Help Needed Preventing Auxillary Heat

Discussion in 'HVAC Heating & Cooling' started by TKB4, Jan 22, 2021.

  1. TKB4

    TKB4 New Member

    Dec 2, 2018
    west tennessee
    I have a frigidaire/nordyne 3 ton inverter heat pump with natural gas condensing furnace backup. I recently Installed DIY Solar 12,600 watts with using it and batteries 80kwhr to run the whole house at least 80 % of the time most of the use is HVAC . This unit is upstairs and I have a downstairs geothermal unit with surestart that works great from the solar. My goal is to not allow the frigidaire unit to use the gas auxiliary heater. I am using the upstairs unit mainly to use excess solar power right now because the children are away at college. It does however take some load off the downstairs geothermal unit. The problem is it uses the aux gas when say upstairs temp is 60 and I want to se thermostat to 68. I adjusted the temp difference for thermostat to come on and I put the outside temp to not use electric to 12 degrees F. In observation just increasing thermostat 2 or 3 degrees from current temp Aux comes on. When the Aux is on it doesn't use the electric heat pump also so its acting like most units in Emergency heat even though it has an emergency heat setting also.Granted for Ac this wont be an issue. It has an IQ drive communicating thermostat with 4 wires that has to be used for this unit. Since the unit is available as pure heat pump and pretty sure same thermostat I think maybe changing install model to the one without gas backup may work and I can access the install menu. Right now its 036MG7 with the MG7 being the condensing gas backup.
    The model number is FT4B1-036k

    Even if I could just remove whatever wire at furnace portion tells it to come on might work but since electric doesn't aide the gas when just increasing stat a couple of degrees I am not sure it will.

    Any help or suggestions would be appreciated.
  2. fitter30

    fitter30 Well-Known Member

    Feb 2, 2020
    Retired service tech
    Peace valley missouri
    Thermostat have a emergency heat terminal that is used. That emergency terminal wire is going to the furnace. Disconnect wire put it in emergency heat shouldn't come on. Could put it on a outdoor thermostat set it at a temp you want it to be enabled.
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