Page 1 of 4 1234 LastLast
Results 1 to 13 of 44
  1. #1

    Confused Walk in freezer evap coil frosting up

    I am working on a walk in freezer. 404a. Evap. Coil was frosted over. I defrosted the coil, both sides. Tested defrost timer and elect heat, working ok. Turned system on. Suction pressure was 25-30. Suction line temp was moving from 0 to 9 deg. Air entering evap was 24. Air leaving 18 deg.
    As soon as I turned it on, the coil started frosting up. I let it run, but never wold drop below 20 deg.
    This system was working and has been for a long time.

  2. #2
    Join Date
    Apr 2003
    Posts
    139
    Is the lo side flu between 25-30, if so likely moisture in the system. Maby a low side leak and pulled some in on pump down (404 should set above a vac though), just a guess though. more info is always helpful....

  3. #3
    Join Date
    May 2010
    Posts
    1,291
    How frequently does the unit go into defrost a day? What are the defrost intervals? More info.....

  4. #4
    Join Date
    Jun 2012
    Posts
    41
    Superheat? Subcooling? Compressor RLA and Amp draw? Does your txv have an inlet strainer? Have you tested the power head? Does it sound like its starving?

    Off the bat it sounds like moisture in the system. 404a is a blend refrigerant as well. Leaks can throw off the percentages. Though it could be other things as well. Do you know if the orifice is sized correctly in the distributor? Does it ice at the TXV or at the Distributor? What's your defrost times? Is there a defrost terminate thermal disk? Is the customer leaving the door open? Are the door gaskets damaged?

    Get the base line readings of super heat, Subcooling and compressor amps and get back with us. Also you could bring up the door maybe left open by employees and then suggest a kill switch for the door. I'm a firm believer in door kill switches when it comes to walkin freezers.

  5. #5
    Door gasket is good. No one is opening the door to often at this time because school is on summer break. Subcooling is 5. It does have a defrost termination disk. Defrost timer is set for every six hours at 30min Intervals. The txv is frosting as well as evap. Frosting suction line up to cond but not frosting to compressor.

  6. #6
    Join Date
    Jun 2012
    Posts
    41
    With no Superheat, Subcooling or Amp draw readings I'm guessing here. If your unfamiliar with taking thoese readings check out YouTube or the web.

    If what I'm gathering from your original post is correct, your taking suction pressure/temperature at the Evap coil. These readings would make your Superheat 10F. This is if we're assuming your system is dry and has no leaks. If the Superheat is roughly 10F and the case temp is not yet at setpoint you may have too much refrigerant being metered through the TXV. I suggest tuning the TXV and metering less refrigerant.

    If your not a tech I would highly recommend hiring a pro to get it done. To attempt this repair without proper training can lead to bodily harm and lost of product. Both of which no one should have to afford and can be costly.

    If you are a tech then take Superheat at the Evap, Subcooling after the receiver, and Comoressor RLA on the common and also what is say on the data plate. If its 3phase t1 t2 t3 readings.
    Last edited by R&J-R; 06-19-2012 at 05:44 PM. Reason: Wrong refrigerant PT and Superheat

  7. #7
    Ok. Yes I gave superheat and subcooling readings already. I checked the amp draw but I did not write it down. I'll recheck it. Superheat was up and down because my suction line temp would go between 0 and 9 deg. Subcooling was 5.

  8. #8
    Join Date
    Jun 2012
    Posts
    41
    I do apologize for missing the subcooling. When I tune for superheat I like to see a 20-30f split while the walkin pulls down. Once you get close to desired set point, 0 or below, that's when I start going for tuning. I follow up later to see if any fine tuning is needed. Now if there's product in the walkin it'll take some time to reach setpoint before adjustments should be made.

    Have you left it on over night and does it still trend 22F? Or is the coil frosted to the point restricting air flow by then?

    The more I think about it, it sounds like to much liquid in the evap which frost quickly an lowers surface area enough that it impedes heat transfer out of the walkin

  9. #9
    I'll be checking it in the morning. I'll let you know. Thanks for your help

  10. #10
    Join Date
    Mar 2009
    Location
    Mid-Mo
    Posts
    3,594
    Are we talking frost or ice? There is a difference. Txv valve bulb insulated? How was it working and not now? Why were you over there? Pm?

  11. #11
    I called it frost. It wasn't hard ice. Bulb is insulated. Service call. Box was not dropping below 20 deg

  12. #12
    Join Date
    Jan 2010
    Posts
    6,091
    Is there a sight glass ? Did you check it ? 10* superheat for a freezer is to high if that's what you have. 4-6 is good with a 10* TD.

  13. #13
    Join Date
    Sep 2008
    Location
    Western PA
    Posts
    25,411
    Quote Originally Posted by VTP99 View Post
    Is there a sight glass ? Did you check it ? 10* superheat for a freezer is to high if that's what you have. 4-6 is good with a 10* TD.
    Check charge and defrost heaters.

Page 1 of 4 1234 LastLast

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
Comfortech Show Promo Image

Related Forums

Plumbing Talks | Contractor Magazine
Forums | Electrical Construction & Maintenance (EC&M) Magazine
Comfortech365 Virtual Event