Control of home air exchanger (timed make-up air control) with cheap thermostat


#1

I see there has been some discussion around air exchangers, whole house fans, etc on the forums. While this is not strictly a smart things type question I figured I’d pose it here anyway.

I have a whole house air exchange system controlled by a TROL-A-TEMP TMAC II (I swear I didn’t make that up) It’s a combo mechanical electric timer that opens an external damper, and integrates into the hvac system to turn on the furnace fan.

The system uses 24 volts, and I can’t yet tell if it has it’s own transformer or if it uses the furnace 24 volts.

My thought is to use an inexpensive thermostat and smartthings/ifttt/etc to control turning it on and off.

I’m going to get the multimeter out and take a closer look at the wires and what is happening in idle and active mode.

I am thinking 24 volt power to the thermostat as normal, and then hook the damper to the AC on/off, and hook the standard fan control wires to it as normal. Set the AC to something like 50 degrees so whenever the system is turned on, it will meet the criteria to put 24 volts out to what would normally be the AC contactor.

Does anyone see glaring problems with this? You can get some really inexpensive wifi thermostats, and it’s easier (possibly even cheaper) than building a raspberry pi for this purpose.