When Your AC Compressor Won’t Turn On: What To Do Next To Fix It

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The air conditioning compressor is the heart of the A/C system and can be a real headache if not working properly.

Many things could cause a compressor to malfunction.

Here is a list of some common problems to check out when troubleshooting a device:

Start Run Capacitor Is Kaput

The compressor won’t start up if the Start Run capacitor isn’t good. It needs to be replaced if bad.

Testing the capacitor is easy enough with an HVAC multimeter.

They’re also low-cost parts to replace.

Condenser Fan Motor Failure

ac compressor not running

If a bad condensing fan motor prevents a compressor from working, it will not function properly.

This can also be related to a bad capacitor because Start Capacitors can start the condensing fan motor.

If the fan motor fails, the compressor will kick on briefly before stopping when the head pressure builds up.

Since the heat isn’t dissipated away from the heater, the amps and heat will build up, causing the motor to overload and trip off.

The compressor will turn on and cool down if the device is turned on. It will then start up again, which will cause it to run for a short time, heat up, and kick off.

Often, an air conditioner gets loud when this problem occurs.

This could potentially damage your compressor because the pressure can get high and draw a lot of amps.

Bad Contactor or Relay

ac compressor not running

A relay or contactor controls the key high 220 volts coming into a device.

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

A low-volt voltage thermostat is used to trip a connector that lets 220 volts power the device.

Common problems include pits or the relay coil winding up running incorrectly.

Bad Thermostat

If there’s a problem with the thermostat, it won’t start.

Make sure the thermostat is turned on and set at a low enough temperature for the device to be able to turn on.

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

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

The circuit breaker should pull in on the main panel powering when the red and green wires are jumpered.

Electrical Short

ac compressor not running

If the winding on your compressor runs terribly, it may cause the unit to ground out (or short circuit).

When this happens, the breaker will throw. It can occur for various reasons, like an insect getting into the device or the compressor.

Float Controls

AC units will need to drain water if it’s humid outside. Float controllers can shut down a unit if the drain hose or pan becomes clogged.


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

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

Of course, it can only have a mechanical failure and quit working. If you’ve encountered issues, let us know in our comment section. Overload and trip off.

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