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Thread: Low voltage

  1. #1

    Low voltage

    I blew a 5 amp fuse on 24 volt transformer in air handler on trane heat pump, installing new thermostat. That caused a low voltage problem at the solenoid on the reverse valve. I have 27 volts at terminals to solenoid but it drops off the chart if I connect the solenoid. Solenoid works fine with proper voltage. Reverse valve fine with test magnet. I was thinking maybe I damaged the transformer in the air handler. It is showing 27 volts with 240 volt input under load. The unit was working fine before. I put the old thermostat back in and the unit runs fine in AC mode as long as I use a test magnet to hold the reverse valve in that mode. Low voltage wires test OK! Anyone run across something like this?

  2. #2
    Join Date
    Dec 2002
    Location
    SouthEast NC ICW & Piedmont Foothills
    Posts
    7,635
    1-what brand of t-stat did you attempt to use as replacement?

    2- me thinks you didn't wire/configure t-stat correctly

    3- hard to tell from here................but almost anything is possible
    It`s better to be silent and thought the fool; than speak and remove all doubt.

  3. #3

    Low voltage

    Yes! You are right that I wired the new thermostat up wrong. It is a Honeywell Pro 5000 and I should have kicked myself for not looking at the new wiring diagram first. I have checked all of my low voltage wiring for continuity and found no faults. The transformer checked ok but I tried a new one just to be sure. I reinstalled the new thermostat and the unit cycles fine in cool mode as long as I use a permeant magnet to hold the reverse valve in cool mode. I have not had a chance to see if the new thermostat has energized the solenoid on the reverse valve. My thinking is that the old thermostat may not have been sending a cooling mode signal. I will know tomorrow when I get a chance to check the current flow to the solenoid. I do not think that the thermostat was the problem! I have checked the wiring, the transformer, the solenoid,and the thermostat. I wondering if the logic board that controls the reverse valve could have been damaged when I screwed up the wiring and blew the fuse? Replacing that board is the last thing I can think of if the new stat does not fix it. Need some expert advise!! Thanks!!

  4. #4
    Join Date
    Dec 2002
    Location
    SouthEast NC ICW & Piedmont Foothills
    Posts
    7,635
    I foresee the fuse blowing again,

    do yourself a favor and call a service company to do it correctly
    It`s better to be silent and thought the fool; than speak and remove all doubt.

  5. #5
    Join Date
    May 2009
    Location
    oklahoma
    Posts
    298
    good grief read install manual for stat. unplug furnace when working on things. what brand is equipment? you will find your answer instructions. and get rid of magnet. or ya call someone that knows no shame. your board is fine...for now

  6. #6
    Join Date
    Dec 2002
    Location
    SouthEast NC ICW & Piedmont Foothills
    Posts
    7,635
    it's a trane heat pump........does that give you a clue of what he is doing wrong, seen it before.
    It`s better to be silent and thought the fool; than speak and remove all doubt.

  7. #7
    Join Date
    Jul 2006
    Location
    Virginia
    Posts
    4,808
    The trane reversing valve is energized in cool mode .in the tstat set up did you set it up for a 2 heat i cool heatpump and the valve setup should be on o

  8. #8
    Join Date
    Sep 2008
    Location
    Western PA
    Posts
    25,862

  9. #9
    Join Date
    Dec 2002
    Location
    SouthEast NC ICW & Piedmont Foothills
    Posts
    7,635
    CAT MAN-----------------------you didn't have to.......did you
    It`s better to be silent and thought the fool; than speak and remove all doubt.

  10. #10

    Low voltage

    As it turns out the thermostat was faulty. It energized the solenoid but not enough for current to flow when a load was placed on it.

    Thanks for the input!

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