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  1. #1
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    Mar 2019
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    Testing ac during low outside temperatures.

    I’m looking for some reasonable understanding and hard facts. I’ve got many years of experience working on just about everything and I spend a lot of time trying to learn everything I can. I’ve been licensed and certified in many things related to residential repair and automotive repair. For almost 10 years the job I have requires me to check to make sure that the HVAC in a currently occupied house gets cold. It runs for a very short time. Just long enough to get cold. That’s it. Nothing more. I do this 2 times a day 5 days a week. The only time I don’t try the AC is if it’s below freezing. My location is comparable to living in Louisville Kentucky. I hear all the time, you can’t run that AC if it’s below 60 degrees Fahrenheit outside because it will cause damage. In almost 10 years that’s never happened. Why

  2. #2
    Join Date
    Jul 2010
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    nebraska
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    Maybe lucky,maybe have caused some damage and didn't know it. Refrigerant will sit in a compressor and lift the oil out of it in cold weather. Your car will run a few minutes too with no oil but to declare the engine as undamaged by it simply because it ran isn't correct.

  3. #3
    Join Date
    Oct 2002
    Location
    Plano, TX
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    Refrigerant will condense in the coldest part of the system, typically outside if it is colder then inside the house. But some compressor have internal heaters that increase the temperaute above all other of the parts. Two issues with liquid refrigerant in compressor. One is that liquid will bust the valves as compressors only can compress vapor. Second, the liquid refrigerant and refrigerant oil will flash into vapor provide poor lubrication.

    What I see these days are heat pump compressors that do not have heaters that are expected to operate in sub zero temperatures. These compressors are scroll design and most AC condensing units also use these. Liquid will cause the "valve" assembly to lift and allow refrigerant to be bypassed.

    Scrolls still need lubrication, but volumes are less then reciprocal compressor. This may be why HP units do not fail in low ambient situation. Maybe, the short off cycle probably does not allow compressor to get colder then the indoor components. But I don't understand how a heat pump unit doesn't suffer damage when it is initailly started and with factory set up heat pump from flashing Refrigerant/oil mixture.

  4. #4
    Join Date
    Aug 2009
    Location
    Beatrice, NE
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    I'm sorry, I don't understand. What is the point of running a unit for 5-10 minutes twice a day 5 days a week? Why not every day if it is critical. Just producing "cold" really proves nothing when it is cold, there is no load on anything. Can you shed more light on what and why?

  5. #5
    Join Date
    Aug 2002
    Location
    Southold, NY
    Posts
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    The IOM will have specific instructions on how to check the charge. Most stat ambient must be above Xf!

  6. #6
    Join Date
    Jan 2004
    Location
    PA
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    Quote Originally Posted by BNME8EZ View Post
    I'm sorry, I don't understand. What is the point of running a unit for 5-10 minutes twice a day 5 days a week? Why not every day if it is critical.

    WAG. He's a home inspector, and he is seeing if the A/C blows cold in 2 houses a day, 5 days a week.

    Just producing "cold" really proves nothing when it is cold, there is no load on anything. Can you shed more light on what and why?
    Don't need a home inspector trying to do much more than see if the A/C operates.
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    How many times must one fix something before it is fixed?

  7. #7
    Join Date
    Jan 2004
    Location
    PA
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    Quote Originally Posted by MT3636 View Post
    I’m looking for some reasonable understanding and hard facts. I’ve got many years of experience working on just about everything and I spend a lot of time trying to learn everything I can. I’ve been licensed and certified in many things related to residential repair and automotive repair. For almost 10 years the job I have requires me to check to make sure that the HVAC in a currently occupied house gets cold. It runs for a very short time. Just long enough to get cold. That’s it. Nothing more. I do this 2 times a day 5 days a week. The only time I don’t try the AC is if it’s below freezing. My location is comparable to living in Louisville Kentucky. I hear all the time, you can’t run that AC if it’s below 60 degrees Fahrenheit outside because it will cause damage. In almost 10 years that’s never happened. Why
    How do you know it hasn't done harm. You don't see if the new home owner has to replace the system 2 or 3 years later.
    Contractor locator map

    How-to-apply-for-Professional

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

  8. #8
    Join Date
    Dec 2005
    Location
    Cincinnati, Oh
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    Location is comparable to Louisville?

    Yeah, that doesnt sound weird.

    Whats up with this new type of guest that gives us weird scenarios, instead of just outright asking?

    Its super weird.

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