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Thread: Walk in help

  1. #1
    Join Date
    Aug 2004
    Location
    Kentucky, Michigan, Ohio, Arizona, Colorado, Nevada, and Califormia
    Posts
    318

    Walk in help

    Forgive me, I'm an HVAC tech not HVAC-R and this is probably an obvious problem to most of you. I thought it would be fun to install the evap and condenser on a walk in cooler. Our company doesn't do low temp so I did it on the side. The box is 10 by 8 by 8. The unit I installed was :
    Bohn ADT120AK
    D07A10852
    Evap

    Russell RLH151H22D
    W06A32645504001
    Cond.

    I followed all directions, LL solenoid, 6 hour vacuum, nitrogen thru brazing and for pressure test, insulated drain line w/trap, etc. The problem is the bottom half of the evap frosts 1/2" thick over night. I have 3 defrost times of 10pm 4am and 2pm @40 minutes each. The customer wants the box as cold as he can get it...I set it @ 36 and locked the stat. 2 degree differential.
    I was wondering if the defrost length was too much, allowing the box to warm up too much and then causing extended run time-IE the frosting. The customer wants me to add another defrost pin and increase the defrost length to 60 minutes. Also on the Cond. tag it says "evap temp rating 0-30F" does this mean the condenser is for a freezer and not a cooler ? With the box @ 38 I had 45 suction, 225 head, ODT of 75, clear sight glass, no pattern frosting and the TXV was maintaining acceptable superheat. Sorry for the long post. Thanks.
    "Surprised ?! If I woke up tomorrow with my head sewn to the carpet, I wouldn't be more surprised."
    Clark Griswold

  2. #2
    Join Date
    Aug 2004
    Location
    Kentucky, Michigan, Ohio, Arizona, Colorado, Nevada, and Califormia
    Posts
    318
    All equipment was supplied by the store owner and even though it was a "side" job, I am my companies lead tech and made the powers that be, aware of what I was doing.
    "Surprised ?! If I woke up tomorrow with my head sewn to the carpet, I wouldn't be more surprised."
    Clark Griswold

  3. #3
    Join Date
    Jul 2000
    Location
    Guayaquil EC
    Posts
    10,331
    Did you install the nozzle in the evaporator distributor? A missing or incorrect nozzle size is a common cause for uneven refrigerant feed that can result in icing like you describe.

  4. #4
    Join Date
    Aug 2004
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    Kentucky, Michigan, Ohio, Arizona, Colorado, Nevada, and Califormia
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    Boy am I gonna sound dumb... Nozzle ? Is this similar to a piston ? The metering device is a TXV. The frost usually takes about 8 minutes to thaw and it is only present when they open the store @ 6am. Would this have something to do with the lack of load ? They are closed 10pm to 6am.
    "Surprised ?! If I woke up tomorrow with my head sewn to the carpet, I wouldn't be more surprised."
    Clark Griswold

  5. #5
    Join Date
    Aug 2004
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    Kentucky, Michigan, Ohio, Arizona, Colorado, Nevada, and Califormia
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    During other times, the box will achieve desired temps, even down to 32.
    "Surprised ?! If I woke up tomorrow with my head sewn to the carpet, I wouldn't be more surprised."
    Clark Griswold

  6. #6
    Join Date
    Jul 2000
    Location
    Guayaquil EC
    Posts
    10,331
    Quote Originally Posted by lra View Post
    Boy am I gonna sound dumb... Nozzle ? Is this similar to a piston ? The metering device is a TXV. The frost usually takes about 8 minutes to thaw and it is only present when they open the store @ 6am. Would this have something to do with the lack of load ? They are closed 10pm to 6am.
    There's no such thing as a dumb question, only dumb answers....so I'll try to appear brilliant.

    Look in the Heatcraft I&O manual that came with the evaporator and on p.7 you'll find the section dealing with the distributor nozzle. There are usually two nozzles supplied loose with each coil tagged for the refrigerants they should be used with.

    It is a metering device of sorts, but not like a piston is in a resi A/C system. The refrigeration evaps are designed to operate with many different refrigerants over widely load ranges so since they have only one distributor, the nozzle in effect trims out the distributor to match the specific application. The nozzles supplied with the units are for the most common of application....a basic 35 Deg F walk-in cooler.

    If you lost the manual, here's a link:

    http://www.heatcraftrpd.com/resource...s/H-IM-64L.pdf

  7. #7
    Join Date
    Jan 2006
    Location
    Near Atlanta, GA.
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    14,513
    First off...what Ice said.

    Now, questions...

    -you indicated the superheat was acceptable, what exactly is the superheat?
    -Have you checked the actual cut in/out temps of the box? The thermostats can be wrong. Without electric defrost you can't run that box much colder than mid-thirties without freeze ups.
    -Do you have an head pressure controls on it? With no controls the head pressure could drop on cold nights and cause the TXV to not feed properly.
    -Is the evap level and does the condensation drain out properly? Did you trap the drain line?
    -What are the high/low pressure controls set at?
    -What refrigerant are you using?

    Give us some more info and we'll try to help.

  8. #8
    Join Date
    Apr 2004
    Posts
    395
    The only dumb question is one, that is not asked!!!
    Tin Knockers BANG for a living

  9. #9
    That ADT120 should use an L 3/4 in the evap. And remember how many turns in you took to try to adjust the valve.If not, run the stem in slowly as to not damage the needle against the seat then CCW it out counting the turns to maxiimum out then count your turns in to the half way point.
    FEN

  10. #10
    Join Date
    Aug 2006
    Posts
    442
    Quote Originally Posted by icemeister View Post
    Did you install the nozzle in the evaporator distributor? A missing or incorrect nozzle size is a common cause for uneven refrigerant feed that can result in icing like you describe.
    Ice you hit the nail on the head!!!!!!!!!

  11. #11
    Join Date
    Jan 2005
    Location
    Florida Keys
    Posts
    43

    Walk in help

    I would check with the manufacture to find out if this evap coil needs a external or internally equalised txv if it needs a distributer it will also need a externally equalised valve, or you could end up starving your coil of refrigerant which could also give you the symtoms you are seeing with your half iced up coil.

  12. #12
    Join Date
    Aug 2006
    Location
    st.petersburg,fl
    Posts
    803
    I'd change that differential to 5 * , sounds like thats causing the extended run. 2* diff to close.

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