Posted on

Problem: Air conditioner or heat pump compressor will not start. Hear an UGGGG sound.

Happy AC

Problem: Air conditioner or heat pump compressor will not start. I hear an “UGGG” sound for 5 to 10 seconds when the compressor tries to start then the compressor shuts off.

Solution: When power is applied to the air conditioning outdoor unit the fan starts, but you hear a sound like the compressor is trying to start, “UGGG”…, for about 5 to 10 seconds and then all you hear is the outdoor condenser fan run. The compressor is locked and will not start. What is happening is the compressor is trying to start, but because the compressor motor being locked the compressor tries to start for a few seconds, and then because of the high amperage being drawn goes off on internal overload. The internal overload protects the compressor windings from overheating and burning up. I see this many times during the start of the air conditioning season. Some compressors just have a hard time starting after sitting all winter long. Some compressors are locked up so bad that I can not start them and must tell our customers that they need a new compressor or new air conditioning system. Many times I can get the compressor started again without having to buy a new compressor or new air conditioning system by using the device that we sell called, “Super-Boost.” I keep two or three of these on the truck. The compressor hard start boosters have saved many of our customers from having to buy new air conditioning systems. Please click here if you are interested in purchasing a Compressor hard start booster. I like the SPP6 that we sell. Please click here if you would like to see the SPP6 compressor hard start booster that we sell.  Compressors not being able to start can also be caused by a weak run capacitor. Please click here if you would like to see the Run Capacitors that we sell. We have same business day fast shipping! Please email us anytime if you have a questions or would like for us to look up and find out what capacitor your unit uses. Please send us your unit’s model number. Our email address is: support@arnoldservice.com. We would love to help you out and have your business! Below we have a good YouTube video produced by Grayfurnaceman which talks about hard start kits and how to install a hard start kit. I recommend the SPP6 (sold below) over the SPP6E compressor hard start kits.

SPP6 hardstartbooster

5 thoughts on “Problem: Air conditioner or heat pump compressor will not start. Hear an UGGGG sound.

  1. Hey Steve,

    I have a 5 ton Rheem CA and the ah will not come on in auto mode. It will blow in the on mode, but neither furnace or CU will come on. I can cool the house by manually pushing the contactor. The CU runs fine with contactor held.

    1. Hi Tom! Since neither the furnace or outdoor unit will come on in auto mode, I would think that you have a thermostat problem. The thermostat should send 24 to 28 volts to the fan relay on your air handler and outdoor contactor when in the Auto or Fan On mode. I would start with the thermostat wires and make sure you are getting 24 volts through the following wires when the thermostat is calling for cooling. (R) Red to Common, (G) Green to Common, (Y) Yellow to Common. If you are getting 24 to 28 volts between these wires when the thermostat is calling for cooling then the thermostat is OK. If not then you probably need a new thermostat. If you are getting 24 volts out of those wire combinations then continue to test between the Y and C (com) wires. Where you stop getting the 24 volts then this is more than likely where your problem is. You might have a low pressure or high pressure safety control switch out. I would suggest that you or you have someone check the refrigerant charge by attaching gauges to your unit. 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/ I hope you can easily find and fix the problem. Steve

  2. I have an HVAC split system that is about two years old. The condensing unit made an attempt to start, then immediately turned off, then a couple of minutes later did the same thing. I turned the unit off and tried again a few minutes later and it didn’t even attempt to start…no noise whatsoever.
    The system is Ameristar Model #M4AC4042C1000AA. My husband is very familiar with electrical wiring for a home and for an electrical panel, but has not worked on an HVAC system.
    Thank you for any help you can provide.

    1. Hi Mary! There are several problems that can cause an AC unit not to run. I would suggest that you start by making sure the unit has 220 to 240 volts going into the unit on L1 and L2 of the contactor. With the unit calling for cooling I would suggest testing between T1 and T2 on the contactor to make sure the contactor and contactor coil are working. I would suggest checking all connections to make sure they are all tight and make sure the unit’s run capacitor is in good condition. You might what to have the capacitor tested. We have an Air Conditioner Troubleshooting flow chart on the following page: https://arnoldservice.com/air-conditioner-troubleshooting-flow-chart/ and many troubleshooting problems with answers on the following page: https://arnoldservice.com/air-conditioning-heat-pump-troubleshooting-questions-answers-index/ I hope this will help you find and fix the problem. Steve

  3. I will be happy to try and answer any questions you have. Thanks so much for your interest and support in our website! Hope you have a blessed day! Steve

Leave a Reply

Your email address will not be published. Required fields are marked *