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  1. #1

    "FAN ON" switch causes AC to be on all the time

    Hello

    I had a neighbor install a new furnace in my house 2 years ago. He's been in the A/C business since at least the 1970s. The new furnace is one of the high efficiency furnaces that doesn't use the chimney (a Concord 90+ efficiency). Both the AC and furnace work properly, except for one problem. Ever since he installed the furnace, whenever I turn the switch on the thermostat to "Fan ON" (instead of AUTO), the Air Conditioner will also turn on and it will STAY ON, regardless of the temperature setting on the thermostat. In other words, I could leave the house for 2 hours after turning the fan switch to FAN ON, and the AC will run the entire time and the temp in the house will keep dropping regardless of any of the settings (and regardless of if the other switch is turned to heat or cool). My neighbor told me tonight that the green and yellow wires are switched and that he will be over Saturday to fix it. I just wanted to post this message here to see if he is correct...I don't want anything else to break if he is wrong. Any advice will be helpful. thanks. Todd, Omaha

  2. #2
    Join Date
    Nov 2000
    Location
    Eastern PA
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    68,944
    Doubtful that those wires are switched, but they are shorted somewhere in the system.
    Government is a disease...
    ...masquerading as its own cure…
    Ecclesiastes 10:2 NIV


  3. #3
    Join Date
    Jun 2011
    Location
    Wake Forest, NC
    Posts
    352
    Possibly a bad Tstat. Doubt that the wires are switched. Update us once you find the problem, Im curious to know what it was.
    It's not rocket-science...

    It's electromechanical thermodynamic engineering

  4. #4
    Join Date
    Sep 2002
    Location
    Northeast Ohio
    Posts
    4,842
    Have your neighbor (contractor) check the low voltage wiring.
    A good HVAC tech knows how, an educated HVAC tech knows why!

    DEM


  5. #5
    Join Date
    Aug 2008
    Location
    S. Grand Prairie
    Posts
    244
    Like they said...it doesn't sound like switched wires...you would have noticed other issues with the AC system since it's been 2 years. Let him check it and let us know what he finds...
    Originally Posted by ladyfire3374:

    "I used to wake up excited about the challenges of the day. Now the anticipation level is somewhere between a root canal and a colonoscopy."

  6. #6
    Join Date
    Nov 2000
    Location
    Eastern PA
    Posts
    68,944
    A question for the OP; have any optional devices been recently added to your HVAC system? Humidifier? Air cleaner? UV lights?
    Government is a disease...
    ...masquerading as its own cure…
    Ecclesiastes 10:2 NIV


  7. #7
    Join Date
    Feb 2010
    Location
    Ontario Canada
    Posts
    1,341
    Why is everyone saying it is not the wiring? Sounds like it could be the problem to me.
    Never give up; Never surrender!

  8. #8
    Join Date
    Jun 2011
    Location
    Wake Forest, NC
    Posts
    352
    If the wires were just switched when he puts the thermostat to "on" for the fan the condenser would come on, but not the blower fan. he said they both do.
    It's not rocket-science...

    It's electromechanical thermodynamic engineering

  9. #9
    Join Date
    Feb 2010
    Location
    Ontario Canada
    Posts
    1,341
    Quote Originally Posted by HVACTechNC View Post
    If the wires were just switched when he puts the thermostat to "on" for the fan the condenser would come on, but not the blower fan. he said they both do.
    The G back feeds through the stat to Y.
    Never give up; Never surrender!

  10. #10
    Join Date
    Jun 2011
    Location
    Wake Forest, NC
    Posts
    352
    Quote Originally Posted by trouble time View Post
    The G back feeds through the stat to Y.
    Whatch'a talkin' 'bout Willis?

    If that were the case then why wouldn't the voltage "back feed" through the stat even if it were wired properly and still bring on the condenser? The thermostat doesn't know or care which color wire is connected to which terminal and to what piece of equipment it goes to. I'm not following your logic on this one, please explain further.
    It's not rocket-science...

    It's electromechanical thermodynamic engineering

  11. #11
    Join Date
    Sep 2008
    Location
    Western PA
    Posts
    25,687
    Quote Originally Posted by trouble time View Post
    The G back feeds through the stat to Y.
    Please be careful not to get too technical in open forums.

    This is starting to border on DIY, guys.

  12. #12
    Join Date
    Jun 2011
    Location
    Wake Forest, NC
    Posts
    352
    I dont wanna break the rules, but I am curious about what he is talking about. I'm not following his logic, and if I am missing something I would like to learn.
    It's not rocket-science...

    It's electromechanical thermodynamic engineering

  13. #13
    Join Date
    Sep 2008
    Location
    Western PA
    Posts
    25,687
    Quote Originally Posted by HVACTechNC View Post
    I dont wanna break the rules, but I am curious about what he is talking about. I'm not following his logic, and if I am missing something I would like to learn.
    Maybe start a new thread in Pro's or have a private message conversation.


    I don't want to see the thread closed.

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