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  1. #1

    Confused HVAC unit that sticks in the ON position

    I'm in dire need of suggestions. We have an HVAC unit that is about 6 years old that is mounted on a roof in Arizona.

    Whenever it rains and irregardless of the temperature, the unit will either "stick" into the AC or heating mode and will not shut off at the thermostat.

    The inside temp will get down to 69 degrees or up to 86 when this is happening.

    We've had 8 technicians out for a total of about 20 hours. We've gone through two new thermostats and new wiring on the roof.

    There are no holes on the unit housing that would allow rain to come in.

    When the unit sticks into the AC or heating mode, I have to go outside and shut it off at the breaker until it dries out after a day or two.

    I realize that I just said "until it dries out", so I think that implies that water is getting into something, somewhere.

    But after 8 contractors and 20 hours, no one can find the cause.

    The contractors who have came out have all been under home warranty. I have to guess that the home warranty is not paying these contractors much money, although the previous two had put a serious effort into trying to find the problem.

    I spent a couple hours trying to research this on google this morning but I can't find anything similar.

    Any ideas? Thank you.

  2. #2
    Join Date
    Jul 2007
    Location
    Mount Airy, MD
    Posts
    7,281
    Thread relocated to AOP

  3. #3
    Join Date
    Jan 2004
    Location
    PA
    Posts
    68,803
    Next time it does it, call for service right a way. And don't turn it off. Easier to find the problem while its stuck on, then after you turn it off.

    Brand and model number might help us help you.
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    How-to-apply-for-Professional

    How many times must one fix something before it is fixed?

  4. #4
    Three of the contractors had access to the unit while it was stuck on and still couldn't find the problem. They left by simply disconnecting wires that each time, the next contractor had to re-attach. It's raining at the moment and I don't have a ladder to get on the roof, but I will get the brand and model number as soon as possible.

  5. #5
    Join Date
    Oct 2010
    Location
    Anderson, South Carolina, United States
    Posts
    7,780
    Home warranty company's don't use good techs, they use cheap techs. This sounds like a tough one though. Maybe faulty circuit board, relay, contractor or skinned tstat wire. If it is a part (control board) they should try and find why it went bad (motor over amount, water damage etc) and resolve the root problem so it doesn't happen again.

  6. #6
    Join Date
    Jul 2006
    Location
    Virginia
    Posts
    4,905
    if it only happens when it rains probably dont happen often as it harldy ever rains in Arizona its ussally best to not keep changing contractors on a problem like this as the next contractor dont know what the previous one did
    We really need change now

  7. #7
    Join Date
    Mar 2004
    Location
    Illinois
    Posts
    6,959
    Quote Originally Posted by jtrammel View Post
    Home warranty company's don't use good techs, they use cheap techs. This sounds like a tough one though. Maybe faulty circuit board, relay, contractor or skinned tstat wire. If it is a part (control board) they should try and find why it went bad (motor over amount, water damage etc) and resolve the root problem so it doesn't happen again.
    You may have just unintentionally offended several members... I think it's safe to say that there are quality techs that do home warranty work. I think the core problerm with home warranties is that they only want to pay the bare minimum to get the unit up and running and choose not to spend money on all recommended repairs.

    I have technicians who I would put up against anyone on this site who have performed home warranty work before I fired the home warranty companies.

  8. #8
    Join Date
    Sep 2003
    Posts
    1,677
    what type of heat, Natural Gas, Electric Strips or Heat pump?

    I see where you have to shut it off at the breaker to get it off....Does turning the thermostat to the off position while the unit is running all the time cause it to stop?

  9. #9
    Join Date
    Aug 2012
    Posts
    2,755
    Eight companies and not one could find the problem? That is a bit worrysome.
    My name is TooCoolforschool and I am a chronic over charger.

  10. #10
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,376
    Quote Originally Posted by AZ85261 View Post
    We've had 8 technicians out for a total of about 20 hours. We've gone through two new thermostats and new wiring on the roof.
    You mention "wiring on the roof" above. I must ask has the control wiring between the thermostat and the unit on the roof been looked at? How does the control wire (also called "thermostat wire", typically a brown or white cable with four or more wires of various colors) go into the house from the unit? Often this is through a roof jack, which is a device that seals electrical and plumbing penetrations through a roof. It could be when it rains, water is getting into the roof jack and shorting the control wiring between 24 volts and the heating or cooling wire, causing the unit to run non-stop.

    Problems with control wiring can be tough to spot and/or duplicate, but it can be done. Only other thing that would cause a rooftop unit to run when it shouldn't is a short within the unit itself, which will either be the unit's control wiring or control board. The tech should look for evidence of water entry into the unit's electrical component sections. Water usually leaves stains behind after it dries up.

    Has the house been reroofed lately?
    • Electricity makes refrigeration happen.
    • Refrigeration makes the HVAC psychrometric process happen.
    • HVAC pyschrometrics is what makes indoor human comfort happen...IF the ducts AND the building envelope cooperate.


    A building is NOT beautiful unless it is also comfortable.

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