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  1. #1

    Question on the operation of Aux heat

    I have a 2400 sqft house that uses two Goodman heat pumps. I bought the place two years ago and the systems were installed by the previous owner before they moved. Below are the model numbers as listed on the equipment. When it gets cold out, below about 18 degrees, the thermostats will switch to aux heat. When this occurs, you can hear a click at the thermostat. However, the air stream does not feel any warmer. As an experiment I put one of the units into emergency heat. When I did this the outside compressor turned off and the air stream was immediately warmer. As a test I measured the current to the air handler. In normal heating it pulled 0.7 amps, which I suspect is the blower load. When the thermostat called for aux heat, the current reading was the same at 0.7 amps. When the unit goes into a defrost cycle, the current reading jumps to 42 amps. As soon as the defrost ends, the current drops back to 0.7 amps, even though the thermostat is still reading “aux heat.” If I put the unit into emergency heat, the current reading jumps to 42 amps. Additionally, if it gets cold enough, the units will drop below their set points, while in aux heat. The lowest I have seen was 3 degrees below the set point. I checked the CPH settings and found that both thermostats are set to: “aux heat” = 5, “emergency heat” = 9, “compressor” = 3.

    It seems to me that even though the thermostat is calling for aux heat the heating strips are not turning on. However, the heating strips will turn on if I force the units into emergency heat or the units go into a defrost cycle. To me, this doesn’t make any sense. I can’t understand why the thermostats would list aux heat, yet the heating strips are not turning on. In searching the web, I found some comments that aux heat won’t start until the thermostat drops to 2-3 degrees below the set point, but why would the thermostat say “aux heat” when it is not on at that point. Does this behavior seem normal?

    1st floor system
    Thermostat: Honeywell Pro TH3210D
    Compressor Unit: GSZ130241AB
    Air Handler: ARUF182416BA
    Heating Kit: HKR-10

    2nd floor system
    Thermostat: Honeywell Pro TH3210D
    Compressor Unit: GSZ130301AC
    Air Handler: GSZ130301AB
    Heating Kit: HKR-10

  2. #2
    Join Date
    Apr 2011
    Location
    SE Washington
    Posts
    559
    no its not normal, it could be that 2nd stage (aux) heat is not wired in to operate properly, have a technician come out, easy fix!
    Total Energy Management, inc

  3. #3
    Join Date
    Aug 2012
    Posts
    2,755
    Don't try rewiring yourself though you could cause more damage or even some shock therapy.
    My name is TooCoolforschool and I am a chronic over charger.

  4. #4
    Hi All

    I had a tech come out and look at it. He said that the thermostats were not wired correctly. The wire that was supposed to connect to aux heat was connected to "heat pump reset". The guy said this is why the heat strips would work in emergency heat but not in aux heat. The aux heat is operating correctly now.

    Thanks All

  5. #5
    Join Date
    Apr 2010
    Location
    NC Sandhills
    Posts
    412
    Tstat doesnt call for aux heat untill it gets to 18 deg outside, I have been underestimating them, in colder climates. Looks like your units are oversized for a/c but I bet you electric bill isnt to bad not having used that 20kw of back up heat in 2 years. Anyway glad it all worked out.

  6. #6
    Yes I believe that the system is oversized for A/C. I have heard that this is an issue with single stage heat pumps. If they are sized to minimize the use of aux heat in the winter, they will be oversized in the summer. From what I have read, the multi-stage heat pumps are much better at achieving both goals and some of the mini-splits on the market can deliver rated capacity below 10 degrees, which is amazing.

    My 2nd floor system also serves the family room on the 1st floor, which is open to the kitchen. I have found that I can just run the 2nd floor system alone in the summer and it will properly cool the majority of the house. (In a major heat wave the living room and dining room might be a 1-2 warmer.) If it bothers me, I run the 1st floor system as well.

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