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  1. #1
    Join Date
    Jan 2008
    Location
    Fuquay-Varina, NC
    Posts
    22

    Unit running without thermostat

    I am working on a unit and installed a honeywell focuspro 5000 thermostat. I have it operating by batteries. I can flip the disconnect on outside, and the unit will run even if the thermostat is switched to off. I have Y and C going to the contactor coil, and it is getting voltage even with the thermostat switched to off. Could the thermostat be bad? All the wiring in the airhandler and the outdoor unit appear to be wired right by the schematic. Thanks!

  2. #2
    Join Date
    Apr 2004
    Location
    Charlotte, NC
    Posts
    648
    By the wiring, it shows the C terminal as optional when choosing not to use batteries, which means the thermostat is using it as a common. I also has a standard 5 minute wait time when the unit is first started. See if this is the case.
    "Fighting Ignorance since 1973 (It’s taking longer than we thought)." The Straight Dope.

  3. #3
    Join Date
    Jan 2008
    Location
    Fuquay-Varina, NC
    Posts
    22
    I do have it wired to run off of unit power as well. Even with the thermostat off, I read 24 volts across the contactor coil

  4. #4
    Join Date
    Mar 2007
    Location
    media,pa
    Posts
    80
    contacts welded in the t-sta? short in the wiring?

  5. #5
    Join Date
    Jan 2004
    Location
    PA
    Posts
    68,793
    Reread the wiring diagrams.
    or is this why you changed the thermostat in the first place.
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  6. #6
    Join Date
    Jan 2004
    Location
    PA
    Posts
    68,793
    Reread the wiring diagrams.
    or is this why you changed the thermostat in the first place.
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  7. #7
    Join Date
    Jan 2008
    Location
    Fuquay-Varina, NC
    Posts
    22
    I changed the thermostat becaue it had an 1800's style mercury bulb! It worked fine before I changed the thermostat, atleast that is what I was told.

  8. #8
    Join Date
    Mar 2007
    Location
    media,pa
    Posts
    80
    don't allways believe what you are told.with the t-stat off do you have 24 volt's at the furnace or a/h going to the cond.

  9. #9
    Join Date
    Jan 2004
    Location
    PA
    Posts
    68,793
    Since your still in school. I hope your doing this for family, or a friend.

    Read the wiring diagram. And then reread the wiring diagram.
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  10. #10
    Join Date
    Jan 2008
    Location
    Fuquay-Varina, NC
    Posts
    22
    I have 24 Volts across the contactor outside. That was the only voltage check I did today!

  11. #11
    Join Date
    Jan 2008
    Location
    Fuquay-Varina, NC
    Posts
    22
    I am auctually doing this for a friend. If I can't figure it out, I will just have to put the old t-stat back on.

  12. #12
    Join Date
    Jan 2004
    Location
    PA
    Posts
    68,793
    Get your meter out, and trace your wires.
    At the moment, I vote for a miswired stat.
    But friends aren't always honest about how well something worked, when they ask if you'll do something like this.
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  13. #13
    Join Date
    Jan 2008
    Location
    Fuquay-Varina, NC
    Posts
    22
    I found out today that the unit outside was not wired right. It is a Lennox outdoor unit and an American Standard air handler. Both were wired by the schematic, but they both used different wire colors, so it was miswired outside. It runs great now, and the t-stat was fine!

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