pumps the reversing valve solenoid is energized in the cooling mode to shift the reversing valve into cooling. Rheen and Ruud are the only units that I know of that have the reversing valve energized in the heating mode. So you would need to find a way for your thermostat to energize the contactor, reversing valve and indoor fan blower when the thermostat calls for cooling. So R(power wire) to Y would energize the contactor. R to O would energize the reversing valve and R to Green (fan blower) would energize the indoor fan blower. I hope this is what you want for an answer. Steve

  3. I’ve got the light flashing 7 time on the fan control board.

    1. Hi Ed! I would like to suggest that you try to find out what the flash code means by looking at your unit’s blower door or control panel. Different brand furnaces and air conditioners have different flash codes. Sorry that I can not give you any advice. We have lots of air conditioning and heat pump troubleshooting questions with answers and Youtube videos on the following page: https://arnoldservice.com/air-conditioning-heat-pump-troubleshooting-questions-answers-index/ We also have an air conditioning and heat pump troubleshooting simplified page that I hope will help you find and fix the problem: https://arnoldservice.com/air-conditioning-heat-pump-troubleshooting-simplified/ We also have lots of troubleshooting advice on the following page: https://arnoldservice.com/troubleshooting/ If you have any specific questions please let me know. I hope you have a great day! Steve

  4. Hey all,
    I have had a history of problems with my AC and the electrical side. The breaker blew last summer and I ended up updating my electrical box. I am not sure the electrician set things up correctly. My fan works but the AC doesn’t. When it is set to off, I have 1.1 volts going to it while when cool is turned on I show zero. I can’t figure out why. Thoughts before I call the electrician (it’s only been about 5-6 months so he may not charge me if I’m lucky)

    1. Hi Josh! Sorry to hear that you are having problems with your AC not working! I would suggest that you go to your Air Conditioner’s breaker and turn it all the way off and back on again. If this does not fix the problem then I would suggest that you call the electrician or HVAC company back to see where the problem is located. Sorry that I can not give you much advice. I hope you get it fixed soon! Steve

  5. New furnace installed yesterday. Installer swapped intake and vent lines. inducer intake comes from roof now and exhaust is horizontal through the side of ny house. Called him to let him know and was told this is not an issue.
    There is 27 years of exhaust grime inside the vent pvc, do I really want that on the “fresh” intake?

    1. Hi Tim! Most high-efficiency furnaces that are vented with PVC pipe produce water and pretty much clean the plastic vent pipes. The only reason for the PVC pipe to get dirty would be if the old furnace had a crack in the heat exchanger, or a poor burn and allowed suit and black dirt to build up inside the vent pipe. It really should not matter if the vent and intake are switched unless you see that the pipe is really dirty, but like I say on most high-efficiency furnaces the vents are pretty much self-cleaning. I hope you have a great day! Steve

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