"HVAC - Compressor Unit Tripping Circuit Breaker"
By Ron Stultz
1 August 2014
Summary: most likely compressor has developed an electrical short in the motor or has locked and will have to be replaced BUT....confirm if you can.
Background:
Daughter's home.
Original, 10 year old, Carrier 2.5 ton compressor unit outside.
Suddenly, hot air blowing out vents.
Compressor or unit outside, has tripped the circuit breaker.
Upon reset of circuit breaker for compressor (240 volts alternating current, 30 amperes), immediate trip of breaker again.
Possible causes of outside unit tripping circuit breaker:
- Compressor motor has developed an electrical short. An electrical short can happen if the compressor gets too hot and the built-in thermal protection breaker fails.
- A faulty circuit breaker. (Never have seen a faulty circuit breaker and I have seen many, many, breakers.)
- A wire in the compressor unit has come loose and is shorting to the cabinet.
- The fan motor on top of the compressor unit has developed an electrical short.
Warning: HVAC AC uses 240 volts AC which can kill you. If you have never worked around high voltage, do not attempt a self diagnosis.
Do it yourself (DIY) diagnosis:
Make sure breaker is off to outside compressor unit.
Turn off breaker for house air handler. The air handler is the blower unit inside the house. This could have a separate breaker or could even be on some room circuit. It may also have an "emergency" cutoff switch near the blower unit.
Pull quick disconnect that should be right beside the outside unit attached to outside house wall.
Where pipes enter the compressor unit, find screws holding cover over one corner of unit and remove.
Visually examine wires for burns or loose wires. Is possible short is right in this area of compressor unit.
If wires or terminals look bad or even broken, need to replace or have HVAC repairman replace. Note here, do not touch any terminal or wire until you have take a volt meter to all terminals and confirmed there is no voltage on anything!
If no visual signs of damage to wires, unbundle all wires to determine which wires go inside to the compressor motor and which wires go to the fan on top of the unit.
There should be 3 wires going inside the unit for the compressor. Trace them back and you will find they probably are connected to the 2 top terminals of the "contactor" or thermostat controlled relay. When the thermostat clicks on to demand more cooling the contactor relay is closed making a high voltage connection to the compressor motor and motor on top of the compressor unit.
Remove the 2 wires going to the compressor motor from the contactor terminals. AGAIN, make sure these wires are dead, dead before touching.
With compressor motor unhooked from contactor and compressor wires either taped over or in such a position that they can not contact either the metal of the compressor shell or any other wire, make sure the contactor top 2 screws are tight.
Now reinstall the quick disconnect.
Go into house turn back on blower unit and set thermostat to temp below ambient room temperature.
Now flip breaker for outside compressor unit. If it trips immediately, then the fan motor on top of the unit is bad and must be replaced.
If when you flip the outside compressor unit breaker it does not immediately trip, then the compressor is bad and must be replaced.
Now flip compressor breaker back to "off".
Turn "off" inside air handler.
Go back outside and pull quick disconnect.
Reinstall compressor wires on contactor.
Put cover back over corner of compressor unit.
Final note:
Besides a short in the compressor motor or a short in the fan on top of the unit, there could be other issues causing the breaker to trip.
SO, in the end, recommend service man call.