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Thread: frosting evap.

  1. #1
    Hi there,

    I've got a problem with an evap coil. Expansion valve went bad, took out the compressor. Replaced both, installed new drier, now the coil will frost up in a matter of 12 hours. This is a walk in cooler, roof top self contained unit, R-22. Head pressure 225, suction pressure 50 lbs. box temp 43 degrees. What things should i check out?


  2. #2
    Join Date
    Jul 2001
    Gold Coast of Connecticut
    It should have a sefrost timer shutting it off every 6 hours for 30 mins for starters. Need to check super-heat ect!

  3. #3


    had this problem two months ago

    Check out the t-stat, could be sticking on causing the coil to freeze, therefore when the coil ices up the temp in the box also goes up due to the blocked coil

    one other question, does ice form on the coil right away or does it happen overnight

  4. #4
    I know this is a dumb statement but, it has worked for two years without a defrost timer. Why now?

  5. #5
    Join Date
    Sep 2002
    South Dakota

    If it did not or does not have a defrost timer then it was set up as an "Off Cycle Defrost" system. That is accomplished by the cut-in and cut-out settings on the LPC if it uses one for temperature control. If it uses a thermostat for temperature control then it should be a "constant cut-in" temperature control or an adjustable cut-in and cut-out thermostat attached to the coil with the cut-in setting above freezing.

    Has someone messed with the settings or replaced the thermostat with the wrong one?

  6. #6
    Has the product load changed since the last two years?

    Is there now more humidity being introduced to the walk in box?

    Is the TX mounted properly?
    What is your evaporator superheat?

    Is your condensor spotless clean? Did you recently wash it yourself?
    This is critical!!!

    Do you know this system personally? Can you verify this system, verbatum, has worked correctly for the last two years?

    I dont listen to the customer when they tell me stories like that.
    I dig in. Somethig has to have been changed. It just has to have been.

    I mean ... hey ... this is NOT Rocket Science!
    And this is NOT Supermarket Refrigeration either! So it has to be something pretty darned simple.

    Download the compressor curve from the manufacturer's site and then you'll be able to compare what the temperatures and pressures are at the given times. And have on hand the proper amp draw this unit should be drawing when it's operating at those pressures!

    You could have a weak unit. Even fresh from factory.

    Start out there.

    Then come on back here and we'll help ya some more.

  7. #7
    Join Date
    Jul 2001
    Gold Coast of Connecticut
    I would think for some reason your evaporator temp has gotten lower due to starved evap, plugged evap(dirt) or short on gas!

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