Back in the day, we had an "anticipator" setting in the thermostat to match the setting number in the furnace manual. This setting helped compensate for the startup time until the heat exchanger was hot and the blower came on and the run time after the fire was out to cool down the heat exchanger. That was supposed to keep the temperature swings plus or minus one degree of the set value.
That concept worked some of the time, especially if the furnace and thermostat were branded from the same manufacturer.
I wonder if both A/C units in a dual installation have the heat pump functionality? I may get that answer when our unit is completely built, delivered and I have access to the manuals.
The comment above about sealing the wire hole behind the thermostat going into the refrigerator space is a good start. Perhaps a thin insulator pad between the wall and the back of the thermostat would also help prevent mis-information being input into the thermostat enclosure from the wall itself?
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