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  1. #1
    At work the mobile modular office that is the sales office for the new construction homes, the heat pump wasn't cooling down the office. Since they couldn't bare the heat till tomorrow they had a service technician from our company take a look at the system.

    I know this guy so I was talking to him while he was checking the unit. On two of the three units he found a sheet of ice, I would say 1/4" thick at least. He pulled it off and through it down. He checked the superheat and the low pressure was at 96. High pressure at 300.

    He said that the system was overcharged. He said that they had the thermostat at 68 degrees and at night it remains at 72. He said while the low side pressure was at 96 degrees at night when it cools down the pressure in the low side drops much lower. He said the moisture in the air runs across the cold evaporator coil and begins icing over, until it becomes a sheet of ice. The sheet of ice was restricting the air flow.

    Is this right??


    He explained Dry Bulb, and Wet Bulb. So before I take what he said as fact.

    Dry Bulb: Outdoor Tempature

    Wet Bulb: He said that you take a the thermister and wrap it in a wet cloth and swing it in circles inside the R/A vent. He said this measures Humidity in the air.

    Sounds weird as hell, please no sarcasm, I'm here to learn from you gentlemen.

  2. #2
    Join Date
    Feb 2004
    Posts
    2,597
    damn, if the subs can't even do it right in the sales office,how do you think the permanent homes were done?

    oh well, good for business

  3. #3
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,875
    Being overcharged has nothing to do with a coil freezing.

    He is right that the suction pressure will drop as the outdoor ambient changes, but there is some thing else wrong that it froze.

    Thats one way of taking a wetbulb reading, I use a didgital sling.


    You should invest in some good books, or even some night courses.
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    How many times must one fix something before it is fixed?

  4. #4
    Join Date
    May 2005
    Posts
    428
    The ice is not the problem it is the result of the problem. airflow ,refrigerant charge ,restriction,plugged air filter wich falls under air flow.

  5. #5
    Join Date
    Jul 2002
    Location
    St Paul, Minnesota
    Posts
    3,468
    Once he adjusts the charge, get a superheat/subcool reading along with new set of pressure readings after the unit stabilizes. Also outside and inside temperature. That would be a start. You can find info on SH/SC here on this site. Wet bulb temp can be useful if it is a capillary tube coil. A wet cotton shoe lace in the return over a temp probe can be a good enough guess.

    Then a temp of the return air and supply air at the closest register or vent and someone might be able to have enough info to tell what is wrong. Clean filter in place? If not, do so, not too restrictive either. I will assume clean blower and evap coil, right?

  6. #6
    [I know this guy so I was talking to him while he was checking the unit. On two of the three units he found a sheet of ice, I would say 1/4" thick at least. He pulled it off and through it down. He checked the superheat and the low pressure was at 96. High pressure at 300.



    Is this a 410-A system? R-22 should not have any ice on the evaporator at these pressures. Also, what were the indoor and outdoor temperatures?



    [Edited by theredneckrev on 07-30-2005 at 08:22 AM]

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