Exisiting honeywell ct87A-4447-1 has 5 wires (r,g,w,y,b). the new honeywell RTH6400B only calls for r,g,w,y (no blue) wires. What do I do with the blue wire

Asked by paul on 10/31/2008 1  Answer

ManualsOnline posted an answer 15 years, 11 months ago

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2 The B wire is the call for heat changeover valve in a heat pump system. If you have a conventional heat system (gas or oil), tape it off and forget it. If you do have a heat pump system, you need either B or O call. Do not go by wire color. Make sure it was/is attached to B terminal on the old t-stat. Sanity check: see if the B wire is even attached to the heater/furnace (probably not).
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