my system has forced water radiators as well as an AC unit in the attic with fan/compressor outside (but not a heat pump to my knowledge).
Changing my main zone to the nest and uncovered this wiring from prior Honeywell thermostat (which oddly used a blue wire in a green slot). When installed, turning on the heat now triggered the outside fan as if it was a heat pump. In addition there was no power to RH so the nest shut down after the battery ran out.
anyone have a similar issue and solution?
Any spare unused wires in the cable that comes from the AC system?
If you can get a C wire connected at the Nest, and also at the AC unit, it will work correctly and only use the power from the AC system.
Thank you for the help. The 3 wires that come out from AC unit I believe are the Red hooked into RC, a blue and a green. All 3 were hooked into slots in prior thermostat and I don’t see any extras.
You must have set it up wrong and it thinks you have hot air furnace.
Set it up as a dual fuel system.
Tell it heat is radiators and Ac is forced air.