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  1. #1
    Join Date
    May 2007
    Location
    DC Metro Area (MD)
    Posts
    3,368

    Defrost Cycle and VisionPRO Thermostat

    With a head pump defrosts and is controlled by a VisionPRO thermostat (TH8320U1008 in this scenario), should the thermostat display "Aux Heat On?" Mine does not, but the air coming out of the registers isn't really cold, it's more in the 70 degrees range. I don't even think it makes a click, but perhaps the W wire goes right from the ODU to the AHU; I don't know. I had a service tech check over the wiring for the thermostat. Does this sound normal? Thanks!

  2. #2
    Join Date
    Mar 2004
    Location
    Grottoes VA
    Posts
    5,856
    The thermostat has no idea whether your Heat Pump is in defrost or not.
    Karst means cave. So, I search for caves.

  3. #3
    Join Date
    Feb 2008
    Location
    Florida
    Posts
    143
    Quote Originally Posted by RyanHughes View Post
    With a head pump defrosts and is controlled by a VisionPRO thermostat (TH8320U1008 in this scenario), should the thermostat display "Aux Heat On?" Mine does not, but the air coming out of the registers isn't really cold, it's more in the 70 degrees range. I don't even think it makes a click, but perhaps the W wire goes right from the ODU to the AHU; I don't know. I had a service tech check over the wiring for the thermostat. Does this sound normal? Thanks!
    If the heat pump back feeds w to the t-stat when it's in defrost mode this will have no effect on the aux read out on the t-stat. But you will read 24 to 28 volts between w and c at the t-stat, also because the t-stat must be calling for elec. heat if it reads aux.

  4. #4
    Join Date
    Aug 2004
    Location
    North Richland Hills, Texas
    Posts
    14,914
    The "Aux heat" display on the Vision Pro thermostats only shows up if the thermostat is calling for aux heat, so won't come on during defrost, even though the heat pump should be sending 24v to W2(Aux) on the thermostat through where they both connect to the indoor unit.
    If more government is the answer, then it's a really stupid question.

  5. #5
    Join Date
    May 2007
    Location
    DC Metro Area (MD)
    Posts
    3,368
    Thanks guys, that's all I needed to know.

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