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ac compressor won t turn on

What To Do When Your AC Compressor Won’t Turn On

The Air Conditioning compressor is the heart of an A/C unit and can be a real problem if not functioning.

Many things could cause a compressor to stop functioning.

Below is a listing of some common problems to look for when troubleshooting a device.

Reasons an AC Compressor Will Not Start

Start Run Capacitor

ac compressor not turning on

A bad Run capacitor HVAC Start won't begin a compressor and will have to be replaced if bad.

Testing the capacitor is simple enough with an HVAC multimeter. They're also low-cost parts to replace.

Condensing Fan Motor Failure

A bad condensing fan motor will prevent a compressor from functioning. This can also be tied into a bad capacitor because Start Run capacitors can begin the condensing fan motor.

When the Fan Motor turns bad, the compressor will kick for a short while then stop when the Head Pressure builds up.

Since the heat isn't dissipated away from the unit, the Amps and heat will build up, making the motor overload and trip off.

If a device is left on, the compressor will cool down and again turns on, going to a terrible habit of running for a short while, overheating, and kicking off.

Often an Air Conditioner gets loud when this happens.

This could mean potentiality damage the compressor because the pressures can get high and pull a good deal of Amps.

Contactors or Relay

ac compressor won't start

The relay or contactors controls the key high 220 volts coming into a device.

It utilizes a low-voltage contactors relay to control the high voltage that may go wrong and not let any voltage through.

A low-voltage thermostat is utilized to trip a connector that allows 220 volts to the device powering it.

Common Problems include pitting or the relay coil winding itself running wrong.


A bad notebook or thermostat-wiring will cause a device to not get started.

Make sure to examine the thermostat is set on cool and at a low enough temperature to turn on the device.

HVAC techs often use a jumper cable to trip the device where the thermostat wires go into the system.

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

When the red and yellow wire is jumpered, the device should pull in on the system's contactor powering.

Electrical Short

If the winding on the compressor runs terrible, it will get the unit to ground out.

The breaker will throw when this occurs. It can occur for several reasons, like a little insect got into the device and the compressor.

Float Controls

A/C Units will need to drain water when it's humid. If the drain hoses or pans become backed up, float controllers can turn off a unit.


The above are some of the critical issues an HVAC air conditioner or heat pump unit can have.

Each component will have to be tested to locate the issue and be replaced.

It can, of course, only have a mechanical failure and quit working. If you have encounter Issues, let us know in the comments below.overload and trip off.

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About the Author Tom Hanson

I’ve worked as an HVAC tech in Phoenix, AZ for the past 10 years. I created to help home owners select the right portable air conditioner, cooler or air purifier for their needs & budget in just a few minutes.

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