Flaky Furnace Thermostat

CarnationSailor wrote:
OK, I'm ready to give up on finding the cause of the tstat resetting. I am think of installing a mechanical, 2-wire thermostat next to the existing tstat, but I want to be sure to wire it up correctly.

The existing tstat is supplied with 12-volts via a red wire and there is a white wire that is labeled "Furnace" in the tstat manual. My assumption is that the white wire supplies 12-volts to the furnace whenever the tstat calls for heat.

Leaving the red wire connected to the existing tstat, I plan on tapping off the red wire to provide 12-volts to the new tstat. Then I would disconnect the white wire from the existing tstat and connect it to the new tstat.

Sound like the right way to do it?

Thanks

I quoted my plan above just to refresh everyone's memory.

Well, I finally got around to executing my plan, and it worked perfectly - AFTER I bought a compatible tstat. According to Honeywell, the CT87K was not going to work in a 12VDC system. (It was designed for a 24VAC system.)

I exchanged the CT87K for a CT53K which is about as old tech as you can go. Completely mechanical with the old bi-metallic coil.

So now I have two tstats mounted side-by-side: the OEM which controls only the Air Conditioner / Heat Pump, and the CT53K which controls only the furnace.

I would have preferred to solve the original problem without having to use a workaround, but tracking down why 12VDC to the tstat was being interrupted was beyond my knowledge level.