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Thread: Frozen coils

  1. #1
    Join Date
    Jun 2001
    Location
    Northwest Indiana
    Posts
    1,302
    Its been awhile, but I'd like to submit these questions for the experts.
    R-22 split system, med temp application. Large warehouse cooler. Box temp to maintain 37F.
    Evaporator frozen, bottom 1/3 of coil.

    1 As the level of refrigerant decreases due to a leak, can it be said the increased pressure drop across the T.E.V. will in fact make the coil colder for a period of time and begin the process of coil icing?

    2 Once the coil is frosted over, the ice continues to build, getting thicker due to the lack of airflow across evaporator.

    3 One would expect the sight glass to flash or be half full. If the lower third of the coil is frozen have we actually decreased the size of the evaporator? If this is tue then we have decreased the total charge necessary to clear the glass.

    4 If the above statement is true, even though the system is low on refrigerant, the sight glass will or can be full due to the above condition. True or False?

    Untill enough regfrigerant has escaped, most techs will de ice the coil, write up the ticket and collect the cash. (none on this forum OfCourse) Only to be called out the next night cause the box is still warm.

    Thanks
    Bernie
    If you cant fix it right, try again.

  2. #2
    Originally posted by toptech
    Its been awhile, but I'd like to submit these questions for the experts.
    R-22 split system, med temp application. Large warehouse cooler. Box temp to maintain 37F.
    Evaporator frozen, bottom 1/3 of coil.

    4 If the above statement is true, even though the system is low on refrigerant, the sight glass will or can be full due to the above condition. True or False?

    Untill enough regfrigerant has escaped, most techs will de ice the coil, write up the ticket and collect the cash. (none on this forum OfCourse) Only to be called out the next night cause the box is still warm.

    Thanks
    Bernie
    #4 is wrong.


    As far as what most techs would do .... the way I understand it to work ... whenever a system is showing low on gas .... the first thing you must do is rule out icing.
    Cause until you have proven there is no ice anywhere on any coils .... you may become part of the problem rather than part of the cure.
    And ... unfortunately, that still goes on every day in this industry.

    Guys get in a hurry and just gas n' go. They think they're doing somebody ... somewhere ... a service. But their NOT!!!


    My boss just asked me this morning if I knew WHY a certain system on a market rack would begin to warm up if the rack was low on refrigerant. I said no. He explained that the circuit farthest away from the liquid header would usually be the very first to begin starving.

    hmmmm..... very interesting....



    Ice.... it should be cubed, or on a mountain or in your drink. But never anywhere else in refrigeration or airconditioning..... unless of course... you got an "ice builder" in a tank.

    Ice.... it's what to avoid.

  3. #3
    Join Date
    Feb 2003
    Posts
    1,166



    My boss just asked me this morning if I knew WHY a certain system on a market rack would begin to warm up if the rack was low on refrigerant. I said no. He explained that the circuit farthest away from the liquid header would usually be the very first to begin starving.
    hmmmm..... very interesting....

    Once you know which system you'll learn to bring 200 lbs gas with ya!




    Watts New, Ohm My, I been Electrically Commutated. Are U2.

  4. #4
    Join Date
    May 2004
    Posts
    11,967
    Butting in here…

    Rule of thumb, when a coil frosts it is either flooding or starving as long as the coil is clean with proper air flow. This is only part of your problem.

    R12 is correct.

    There is no place for ice in a cooler. If you partially block your coil with ice we will be in a whole new ballgame with explanations here.

    It will decrease the size of the working evaporator to the eye but flood the coil circuits with liquid refrigerant. Ice reduces needed system capacity which makes the condenser work longer and it ices up the evap quicker. When a system ices it causes the sight glass to show low charge.


    Another rule of thumb that I always use when with R-22 in a walk in cooler, big or small, there should always be a defrost time clock installed and set to 4 x 30 min compressor off –fans on. Pump down the unit and let the airflow defrost the coil for a while. I am sure there will be different opinions on this, but it has always worked for me.



    Start here……

    Melt the ice, all of it first. Repair any leak you find. Run the system and adjust your charge to ¾ liquid in the sight glass. Your superheat settings on the TXP are next and install a defrost timer. SPST

    When your box comes to temp and all settings are good then see if your sight glass is full. I am sure you will stop that dreaded ice monster.



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