Heat pump circuit breaker blows even with thermostat off

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Old 02-04-15, 03:42 AM
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Heat pump circuit breaker blows even with thermostat off

The circuit breaker to my heat pump blows (and the lights dim) even though the thermostat is switched Off (neither Heat nor Cool).

I tested the capacitor as it's supposed to be a common culprit but both seem to charge up fine with the proper capacitance. The only thing that I noticed was that the fan side of the capacitor discharges quickly (down 50% in voltage in only 34 seconds) whereas the compressor side of the capacitor discharges slowly (down 50% in voltage in 3 minutes).

I'm now suspecting the contactor. And I'll check that soon when the weather gets a bit better.

With the thermostat off, is the contactor supposed to be activated or not? It doesn't seem to be.

Thanks in advance for your help. Still recovering from a car accident (car behind me was probably texting) so no money coming in right now to afford a repairman. Using the wood stove and electric heaters right now.
 
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Old 02-04-15, 05:11 AM
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The compressor Contactor should push in freely with the power off,that could be the problem especially when you notice the lights dim,sounds like a dead short,possibly the compressor,if you shut off the disconnect outside by the condenser can you reset the breaker?
Geo
 
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Old 02-04-15, 06:02 AM
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Thanks Geo for offering to help. It's appreciated!

It does sound like a near dead short. But it's not a complete short because it does take a few seconds to trigger.

I have fiddled with the arm of the contactor and it seems to move freely. There was no sign of heating or arcing. I'm going to have to do some wire tracing to see where the near-short is happening.

If the problem is the compressor, why would it be trying to engage it when the thermostat is off?

I'm not too sure what you mean by "shut off the disconnect outside by the condenser". There are no switches inside, unless you mean to disconnect the condenser to see if the condenser is shorting?
 
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Old 02-04-15, 08:55 AM
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Welcome to the forums.

Most compressor's used for heat pump operation, especially in colder areas, have a crankcase heater. That heater is thermostatically controlled and operates without the contactor activated.

I'd check that first.

It could be a silver band around the bottom of the compressor.
 
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Old 02-04-15, 09:42 AM
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To add to Pete's theory of a possible bad crankcase heater, the presence of a crankcase heater would also be indicated by two wires coming out of the lower part of the compressor. These wires would go to the incoming side of the contactor.
 
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Old 02-04-15, 09:53 AM
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The disconnect should be outside near the condenser,but if you say the contractor is free,the crank case heater as mentioned could be the culpert,it is energized all the time except when the compressor is running,shutting off the disconnect would isolate any problem with the condenser,if the breaker resets that would pretty much indicated a problem in the condenser.
Geo
 
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