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  1. #1
    Join Date
    May 2005
    Location
    Indianapolis, IN
    Posts
    255

    reversing valve power

    where does the call for the reversing valve come from during defrost? I have a lennox HP that is putting out 4~5 volts during a call for HEAT. It wont go into defrost when forced from the defrost pins (defrost stat jumpered closed) but will defrost if i jumper R-O on the defrost board and pull the fan lead. This tells me the board is bad but wondering why I'm getting the voltage on the reversing valve wire. Any thoughts?

  2. #2
    Join Date
    Dec 2005
    Posts
    1,923
    Quote Originally Posted by chrashley View Post
    where does the call for the reversing valve come from during defrost? I have a lennox HP that is putting out 4~5 volts during a call for HEAT. It wont go into defrost when forced from the defrost pins (defrost stat jumpered closed) but will defrost if i jumper R-O on the defrost board and pull the fan lead. This tells me the board is bad but wondering why I'm getting the voltage on the reversing valve wire. Any thoughts?
    It would help a lot if you give us AT LEAST model of the unit. We don't care the color of the unit or the pad it sits on.
    Just model baby.

  3. #3
    Join Date
    Oct 2011
    Location
    between here and over there
    Posts
    453
    On some Lennox residential heat pumps there is a out door temp sensor or coil sensor (I cant remember which and I don't have a wire diagram handy) but you have to jump it out on the defrost board then jump the test pins. I have also seen that there are a few different types of defrost boards that lennox uses, they all work the same but the design of them are different. hope this was somewhat helpful. model and Serial numbers would help a great deal.
    ®

  4. #4
    Join Date
    May 2005
    Location
    Indianapolis, IN
    Posts
    255
    m-12hpb24-9p
    s-5803g91461

    thanks for the replies so far

  5. #5
    Join Date
    Feb 2009
    Location
    Tallahassee, FL
    Posts
    6,051
    All the boards ive messed with had one PCB relay that energized w2 and o.

    24v usually comes from red wire.

  6. #6
    Join Date
    Jun 2009
    Location
    Upstate SC
    Posts
    1,439
    Quote Originally Posted by SBKold View Post
    All the boards ive messed with had one PCB relay that energized w2 and o.

    24v usually comes from red wire.
    X2

    If the RV is energized in heating then 24v comes from stat

    Sent from my ERIS using Tapatalk 2

  7. #7
    Join Date
    Jun 2009
    Location
    Upstate SC
    Posts
    1,439
    Quote Originally Posted by chrashley View Post
    where does the call for the reversing valve come from during defrost? I have a lennox HP that is putting out 4~5 volts during a call for HEAT. It wont go into defrost when forced from the defrost pins (defrost stat jumpered closed) but will defrost if i jumper R-O on the defrost board and pull the fan lead. This tells me the board is bad but wondering why I'm getting the voltage on the reversing valve wire. Any thoughts?
    If you jump r to o and pull the fan lead that's not defrost mode that's AC mode without a condensor fan. 4-5 volts may be a bleed through. Is that with the coil hooked up?

    Some units have an ambient sensor that wont allow defrost above a certain temp.

    Sent from my ERIS using Tapatalk 2

  8. #8
    Join Date
    May 2005
    Location
    Indianapolis, IN
    Posts
    255
    Quote Originally Posted by jdblack View Post
    X2

    If the RV is energized in heating then 24v comes from stat

    Sent from my ERIS using Tapatalk 2
    this is what i thought. i think i just got thrown a little because of the little bit of voltage on the O wire while in heat. Prolly two separate issues. I'll change the board, ad then address the voltage issue.

  9. #9
    Join Date
    May 2005
    Location
    Indianapolis, IN
    Posts
    255
    Quote Originally Posted by jdblack View Post
    If you jump r to o and pull the fan lead that's not defrost mode that's AC mode without a condensor fan. 4-5 volts may be a bleed through. Is that with the coil hooked up?

    Some units have an ambient sensor that wont allow defrost above a certain temp.

    Sent from my ERIS using Tapatalk 2
    Yes, I understand that. I was just trying to say that its not a refrigerant issue. sorry to confuse. Its cold here in Indy, cold enough to need defrost for sure.

  10. #10
    Join Date
    Dec 2005
    Posts
    1,923
    Quote Originally Posted by chrashley View Post
    where does the call for the reversing valve come from during defrost? I have a lennox HP that is putting out 4~5 volts during a call for HEAT. It wont go into defrost when forced from the defrost pins (defrost stat jumpered closed) but will defrost if i jumper R-O on the defrost board and pull the fan lead. This tells me the board is bad but wondering why I'm getting the voltage on the reversing valve wire. Any thoughts?
    Now we got model.
    This unit has a non-intelligent demand defrost board, which means: defrost stat and time.

    Check your 24 volt Common and 24 volts hot AT THE BOARD. It needs it to function.
    If you have them AT THE board and did what you did, then replace the board.

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