Reasons an Air Conditioner Compressor Will Not Start

By | June 5, 2020

Reasons an Air Conditioner Compressor Will Not Start
An air conditioning compressor is the heart of an A/C unit and can be a real problem if not working.

There are many things that can cause a compressor to stop working.

Below is a list of some common issues to look for when troubleshooting a unit.

Five Reasons an Air Conditioner Compressor Will Not Start

  1. Start Run Capacitor
  2. Reasons an Air Conditioner Compressor Will Not Start Capacitor
    A bad HVAC Start or Run capacitor will not start a compressor and will need to be replaced if bad.

    Testing the capacitor is easy enough with an HVAC multi meter. They are also low-cost parts to replace.

    Read Here for how to replace an HVAC start Run Capacitor.
     




     

  3. Condensing Fan Motor Failure
  4. Reasons an Air Conditioner Compressor Will Not Start Condensing Fan Motor
    A bad condensing fan motor will stop a compressor from working. This can also be tied to a bad capacitor since Start Run capacitors are used to start the condensing fan motor.

    When the Fan motor goes bad the compressor will kick on for a short while then stop when the Head Pressure builds up.

    Since the heat is not dissipated away from the unit the Amps and heat will build up making the compressor overload and trip off.

    If a unit is left On the compressor will cool down and kick back On, going into a bad cycle of running for a short while, over heating and kicking off.

    Read Here for How to Replace a Condenser Fan Motor.

    Often an Air Conditioner becomes loud when this happens.

    This could potentiality damage the compressor since the pressures can get high and pull a lot of Amps.

  5. Contactors or Relay
  6. Reasons an Air Conditioner Compressor Will Not Start contactor
    The contactors or relay controls the main high 220 volts coming into a unit.

    It uses a low-voltage contactors relay to control the high voltage which can go bad and not allow any voltage through.

    A low-voltage thermostat is used to trip a contactor which allows 220 volts into the unit powering it on.

    Common problem include pitting or the relay coil winding itself going bad.

    Read Here for How To Replace Contactors or Relays.

  7. Thermostat
  8. A bad thermostat or thermostat-wiring will causing a unit not to start.

    Be sure to check the thermostat is set on cool and at a low enough temperature to turn on the unit.

    HVAC techs often use a jumper wire to trip the unit on were the thermostat wires go into the system.

    For example, most air conditioners use the yellow wire to cool and red as the 24DC hot wire.

    When the yellow and red wire are jumpered the unit should pull in on the contactor powering on the unit.

  9. Electrical Short
  10. If the winding on the Compressor goes bad it will cause the unit to ground out.

    The breaker will throw when this happens. It can happen for many reasons such as a small bug got into the unit and the compressor wiring or simply age.

  11. Float Controls
  12. All A/C units need to drain water when it is humid. If the drain pans or hoses become backed up float controls can turn a unit off.

Summary
The above are a few of the main problems an HVAC air conditioner or heat pump unit can have.

Each component will need to be tested to find the problem and be replaced.

It can of course simply have a mechanical failure and stop working. If you have run into problems let us know in the comments below.



 




 

4 thoughts on “Reasons an Air Conditioner Compressor Will Not Start

  1. James L Cue

    I am having problems with my AC compressor not coming on. I changed the 2 fuses out, checked the power to the fuse box (got power to the AC), and cleaned off the fins (LOTS of cottonwood seeds!). I hear it click but the fan does not come on. Am I missing something?

    Reply
  2. Erick

    Questions? If a condensing coils is dirty how will it affect the operation of unit? And if an evaporating coils is dirty how will affect the operation unit. Can you please helping me with this two questions

    Reply
  3. shuaibu abdu

    My 2 HP remote controlled window unit’s when plucked plucked to power will not start. The fan starts and run speed controlled normal by remote control but when mode is changed to cooling , the compressor will not start. The compressor however run briefly when connected to the power directly. What should I do.

    Reply
  4. Jerry chancy

    Outside unit top fan comes on but compressor does NOT.
    Repalced capasitor and power is to compressor. Was
    Cooling fan and compressor off during night.
    I have hosed out and clean.

    Reply

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