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  1. #1
    Join Date
    Dec 2012
    Location
    Naperville, IL
    Posts
    1

    HVAC Student question about frozen evaporators

    In class last night we were charging a very under charged system. While doing so, with the help of an aid instructor, the suction line was freezing up for quite some time and suddenly the unit kept short cycling and high side pressure kept surging up, then compressor would shut down, then once the pressure dropped it would cycle on again. I never got an answer to why this might be happening, however I suspect that the evaporator might have froze up, or that the metering device froze? Any input would be greatly appreciated.

  2. #2
    Join Date
    Jun 2003
    Location
    Chicago, IL
    Posts
    4,524
    That system had two problems. Low load and a severe overcharge.

    The low load was causing the freezing and the overcharge was causing over pressurization which was why your high side pressure would surge when the compressor started. Then It would shut off on the overload or high pressure switch if it has one.

    Did you measure superheat and subcooling?

  3. #3
    Join Date
    Mar 2009
    Location
    Mid-Mo
    Posts
    3,596
    Sure sounds like it was cycling on one of the safeties. What were the pressures? Also any superheat/sub cool numbers would be helpful. Also maybe what the equipment was.

    If it was the low pressure switch and you were indeed severely low on charge that would explain a lot. Just because you are adding and your gauges read 100 psi (making that up) doesn't mean that's what your pressure switch is really seeing.

  4. #4
    Join Date
    Aug 2012
    Posts
    2,720
    The big question is did it get solved? If not why not?

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