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  1. #1

    Gas Furnace runs while in cool mode... NEED HELP

    Today at one of my service calls, the customer stated that the AC wasn't working properly. When I went in attic, the furnace was operating while in cool mode. This is a duel fuel system with gas as the primary heat and the heat pump for emergency heat. I took off the wires at the control board and jumped R and Y and O and the furnace did not come on.I took wires off at the thermostat and I jumped R,Y,O furnace did not come on, I jumped R,Y and the furnace did not come on. I went outside to see if I was getting 24v to outside unit while t-stat was in cool mode. I was getting 24v from Y to common but outside unit wasnt coming on. The pressure switch had been cut and wire nutted together. I then jumped y( t-stat wire) straight to contactor and the outside unit came on in cool mode and in heat pump mode . So apparently I have a bad defrost board. However, the gas furnace still continued to run. I don't think its the board because I took W off of the board and the outside unit ran and the furnace didn't come on.I cannot figure out why the furnace runs while in cool mode or EM heat mode. My co-workers think its the thermostat or a short somewhere in the t-stat wire. I'm not totally convinced its the thermostat. I'm missing something. Any advice or troubleshooting tip would be helpful! Thanks

  2. #2
    Join Date
    Oct 2010
    Location
    Anderson, South Carolina, United States
    Posts
    6,742
    Why is the heat pump the emergency and the gas primary, sounds backwards to me. Sounds like something's messed up in the low volt wiring scheme

  3. #3
    Yea I plan on changing the primary heat to heat pump when I go back Thursday to replace defrost board.

  4. #4
    Join Date
    Jul 2009
    Location
    ohio
    Posts
    100
    when i get mess's like this i just gut the old wiring and start over the way it should be... most often its faster then figuring out what the last guy did and when you leave you'll know its right..... HO loves to hear " this is gonna be awhile ".
    read,learn,grow.....repeat.

  5. #5
    Ok thanks samejj.

  6. #6
    Join Date
    Nov 2011
    Location
    USA
    Posts
    377
    Quote Originally Posted by Rookie2012 View Post
    This is a duel fuel system with gas as the primary heat and the heat pump for emergency heat.
    I'm having some difficulty understanding how that was accomplished in the first place, with a typical heat pump stat and "dual fuel" accessory control.

  7. #7
    Join Date
    Dec 2007
    Posts
    4,690
    what thermostat?

    how is it programmed?

    how is dual fuel controlled?

    why is pressure switch out of the loop?
    The Food Stamp Program, administered by the U.S. Department of Agriculture, is proud to be distributing the greatest amount of free meals and stamps EVER.
    Meanwhile, the National Park Service, administered by the U.S. Department of the Interior, asks us to "Please Do Not Feed the Animals". Their stated reason for this policy "... the animals become dependent on handouts and will not learn to take care of themselves."
    from an excerpt by Paul Jacob in Sun City, AZ

  8. #8
    Join Date
    Jan 2007
    Location
    Indiana
    Posts
    66
    If it was the high pressure switch disconnected, in heat mode wouldn't the head pressure get really high if you are running the gas furnace and heat pump lol?

  9. #9
    Join Date
    Nov 2009
    Location
    Kansas City
    Posts
    124
    Just when you think you have seen it all, you run into something else. I've never seen the gas furnace primary with heat pump being the EH.
    I did have that problem one time and what was happening I found the W touching Y inside the wall where they shot a nail through the wire when it was installed 15 yrs prior. I couldn't believe it ran for 15 yrs before finally showing

  10. #10
    Join Date
    Feb 2012
    Location
    Pacific Northwest
    Posts
    96
    Quote Originally Posted by samejj View Post
    when i get mess's like this i just gut the old wiring and start over the way it should be... most often its faster then figuring out what the last guy did and when you leave you'll know its right..... HO loves to hear " this is gonna be awhile ".
    This is EXACTLY what I do every time.

    (The bad part is that 9 out of 10 times it was my co-worker that wired it all screwed up to begin with)

  11. #11
    Join Date
    May 2011
    Location
    Central Texas
    Posts
    84
    I'd be willing to bet that the W wire going from T-stat to furnace is shorted. I had a service call a few weeks ago on a Trane furnace were that was the culprit. Good luck.

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