My wife and I just bought a house and I was thrilled when I saw that the outside unit was a heat pump (a Goodman ck36-1b model, to be exact). Well, today was the first day that we were to run the heat, and I noticed that the furnace kicked on immediately. "Strange," I thought, "doesn't the furnace turn on as a secondary stage?" Well, a good amount of time goes by, and I'm starting to feel quite flushed. The temperature is over 80, and I had the thermostat set at 68. I pulled the thermostat apart, noted the function of each wire, then crawled into the attic to confirm the purpose of each wire. The previous owner's HVAC guy / gal had done something quite odd. First, the thermostat does not do two stage heating. It can handle a heat pump or a furnace. Second, he / she had some strange wire issues. The W wire (which is actually blue and may have caused the confustion) was attached to the change over receptacle (thus why the heater was not turning off). Thankfully, the connection between Y and W were not jumpered on the thermostat, as both the heater and AC would have been running. There was also a white wire that was attached to the W receptacle. Convinced that this white wire was the change over wire, I went to the Home Depot and purchased a thermostat that accepts two stage heating (a RiteTemp 8050c). When I get the new thermostat home, I wire up each system independently to test it out. The heater wired up in solo mode worked fine, but when I hooked up the heat pump with that white wire I was convinced was the change over wire, what happened but the vents start pushing out frigid air. After much swearing, I crawled back into the attic. If I would have taken careful note the first time, I would have noticed that the white wire was probably an old common, and was present in the attic, but not connected to anything. Furthermore, the wires going to the heat pump unit are red, yellow and green. I know what the red and yellow wires are, and I'm fairly certain about the green wire (ground, I imagine, but it, too, is not hooked to anything; its just sitting up in my attic with an exposed end). I have yet to access the service panel of the heat pump, but my question is how easy would it be to add a change over valve signal wire to the heat pump, run it into my attic and connect it to that "spare" white wire? Is this something a relative DIY newbie could do with the assistance of his veteraned father-in-law? Or is this something that a nitty-gritty HVAC person has to tackle? Sorry for the long-windedness, but I was being as thorough as possible in my description of what I know.

If this is a single story house, it should be fairly easy to fish a wire up through the interior wall the thermostat is on to the attic. From downstairs in a 2 story house, could be difficult without knocking holes in the drywall.

How many wires do you have, and is the thermostat a heat pump thermostat? The green wire is not a ground, but usually connects to the high speed blower relay used with A/C and fan on. Blue is often a common only needed by some thermostats for their power. I think you need to study the system some more. There may be some logic to automatically switch between the furnace and the heat pump at the furnace.

If nothing else, this answer will bump this up to where Northern Heat will see it now he is back. .

At the thermostat G-green wire blower, Y yellow compressor, O-orange reversing valve(if its not an older Rheem heatpump), W-white aux heat (heat strips), C is common use any wire left over if needed. Your thermostat needs to be two stage heat and one stage cooling.