Help with Nest Thermostat wiring for Heat Pump; 2 wires on W2

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  #1  
Old 05-22-14, 08:42 AM
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Help with Nest Thermostat wiring for Heat Pump; 2 wires on W2

I am replacing my old thermostat with a Nest (2nd Generation). The wire setup looks good, except that the old thermostat had 2 wires on the W2 terminal (a blue and a white). The Nest only has room for a single wire.

I just picked one of the wires (the white one) and left the blue one unattached. The Nest works fine, except that it's giving me an error; N25, which means there's no power to the W2/Aux terminal.

Question:
Should I just swap out the white wire for the blue one? Also,
Why were there two wires on the W2 terminal for the old thermostat?
 
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Old 05-22-14, 01:45 PM
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Could you post the model number of your old t-stat?

I've read bad things about nest when used with anything but a basic gas furnace and a/c, but have no experience with it. Also, since you have backup heat -> you'll be better off maintaining a constant temperature than turning it up and down through a smart phone. Heatpumps and programmable t-stats don't mix, unless you make use of the hold feature.
 
  #3  
Old 05-22-14, 02:44 PM
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Carrier Heat Pump System Control -
Part with Mercury T874R 1384 / HH07AQ170
Part with wire connections Q674L 1454 / HH93AZ 197
 
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