I have a zoned HVAC system that uses a Honeywell control board(see below) and dampers for zoning. If I set the upstairs thermostat to call for cooling, it will cool for a while before suddenly abandoning cooling and turning the heat on. I set the thermostat to 77F last night and woke up this morning sweating to find the thermostat was STILL set to 77F but the room temperature was 83. I went downstairs and saw the actual furnace flame lit and the system light on the control board red(indicating heat).
So far, I've found the following:
- swapping upstairs and downstairs thermostats doesn't fix the issue(meaning it's not the thermostat doing weird stuff)
- calling for cool on the downstairs thermostat only seems to produce expected behavior (it cools to set temperature and then shuts off)
- calling for cool on upstairs and downstairs triggers this weird behavior, even if they're both set to the same temperature
- calling for cool upstairs only also triggers this behavior
The issue began when I removed the upstairs thermostat from the wall to re-seat it properly(whoever installed it hadn't used plugs so it was basically hanging off the wall). I drilled a couple of holes, put some plugs in and re-seated it on the wall. That seems like a coincidence but it felt worth mentioning