Heat Pumps and Electric Heating - Trane Heat Pump won't stop running.

This is a 17 y/o Trane heat pump. After the room temp reaches the target, sometimes, not always, the outdoor unit (compressor or cooling fan, or both, I don't know) could keep running with an annoying buzzing for up to hours. I can only stop it by:

1. putting the thermostat switch to "off";

2. putting the switch to "heat" and back to "off";

3. putting the fan switch to "on" and back to "auto"; or, when all the above don't work

4. waiting until it stops when it wants to stop.

This happens to both "heat" and "cool" modes.

The thermostat is a new TempRite, which should be trouble free.

Did this start happening after the new stat was installed ?

1. If the outdoor compressor runs and not the outdoor fan or vice versa, than I'd suspect the controls/ wiring at the outdoor unit.

2. Since fiddling with the thermostat seems to be able to have such an effect in so many different ways:
- either the thermostat is defective
- the thermostat is misswired or a wire is broken or loose
- the wires at the thermostat are accidentally shorting to the signal for the compressor.
If I had to guess, I'd go with a defective thermostat. Some thermostats even get flaky if the batteries are low, so check that too.

The 24 volt power source for the thermostat is typically generated at the indoor unit - if this is true for you, then you can disable the 24 volt control source by just shutting off the power to your indoor unit ... typically the indoor and outdoor unit are on different circuts.
If you shut off the power to the indoor unit and the buzzing continues, then chances are there is a wiring fault in the outdoor unit.

If you want to investigate the thermostat, try removing the cover of the thermostat - it usually pops off with slight prying (with a coin or small screwdriver) - and look at the wire connections to the thermostat - wiggle each wire to make sure it is securely connected, make sure that no two wires (the bare copper part) are accidentally touching.
If the thermostat has a reset button, press that for good measure.

3. To decide if the thermostat is defective: when you have the "buzzing" , disable the thermostat thus:
In the thermostat you will probably see a red wire connected to a terminal marked "R". This is the 24 volt power source that the thermostat directs to the other wires to activate the various functions, so if you disconnect it, then everything should go off, the outdoor unit should get no signals, so it should just sit quietly. This red wire is probably connected at a screw terminal - just carefully loosen the screw, pull the wire out, being careful not to touch the bare end to any of the other terminals . If the "buzzing doesn't stop, it's not the thermostat.

4) It's easy to imagine that the outdoor unit wiring or controls are failing somehow. Either the outdoor unit is running completely on its own, or its running because it's receiving a signal from the thermostat - or because there is a short in the wiring somewhere. If you've not been able to stop it by shutting off the indoor sources of 24 volt signals then chances are that there is a bad relay that is sticking or some other electronic fault in the outdoor unit . If you're adventurous, you can remove the outdoor unit access panel and take a look; eyeball the wiring and the circuit board or relays -look for junk or charred components or loose wires ... just be sure to turn the POWER OFF to the outdoor unit first - there is lethal voltage AC power to beware of !!! There should be a shutoff switch within sight of the outdoor unit - turn that off - and for good measure turn off the power at your main circuit breaker panel too !! --- if this makes you uneasy, stop now.

good luck.

This also happened to the old thermostat. That's why I changed it 'cause I thought it's out of order.

RiteTemp offered an exchange for free, but the problem's persisted.

Thank you idler for your message.

I don't think it's the stat becuause it's new and this also happened to the old stat. I checked the outdoor unit once before and nothing seemed wrong.

Anyway, I will check the system again as you suggested.

Thank you so much.

You have a bad compressor contactor in the outdoor unit. replace it.

You have a bad compressor contactor in the outdoor unit. replace it.

I disconnected the "R" wire and the buzzing/outdoor unit did go off.

So, is it a defective thermostat or a bad compressor contactor?

Hook it back up. Run the unit then turn it off at the thermostat. Go to the outdoor unit and see if it continues to run. If yes, check for 24 volts at the compressor contactor magnetic coil. If you read 24 volts, problem is ouside the unit. If you do not read 24 volts, the contactor is stuck closed and needs replacing.

Removing the "R" wire interrupts any control signal from the thermostat. Since doing so stops the "buzz", it would appear that the buzz is because of the outdoor unit (compressor contactor eventually) receiving a 24V signal from the thermostat.

The compressor signal wire is probably labeled "Y" at the thermostat - when you expect the system to be off, yet it's buzzing, remove this wire at the thermostat to see if the buzz stops. If so, the thermostat is incorrectly routing the 24V to the "Y" signal.

The trouble shooting is much easier with a voltmeter: do you have one ?

The system wiring at the thermostat could also be wrong ... I observe that RiteTemp provides lots of wiring details on their web site - have you checked there to see whether you are using the appropriate thermostat, and that it is correctly wired ?
What is the model number of your RiteTemp thermostat?

You've yet to mention whether the outdoor fan also runs or is it just the compressor that buzzes.


I disconnected the "R" wire and the buzzing/outdoor unit did go off.

So, is it a defective thermostat or a bad compressor contactor?