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aux heat comes on in cool mode

we have a system at the west moreland branch that is kicking the aux heat on when you turn it on. i am fairly new and am thinking it has to do with the reversing valve or maybe the thermostat itself. what should i check?


  • Zman
    Zman Member Posts: 7,447

    You are not giving us much to work with....
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • Check the thermostat terminal wiring

    Quite often, installers will wire (incorrectly) the supplementary heat to come on with the compressor in the heating mode. Depending on the thermostat, this can cause the heaters to come on the cooling mode as well. Make certain that there is one wire on the W1 terminal and one wire on the W2 terminal. If they are both on the W1 terminal, move the supplementary heat wire to the W2 terminal.

    Keep us posted.
  • Empire_2
    Empire_2 Member Posts: 2,343
    HP system

    Let's just say everything is wired correctly and now a problem seems to be showing itself as in heat cycles when calling for cooling.  Since most of HP systems are" fail safe heat", and upon a call for A/C the reversing valve should be energised (Term "O") causing the rev. solenoid to energise with the call for A/C.  That is the basic thing you should check for.  If you do not have that, there is either a problem with solenoid or the circuit itself. 

    Mike T.
  • Let's assume....

    The question was about supplementary heat coming on in the cooling mode. If the system is operating in the heating mode when calling for cooling, the reversing valve is a very likely place to start. However, as you mentioned, the supplementary heat (electric) is coming on.

    Are you certain that it is the electric heater coming on and not the heat pump operating in the heating mode?
  • Empire_2
    Empire_2 Member Posts: 2,343

    On a call for A/C "O" needs to be energised.  That will bring on the compressor, engage the reversing valve, and start the condensing unit fan.  Check you VAC at "O" and call for A/C.  If this circuit in calling, you should be cooling.  From there check your charge....When you check back, give us some pressure readings, volt and describe what's happening.

    Mike T.
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