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Thread: Added AC to existing heater. AC wont turn off automatic

  1. #1
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    Added AC to existing heater. AC wont turn off automatic

    I have a very strange issue with the AC we added to existing heater. If we run the AC to test and turn off in couple of minutes, it shuts off.
    But if on a hot day I keep the AC running for longer duration, it would not turn off when temperature is reached or even if I manually turn the sytem off.
    Then I did another test.
    When I run the heater, turns off as expected no problem.
    I did a test as below -
    1>Turn on AC to cool to 65 degrees
    2>It runs for 30 mins or so and keeps going even when temp reaches 65.
    3>I increase the threshold to 67, AC keeps running
    4>I then switched the system to Heat mode. Heater turns on, the compressor keeps running.
    5>In few minutes, I changed the mode to 'Off'. expecting the whole system to turn off.
    6>The heater turns off, but the AC keeps running.

    I have tried 3 different thermostats. The installation tech says there is nothing wrong in the system itself. And I am at a loss. Hopefully someone here has ideas I can try.

    Thanks so much!

  2. #2
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    Call your dealer back and have him see what's up. Should have a warranty.

  3. #3
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    Thread Starter
    Thanks BaldLoonie,
    The installer tech has come by few times but other than thinking that it is the thermostat to blame, he hasnt found anything yet.. which is where I am looking for ideas here.

    Thanks

  4. #4
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    Site rules prohibit giving technical advice to non-professionals. We won’t be able to help you.
    It seems your installation company is inadequate. You need to find a more skilled technician.
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  5. #5
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    Quote Originally Posted by mansat View Post
    Thanks BaldLoonie,
    The installer tech has come by few times but other than thinking that it is the thermostat to blame, he hasn’t found anything yet.. which is where I am looking for ideas here.

    Thanks
    Call the company again. And tell them you want a better tech sent out. One that has a better knowledge of control wiring.
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    How many times must one fix something before it is fixed?

  6. #6
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    Could be running in dehum overcool.

  7. #7
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    What's the thermostat?

  8. #8
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    Quote Originally Posted by BaldLoonie View Post
    What's the thermostat?
    The one MARK loved so much?

  9. #9
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    Thread Starter
    I have tested Nest, Honeywell and a Carrier thermostat. All have same results.

    Thanks!

  10. #10
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    It could be. How can I tell? I do not see any setting or configuration on thermostat to adjust this feature.

  11. #11
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    Thread Starter
    The tech now says that he control board is bad. And needs to be replaced! Another $$.

  12. #12
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    Keep guessing or find a different more qualified tech!

  13. #13
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    What board? A furnace's control board doesn't control the central A/C. Unless its an integral part of the furnace.

    Now would be a good time to post brand and model number of both the furnace and A/C.
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  14. #14
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    Thread Starter
    Interesting. Furnace and heater I have from before is Bryant. And AC is American Standard. Hopefully one of the two images from the board will help determine model.Name:  IMG_0045.jpg
Views: 176
Size:  680.8 KBName:  IMG_0042.jpg
Views: 169
Size:  502.2 KB

  15. #15
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    No, the same board is used in different models. The model number for the furnace will be inside the compartment that has the burners. The A/C model number will be on the outside unit.

    Also, a pic of the thermostat wires connected to the board can help.
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  16. #16
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    This seems like a classic symptom of a deranged Nest.
    I havent failed. Ive just found 10,000 ways that wont work. - Thomas Edison

    Its not whether you get knocked down, its whether you get up. - Vince Lombardi

    "In this house we obey the laws of thermodynamics" - Homer Simpson

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  17. Likes kdean1 liked this post.
  18. #17
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    Thread Starter
    Here are some more pics. Model number and wiring etc. Name:  IMG_0046.jpg
Views: 162
Size:  387.1 KBName:  IMG_0047.jpg
Views: 173
Size:  1.10 MBName:  IMG_0049.jpg
Views: 159
Size:  537.8 KBName:  IMG_0050.jpg
Views: 170
Size:  550.4 KB

  19. #18
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    That board doesn't control the A/C, so it isn't causing the A/C to not shut off.
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  20. #19
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    Do you have a handyman or home warranty working on this unit? Or is this a DIY repair?
    As this tech you speak of seems very much confused.
    I havent failed. Ive just found 10,000 ways that wont work. - Thomas Edison

    Its not whether you get knocked down, its whether you get up. - Vince Lombardi

    "In this house we obey the laws of thermodynamics" - Homer Simpson

    Local 486 Instructor & Service Technician

  21. #20
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    Thread Starter
    Thanks for the response. Do you have recommendation for next steps?

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