Nest Thermostat 'W' wire connection

[RustyShackleford]

I have an old dual-fuel heat pump system. The "fossil-fuel kit" (which arbitrates between propane furnace and heat pump) appears to be failing. I want to replace my thermostat with one which is dual-fuel capable, and eliminate the fossil-fuel board. This will solve the problem, and makes sense as an upgrade, giving more control over the heating. I have acquired a Nest Thermostat E. I'm not sure how to wire it properly. In particular, I'm confused about the W wire.

I understand that it's used by the thermostat to call for auxiliary heat (if the outside temperature is too low or the set-point is much higher than the current indoor temperature) or for emergency heat (explicitly by the user). So this means I should connect it to the W terminal on the indoor furnace/air-handler unit.

But what about the W lead to the heat pump compressor ? My understanding is that it is an output signal from the compressor, indicating that it has gone into a defrost cycle. So do I just connect it to the W terminal on both the thermostat and the furnace/air-handler, so that all three W terminals are connected together ? Won't there be an electrical conflict between the thermostat and the compressor, since both are output signals ?

 

[fbelec]

not understanding what you are saying. but they are making a couple of different heat pumps now with a few different wiring. sometimes white should go to the compressor sometimes to the indoor unit, white is to call for heat white goes to the compressor and if it is to cold out for the compressor the white coming from the compressor to the outdoor unit to the indoor unit gets turned on for gas/oil/propane what ever the fuel to turn on that instead of the compressor. the new ecor thats the company name is wired just a tad different 4 wires go to the outside unit instead of 6. every thermostat and or unit is different where the blue or orange wire get switched to turn the reversing valve sometimes they liven up with cool sometimes the liven up with heat. your manual should tell you how it should be wired from the thermostat to the indoor unit to the outdoor unit.

 

[zrock]

Call your local heating company and have them come and install it... What you pay then for a hours work may save you much more in the end if you mess things up..

 

[Andrew Well]

With not much details provided, its hard to to tell how you should where your Nest thermostat.
If your 'dual fuel system' is a single stage heat pump and single stage furnace, then you should have a wire in the Y1 connecter and another wire in the W1 connector. Both the Y2( compressor relay stage 2) for the heat pump and the W2 (Aux heat) for the furnace are for the 2nd stage purposes. I hope this makes sense.

 

[RustyShackleford]

With not much details provided, its hard to to tell how you should where your Nest thermostat.
If your 'dual fuel system' is a single stage heat pump and single stage furnace, then you should have a wire in the Y1 connecter and another wire in the W1 connector. Both the Y2( compressor relay stage 2) for the heat pump and the W2 (Aux heat) for the furnace are for the 2nd stage purposes. I hope this makes sense.

Just saw this, thanks. I think I got it working right.

 

[Andrew Well]

Just saw this, thanks. I think I got it working right.

You are most welcome!