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  1. #1
    Join Date
    May 2004
    Location
    Austin, TX
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    Wiring around heat pump defrost controls.

    I have a 1986 Rheem 1.5 ton heat pump. Unit still works but is stuck in heat mode when
    thermostat either calls for cooling, or heat pump. T stat is ok. Have not dug into unit
    yet to see if defrost board is bad, reversing relay is ok, as is changeover relay. Also
    reversing valve is ok.

    I was thinking of disconnecting all the defrost boards, and relays, and defrost sensor.
    Schematic says unit has a time, temperature defrost control.

    Was thinking of taking 24 volt wires from thermostat and direct wiring to relays
    to control contactor, and reversing valve.

    This unit is in central Texas where it rarely gets below 28 degrees, plus this unit is
    in a guest house in the country, so it is only used about 4 times a year. This is on
    a friends ranch, I stopped by to quickly look at for him.

    This guest house did have two Rheem heat pumps, but the second one developed
    a leak in the condenser, so I changed out that system for a new 1.5 ton unit with
    straight cool, and electric heat.

    Units are not used enough for the heat pump to pay for itself.

    Any one done this before?

  2. Likes rollandsaxton liked this post.
  3. #2
    Join Date
    Mar 2016
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    74
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    Quote Originally Posted by edward301 View Post
    I have a 1986 Rheem 1.5 ton heat pump. Unit still works but is stuck in heat mode when
    thermostat either calls for cooling, or heat pump. T stat is ok. Have not dug into unit
    yet to see if defrost board is bad, reversing relay is ok, as is changeover relay. Also
    reversing valve is ok.

    I was thinking of disconnecting all the defrost boards, and relays, and defrost sensor.
    Schematic says unit has a time, temperature defrost control.

    Was thinking of taking 24 volt wires from thermostat and direct wiring to relays
    to control contactor, and reversing valve.

    This unit is in central Texas where it rarely gets below 28 degrees, plus this unit is
    in a guest house in the country, so it is only used about 4 times a year. This is on
    a friends ranch, I stopped by to quickly look at for him.

    This guest house did have two Rheem heat pumps, but the second one developed
    a leak in the condenser, so I changed out that system for a new 1.5 ton unit with
    straight cool, and electric heat.

    Units are not used enough for the heat pump to pay for itself.

    Any one done this before?
    I have done this in a pinch. dont usually like to bypass boards, safety's ect longterm but in this scenario I dont see any reasons why it would matter. like you explained it's a guesthouse on a ranch gets used a handful of times a year.

    Sent from my SM-G975U using Tapatalk

  4. #3
    Join Date
    Jul 2007
    Location
    Virginia
    Posts
    11,714
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    Quote Originally Posted by edward301 View Post
    I have a 1986 Rheem 1.5 ton heat pump.

    I was thinking of disconnecting all the defrost boards, and relays, and defrost sensor.
    Schematic says unit has a time, temperature defrost control.

    Was thinking of taking 24 volt wires from thermostat and direct wiring to relays
    to control contactor, and reversing valve
    .
    Rheem units power the reversing valve in heat mode, so it should default to cooling when it is not energized with 24 volts.

    There should be no reason to wire in the reversing valve in your “wiring around the defrost control” project.

    You might want to remove the LPC and HPC (if installed) wires attached to the defrost control and wire them in series with the contactor.
    Instead of learning the tricks of the trade, learn the trade.

  5. Likes rollandsaxton liked this post.
  6. #4
    Join Date
    Mar 2016
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    74
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    Quote Originally Posted by rundawg View Post
    Rheem units power the reversing valve in heat mode, so it should default to cooling when it is not energized with 24 volts.

    There should be no reason to wire in the reversing valve in your “wiring around the defrost control” project.

    You might want to remove the LPC and HPC (if installed) wires attached to the defrost control and wire them in series with the contactor.
    great point

    Sent from my SM-G975U using Tapatalk

  7. #5
    Join Date
    Jan 2019
    Location
    Ct
    Posts
    11
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    If you're not going to use it for heat, why not just run it in emergency heat? Then only the backup heat should run.

  8. #6
    Join Date
    May 2004
    Location
    Austin, TX
    Posts
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    Thread Starter
    The high pressure control died years ago, wired around it. Want to use the heat pump since it
    still works. Thinking of wiring t stat directly to relays one for cool, and second for heat pump.
    The t stat can kick in elect heat if heat pump can not keep up, but not usually an issue here.

  9. #7
    Join Date
    Aug 2002
    Location
    Southold, NY
    Posts
    26,129
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    Quote Originally Posted by edward301 View Post
    The high pressure control died years ago, wired around it. Want to use the heat pump since it
    still works. Thinking of wiring t stat directly to relays one for cool, and second for heat pump.
    The t stat can kick in elect heat if heat pump can not keep up, but not usually an issue here.
    In Tx I hope another was installed!

  10. #8
    Join Date
    Mar 2018
    Location
    Kansas Flatlands
    Posts
    399
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    Quote Originally Posted by rundawg View Post
    Rheem units power the reversing valve in heat mode, so it should default to cooling when it is not energized with 24 volts.

    There should be no reason to wire in the reversing valve in your “wiring around the defrost control” project.

    You might want to remove the LPC and HPC (if installed) wires attached to the defrost control and wire them in series with the contactor.
    Or just pull the plug off the RV

  11. #9
    Join Date
    Jan 2004
    Location
    PA
    Posts
    78,378
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    You sure the RV isn't stuck in the heat position.
    Contractor locator map

    How-to-apply-for-Professional

    How many times must one fix something before it is fixed?

  12. #10
    Join Date
    Dec 2019
    Location
    Russellville, AL 35654
    Posts
    8
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    I wouldn't run heat pump without defrost control operating properly. If the reversing valve is ok you can disconnect a wire from it for it to be in cooling mode, then run y from tstat directly to contactor for cooling. For heat switch tstat to emergency.

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