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Old 01-31-2020, 03:54 AM   #1
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Thermostat Heat Pump Issue?


This is where I'm at:

A little over a week ago my thermostat stopped working. After looking into things I found my transformer went out. Got a new one and replaced, thermostat had power again. Tried using it - AC didn't seem to work, neither did heat, and fan never came on using either. I changed fan from 'Auto' to 'On' while still in heat mode. Came on for ~15 seconds then everything shut off.

Thermostat didn't come on after that even after resetting breakers. Thought I fried it... Well, another day I removed the thermostat and jumped the contacts manually. Fan works, A/C works, but as soon as I contact the O/B heat pump wire everything trips. Doesn't trip the breaker but power is gone across the board until I turn the breaker off and back on again.

Now, I've disconnected the O/B wire and can use the thermostat, only in heat mode though. Even then, it only does anything (seemingly just turns on the fan) when I set the 'heat' temp above the current ambient temp - like A/C.

From what I can gather it seems the heat pump is stuck in A/C mode. It is a Rheem unit, so I know A/C is the default and the valve energizes for heat mode. Additionally, I've checked voltage from the transformer to panel and all seemed okay. I disconnected the O/B wire from the transformer and checked again; no voltage between the thermostat and R. What got me is that testing voltage from R and O/B from the heat pump came back with 26VAC. Does this mean there's a short in the heat pump board, wires, or elsewhere?

If so, or if not, what are my next steps?
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Old 01-31-2020, 06:52 AM   #2
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Re: Thermostat Heat Pump Issue?


Do you mean your resetting the main breaker or the one for the transformer?
The O/B wire doesn’t run to the transformer.
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Old 01-31-2020, 06:54 AM   #3
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Re: Thermostat Heat Pump Issue?


The main breaker.
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Old 02-03-2020, 04:07 AM   #4
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More recently: I ran a 'test' wire from the thermostat to the heat pump (bypassing structural, pest, etc. concerns), thinking that there might have been a short somewhere along the line being why I got 24VAC even with wires disconnected. Somehow with the test wire I still get 24VAC when metering to R. I know there are a few options now after ruling out inlet wiring, transformer issues, thermostat down, etc. everything down to the heat pump. My question now is: does this seem to be related to the control board, coil, hp relay, or any better ideas?
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Old 02-03-2020, 07:19 AM   #5
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Re: Thermostat Heat Pump Issue?


How are you measuring voltage?
You should be testing across all devices and not to ground.
The voltage source comes from the transformer in the unit.
How is your new thermostat wired?
Honestly your issue doesn’t make much sense. The main breaker shouldn’t have a whole lot to do with a problem like this.
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