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  1. #1
    Join Date
    Nov 2005
    Posts
    12
    I need some advice on a walk-in cooler.

    The evap coil has a new TxV, no defrost element, and the fan is wired directly to a light switch (always on). The rooftop condensing unit (tecumseh w/ reciever, R-12, 115V, 13.2 RLA) is controled by an in-line temp. sensor (on/off - johnson controls) hanging in the cabinet, and a grasslin defrost timer (on roof).

    The high side was 110psi w/ a subcool of about 8*. Superheat is around 35*. There's almost a 20* rise in refrigerant temp from coil input (~20*) to coil output (~40*). The air temp difference over the evap coil is only 3-4 degrees, which is a problem. I've checked for temp. drop/rises on both lines and there don't seem to be any restrictions. I have been told that the entire coil freezes up, but I've never actually seen it that way. What's worse, the walk-in has reportedly never 'really' been cool enough.

    Here's the deal - this equipment (along with alot of other antiques) is in my family's place of business, and after constant complaints about the HVACR contractor they use, I decided to take a look around (commercial refrigeration isn't my thing). Long story short, he's not allowed back on the premises and I have no faith in anything he's done, including the new TxV. I also can't trust whoever worked on it when it 'belonged' to the last tenant, as someone 'resized' the cooler with a HOLLOW wall (I fixed that few months ago after someone removed a picture from the wall and found a cold, wet, moldy, nasty surprise).

    So here's the $10,000 question: from what I've described, is it possible that the TxV is the wrong size or way out of adjustment? Could it be that the entire system is completely undersized? I couldn't find any plate data on the evap coil, but here's some pics of the setup:

    http://66.221.7.56/Pictures/PICT0866.JPG
    http://66.221.7.56/Pictures/PICT0867.JPG
    http://66.221.7.56/Pictures/PICT0868.JPG
    http://66.221.7.56/Pictures/PICT0869.JPG

    Any help/insight would be greatly appreciated.

  2. #2
    Join Date
    Jun 2001
    Location
    San Diego, CA
    Posts
    1,149
    Replace the whole thing and be done with it. Seeing as it's R12 - this has probably been recommended a dozen times by now so just do it and get on with it.

  3. #3
    Join Date
    Jul 2001
    Location
    Gold Coast of Connecticut
    Posts
    4,578
    I would set the defrost timer to defrost 30-45 mins every 4 hours, set t-stat to 35-40. By the frost pattern the txv looks to be feeding well, but you should check the adjustment. I would clean the coil very well, br sure the sightglass is clear and you have low ambient controlls on the outdoor unit.

    The single fan coils are usally only 4000-6500 btus when clean and with the correct fan blade and motor?

    We need the compressor #s and txv #s.


    [Edited by Freezeking2000 on 11-26-2005 at 05:38 PM]
    Aire Serv of SW Connecticut- Gas heat, dual fuel and central a/c systems installed and serviced

  4. #4
    Join Date
    Jul 2005
    Location
    Southern California
    Posts
    585
    could be undersized after someone 'resized' the box. what is the size of the box and how many doors? glass doors?

  5. #5
    Join Date
    Nov 2005
    Posts
    12
    The txv is labeled "82" with a "B" underneath it.

    The compressor/condensing unit is an AJA4492AXA.

    The box was actually resized a foot smaller along one wall. The door/walls are moisture resisant plywood, plastic sheeting, styrofoam & insualtion. It measures 10'x5'x7'.

    Thanks for the recommendations. As far as checking the txv settings, what's the best way to do that?


  6. #6
    Join Date
    Nov 2005
    Posts
    575
    That 4492 is a 3/4 high temp unit, with wood construction and any glass doors at all this is sooooo under sized.


  7. #7
    Join Date
    May 2000
    Location
    Monmouth Junction-NJ-USA
    Posts
    6,002
    Keeprite says if the box is 5x10x7 with 1 entry door, 3" Styrofoam (assuming it is 2x4) construction, concrete floor and 3" styrofoam ceiling the load is 5100 btuh. With r-134 and a 30 deg evap it equates to 1/2 hp air cooled condensing unit.

    [Edited by rayr on 11-27-2005 at 08:56 AM]
    If you really know how it works, you have an execellent chance of fixin' er up!

    Tomorrow is promised to no one...

  8. #8
    Join Date
    Jul 2005
    Location
    FLORIDA
    Posts
    1,163
    it looks like the evap is starving
    does it have a sight glass
    what is the suction presure's
    how long does it take to get looking like that{ half way through its cycle }

    assuming it once was a working unit and that the box has not lost its integrity you should be able to get this thing running fairly easy with a recharge of 12 or a retro fit of mp 39 or 134a

    once you think you've seen it all
    (THINK AGAIN)
    I would rather work for free than be look upon as a thief!!!!!

  9. #9
    Join Date
    Jul 2001
    Location
    Gold Coast of Connecticut
    Posts
    4,578
    Have you checked the LL filter for a restriction? is the sight glass clear? What temperature is the box with the frost on the coil?(in pic) Is the coil clean?

    What pressures is the unit running? Is the condenser clean?

    Normally you check a txv for proper operation using superheat? What are the suction line temps?
    Aire Serv of SW Connecticut- Gas heat, dual fuel and central a/c systems installed and serviced

  10. #10
    Join Date
    Nov 2005
    Posts
    12
    The unit does not have a sight glass.

    Suction pressure was 13psi.

    The picture was mainly to show the setup (taken during defrost). The lines from the txv to the coil are usually coated in ice about 1/2" thick. Coil temp (checked at the tubing bends) is about 20* where the refrigerant goes in, dropping to about 30* at the bottom, and rising up to about 38* to 40* at the sensing bulb.

    The evap coils could use a cleaning, but you can still see through them just fine - it's mainly just a little surface gunk in the back. The condenser is very clean.

    Also, this is probably a silly question, but should the fan be pulling air in or pushing it out? It was recently replaced, and seems to be the only one in the place that pushes instead of pulls...



    Just got off the phone, seems to be cooling to 40* without freezing up...for now.

    Thanks again for the help - this probably won't be the last time I need it :P

  11. #11
    Join Date
    Jul 2001
    Location
    Gold Coast of Connecticut
    Posts
    4,578
    You MUST have a sight glass or at least do a sub cooling. This thing may just need gas......good luck!

    Why did you not install a sight glass?...........at least!
    Aire Serv of SW Connecticut- Gas heat, dual fuel and central a/c systems installed and serviced

  12. #12
    Join Date
    Nov 2005
    Posts
    12
    Like I said, I 'inherited' this mess when I ran off the contractor - I do controls, I'm just now learning HVACR (I am E.P.A. certified). After going through most of the equipment on the roof, I couldn't find a single sight glass installed on any equipment, and there are a few condensing units that don't even have filter/dryers. There are rusted service valves with no caps, 'open air disconnects' at EVERY device, and most of them aren't even covered from the elements. To top it off, I found 2 empty 30lb bottles of hot shot on the roof - but I have yet to see a refrigerant label on ANY piece of equipment.

    Anyway, it's my mess now, and I'm working on fixing everything legally and correctly.

  13. #13
    Join Date
    Apr 2004
    Posts
    395

    Unhappy

    Why in hell are you trying to fix a hacked to hell P.O.S. like that? That thing is a call back waiting to happen plus unsafe with the way its wired up. Working for family is hard. I have been there you dont want to be the bad guy and say "sorry it cant be fixed" but you are going to spend more in the long run in time parts and all you going to end up with is an undersized box that was hacked to hell.
    I am not a refrigeration guy but you got to know what your subcooling to know whats going on in the bad boy.
    Tin Knockers BANG for a living

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