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  1. #1
    Join Date
    Oct 2004
    Posts
    35
    came upon an airhandler furnace today model# GMPO75-3 i belive its a goodman not 100% sure. but my problem is that i can't get 24volts to contactor coil to the condenser.my first check was the thermostat,when calling for cooling thermostat is passing power there is 24volts at the secondary of the transformer,blower motor runs,this unit has a printed circuit board.terminal on board that connect to 24volts at contactor coil are r-and-g from those terminal on the board i get 24volts but when i connect wires nothing happens and yes i did ohm out wires no breakage.but when i connected wires from the contactor coil to secondary of transformer the condenser came on, is this board bad or what.

  2. #2
    Join Date
    Apr 2004
    Location
    Bartlett, IL
    Posts
    6,619
    Is it an air handler or is it a furnace??

  3. #3
    Join Date
    Oct 2005
    Location
    CT
    Posts
    4
    R and G Wires should be connected to Y and c. gis the fan circuit r is the hot side of transformer. What color wire is connected to y at t-stat if it is yellow find yellow wire at furnace connect to one wire going outside connect other wire to common of transformer "c" terminal. Bingo it runs.

  4. #4
    Originally posted by 2hot2coolme
    Is it an air handler or is it a furnace??
    You've never seen a GMP? Are you serious?

  5. #5
    Originally posted by grumpyyank
    R and G Wires should be connected to Y and c.
    Are you sure? If they are that would be a problem.

  6. #6
    Join Date
    Jan 2005
    Location
    yadkinville nc
    Posts
    530
    I think the board is fine. Check Y to common at furnace if you hve power there problem is not stat or wire from stat. If the outdoor unit won't run it usually has nothing to do with the control board. Seek professional help!!!!!!!!
    duct tape and cable ties will fix anything, if that don't work add a 90-340.

  7. #7
    Originally posted by j carter
    is this board bad or what.
    Board? No, not since the blower is running.

    Or what? Yes, you need to verify whether you have 24 volts at Y (which you don't). Beings you tested (y & c) by connecting directly to the transformer and it runs. The real question is why don't you have 24 volts on Y?

  8. #8
    Join Date
    May 2005
    Location
    Seabeck, WA
    Posts
    1,870
    Are there any high or low pressure switches? Is there power from Y to C at the condensing unit? Important questions for a service tech. . .
    Live for yourself and ask no one to live for you.

  9. #9
    Originally posted by inturmoil
    Are there any high or low pressure switches? Is there power from Y to C at the condensing unit? Important questions for a service tech. . .
    Re-read the original post. He says the condenser runs if he connects the Y & C to the secondary 24 volt power.

    Therefore, the pressure switches are out of the equation (even if they do exist). And there is no power at Y & C at condenser, because it's not running.

  10. #10
    Join Date
    Jan 2005
    Location
    yadkinville nc
    Posts
    530
    sounds like could be tsat or even a float switch or condensate pump float.
    duct tape and cable ties will fix anything, if that don't work add a 90-340.

  11. #11
    Join Date
    Sep 2002
    Posts
    4,970
    knock it off knuckleheads ...its a diy. As basic as that is he can ask his boss. Then his boss will question why he has him out there, Which he should

    [Edited by dec on 10-04-2005 at 12:58 AM]

  12. #12
    Originally posted by dec
    knock it off knuckleheads ...its a diy.
    Really?

    He starts out by saying "came upon an airhandler furnace today".

    In this post he posted "I am having a problem with a old whirlpool gas furance".

    In this post he posted "I recently serviced three marley cooling towers".

    In this post he posted "i am looking for a break down for a copland compressor the model # is erfi-0310-tad".

    In this post he posted "need understanding of the purpose of the chill water valve on a airhandler".

    In this post he posted "went to service a refrigerator today".

    In this post he posted "Today i came upon a water chiller model# M-50-rfc".

    Do you really think DIY'ers work on very many chillers? Or have this variety of equipment at his homes?

  13. #13
    Join Date
    Aug 2004
    Location
    North Richland Hills, Texas
    Posts
    14,914
    Originally posted by j carter
    terminal on board that connect to 24volts at contactor coil are r-and-g from those terminal on the board i get 24volts but when i connect wires nothing happens and yes i did ohm out wires no breakage.

    Connecting the 2 control wires from the outdoor unit to R and G on the control board won't do anything for you because there is not a good enough path to common through the G terminal. A meter will show that you have 24v, but you can't run anything with it because the path to common is through transistors. (Overly simplified, but it sounds like you probably wouldn't understand the real explanation)

    The 2 control wires from the outdoor unit whould connect to the thermostat wire that is connedted to Y at the thermostat, and to the 24v common from the control wire.
    There is no Y connection on the control board for the GMP furnaces. The common wire off the control board should be the blue one.

    Check to make sure you have 24v between Y and common when the thermostat is calling for cooling...

    If you are a DIY'er, please get a pro to look at the problem before you cause damage to yourself or your property.

    If you are a "pro", please get help from someone more qualified, and/or get some training in basic electrical troubleshooting.


    If more government is the answer, then it's a really stupid question.

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