Nest Rheem Heat Pump, E73 error when using Aux Heat
Hello,
My dad and I just installed a Nest thermostat at my parents house just after Christmas and everything appeared to be running fine, until this week when some snow/colder weather hit. It was up around 60/70 degrees during Christmas and New Year's so the heating was barely turned on. Running a test on everything worked just fine.
It is a Rheem heat pump system, the wiring is setup with a Y1, G, O/B (set to B for this unit), Rc, W2/Aux, C, and \* (emergency heat) wires. The Aux and the Emergency heat are wired together at the heat pump as that's the way it was with the old Honeywell Thermostat.
The issue we are having is now that the temperature has been dropping into the 20s at night, the heat pump is running almost constantly, which is normal at those temperatures, once the Nest realizes the heat pump is not raising the temperature, it is turning on Aux heat, again, this is the correct behavior, however at some length of time I've been unable to determine, when using the Aux heat, the Nest will get an E73 power error. I suspect something on the heat pump end is cutting power and the issue is not actually with the Nest itself or wiring, but we can't seem to figure this out. This problem only happens in the mornings when it's cold (2/3 degree difference) and trying to heat back up, throughout the afternoon when it's been closer to 40 outside, the Aux heat will still sometimes be engaged, but it will heat up the house, turn back to regular heat and not lose power, behaving properly. The first time this happened, we had a snow storm overnight and the power was flickering throughout the morning so we figured it was that, now it's still happening days later even though the power is fine.
None of my searching on E73 errors have turned up anything like this. I'm also thinking it might be low on freon, which is why the heat pump is struggling so much by itself, but I still don't think that would explain the random power loss.
