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We have

  • T874G1196 thermostat by york (can only find honeywell documentation)
  • MB7BM-1200K-B air handler
  • H8HK015H-21 electric heater
  • Thermopump (heating and cooling)

We want to connect it to a nest thermostat E.

We have 7 wires to connect to the nest. This is a picture of our current thermostat wiring. enter image description here

I spoke with a nest employee via chat on their website and she seemed to say that our system was compatible only we would need to get a pro to come and "join the O and B wires into the "*ob" terminal on the nest". She also mentioned something about possibly needing a relay but was reluctant to go into detail as I felt she was worried I might mess up my system.

Before we go and blow a whole wad of cash for some guy to come and twist 2 wires together, I just wanted to get your opinion on our setup.

  • here is a description of the hvac wires ... highperformancehvac.com/thermostat-wiring-colors-code ........ it implies that O and B are the opposites in function, depending on the heat pump manufacturer ...... one type cools by default and requires a signal to switch to heating mode .... the other type heats by default and requires a signal to switch to cooling mode – jsotola Jan 3 at 3:14
  • Can you post photos of the wiring at the air handler, as well as the wiring diagram for your air handler? – ThreePhaseEel Jan 3 at 3:21

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