A few months ago, my wife and I started sleeping with our bedroom doors closed to keep out our cat. We would wake up in the middle of the night to find our bedroom was very hot and it felt really hard to breathe. We got an Awair some time later and noticed the CO2 was shooting up to about 1500ppm within 2 hours.
To solve this, I began using the thermostat's "Fan" function set to ON to get ventilation continually throughout the night. My understanding is that this only blows air, but is separate from heating/cooling.
The problem is that even when we set our AC to heat or turn that system off, the fan appears to be cooling the house. Despite it never getting below 70°F outside, this fan function is getting the house down to 64°F within a few hours. Then, because I have the heat on to prevent it getting so low, the heat starts running.
I am running heating+cooling all night just to prevent from suffocating. Obviously our energy costs are out of control.
Am I misunderstanding something? Is it possible that thermostat is miswired such that the fan is hooked up to the AC itself? And how would I even begin to diagnose this?