@De35769 , When you have a wire inserted into Rh, and Rc the Nest Thermostat knows you have a separate heating system from a cooling system. You currently do not have C wire attached. In this case the Nest Thermostat attempts find a path to a power common using Y, W, or G wires. The absolutely best wiring is to have a dedicated C power wire. Understand this. Alternating Current power is just that. But if the heating transformer for the Furnace is wired opposite of the Air Conditioner air handler transformer, you likely have charging problems. Again, if you have a spare conductor wire you really should wire C to air handler C. Did you install a transformer in the heating system or does it have one from the manufacturer?
If this were my system, I would verify the wiring at the heater transformer. The transformer should have wiring label on it. It will indicate the supply power as Line and Neutral and load side as Power and Common or output might say Line and Neutral too. The Neutral is the Power Common.
At the transformer you need to ensure that between Power and Common wire or Power Wire and chassis ground, you have 24VAC +/- 4. I bet one of those transformers has Neutral and Line backwards or the thermostat wire is got R on Neutral. The only way to get this corrected is to use a voltmeter and verify from output of each transformer the wire is attached properly.
Again this is easy to do. Using a voltmeter, set the voltmeter to measure AC Voltage. Attach one lead to chassis/ground; something metal. The other voltmeter lead to the transformer output wire that R is attached to. If the AC voltage reading is zero or OL, it is wired to Common. Simply check the other transformer wire and you see 24 volts +/- 4. when you determine that, connect the R wire to it. Do this Test at each transformer.
Thr Cooling Wizard
Google Pro, Mechanical Engineer, Electrical Engineer and HVAC service company owner.
