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  1. #1
    Join Date
    Sep 2003
    Location
    Western PA
    Posts
    1,354

    evaporator freeze up

    Went on a call today to check out a walk-in freezer. And let me tell you that I have little or no experience with walk-ins. And as usual, the dispachter fails to tell me that I'm the fourth tech there in the last week. Maintanence director is mad and wants answers.

    Condenser: Kolpak M768020
    PR249LOP

    Evaporator: Heatcraft LET090BSWJ
    D97J01078


    I sat down and read the last three service reports. They are as follows.
    Tech 1 arrives and finds frozen evaporator. He diagnoses a slow evep fan. He thaws and changes one fan.

    Tech 2 arrives and finds frozen evap and diagnoses low on refrigerant. He thaws unit and recommends replacing unit.

    Tech 3 gets called out last night. He finds frozen evap and thaws unit. Writes on service order that we will return to check defrost tmer and heaters.

    So they send me out to follow up and do we look bad. Now like I said, I have very little experience with walk-ins and my Service Manager knows this and he does't answer his phone. WTF. So I'm assuming that this is a pump down unit. Are they all pump down systems or not? I advanced the timer and it didn't pump down. So now I change the timer. The timer is replaced with the same D-Frost-O-Matic 8145-20-OEM. When I advance timer it does not pump down. I get Tech 2 on the phone and he says maybe it's not a pump down system. He says check amp draw on terminals 3 and four on timer. I have amps on 4 but not 3. I'm lost and need help.

  2. #2
    Join Date
    Sep 2006
    Location
    Chicago
    Posts
    474
    Number 3 on that clock is the normally open switch and number 4 is closed.

    When the timer advances into defrost 3 will close energizing the defrost heaters and 4 will open closing the normally closed pump down solenoid and shut down the fans. X is the defrost termination.

    So it is supposed to turn on the heaters, close the pump down solenoid, turn off the fans. Commence defrosting. When frost clears and temp rises 3 way switch sends power to the X terminal to terminate defrost. System starts then when the evap gets cold the other side of the three way switch turns the fans back on.

    If it doesn’t work like this find out why. Should be easy if you know the logic.

    Also only advance the clock until you hear one click if you go to far you will jump past it. It most likely is pump down so when defrost comes on it should pump down if wired and is working correctly. Ive seen some systems like this set up to defrost once a day.
    Last edited by dangpgt97; 05-28-2008 at 08:20 PM.

  3. #3
    Join Date
    Feb 2005
    Posts
    281
    yes,should be liquid line solenoid and pump down

  4. #4
    Join Date
    Dec 2007
    Location
    anywhere I want to
    Posts
    164
    Look for a pump down solonoid on the liquid line. Check for power to it, make sure it is closing. As you move the thermostat above and below setpoint you can hear it click. Unit should pump down above setpoint on thermostat and hold. If it is bypassing, it will cycle the condensing unit on/off and cause a freezeup. Heaters pull amps on #3, the second click on the defrost clock. This is not the only possibility for freezup but if its not pumping down, should be checked.

  5. #5
    Join Date
    Jul 2007
    Location
    Chino, CA
    Posts
    40
    terminal #4 should be your N.C. (solenoid or compressor) and #3 N.O. defrost heater contactor. if the wire on the #4 (N.C.) terminal on the timer is going to a liquid line solenoid then more than likely it is a pumpdown system. if so you can check if the solenoid actually de-energizes or closes when you advance the timer into defrost. if so maybe the solenoid is stuck open or if it has a manual stem someone forgot to put it back and prevents the unit to pump down.

    hope this helps

  6. #6
    Join Date
    Apr 2001
    Location
    Camel City, NC
    Posts
    6,232

    what they said and

    It sounds like you have a bad termination switch on the coil. This causes the clock to terminate on the X wire terminal when you try to put it in defrost. Only argument is that the fans would not run inside the freezer. They are suppose to delay after defrost as others said. Could have a bad/shorted X wire or swollen coil holding the solinoid plunger up too. Remove X and try to put in defrost if no go check the solinod in the back of the clock.
    Be safe not fast. body parts don't grow back

  7. #7
    Join Date
    Aug 2002
    Location
    Southold.calm
    Posts
    5,429
    Quote Originally Posted by targetman View Post
    Went on a call today to check out a walk-in freezer.
    Tech 1 arrives and finds frozen evaporator. He diagnoses a slow evep fan. He thaws and changes one fan.
    He’s full of S#!t there are no slow fans.

    Tech 2 arrives and finds frozen evap and diagnoses low on refrigerant. He thaws unit and recommends replacing unit.
    Is he working on a commission?

    Tech 3 gets called out last night. He finds frozen evap and thaws unit. Writes on service order that we will return to check defrost tmer and heaters.
    He knows less then tech 1 but at least is honest.


    So they send me out to follow up and do we look bad. Now like I said, I have very little experience with walk-ins and my Service Manager knows this and he does't answer his phone.
    Targetman

    Welcome to the Dark Side: commercial refrigeration.

    First off no one should be sending you on a call like this with little or no experience, and from the post you’ve made you know better then the 3 prior techs they’ve sent. You’re asking questions. Good for you.


    To answer your question, No not all units are pump-downs.

    Put the clock in defrost. #4 is compressor. #3 is de-frost.

    For tonight we’ll keep it simple.

    Keep asking questions. This is after all a site for learning.

  8. #8
    Join Date
    Sep 2003
    Location
    Western PA
    Posts
    1,354
    Thanks so much for your help guys. Techs 1 and 2 have been employes of the month for the last four months. They fix nothing and always sell new units. I don't want to be a parts changer.

    The unit does have a solinod and it does not de-energize when I advance the timer. I did advance the timer a couple of hundred times. Well maybe more like less than ten, did i shoot myself in the foot by doing that?

  9. #9
    Join Date
    Sep 2006
    Location
    Chicago
    Posts
    474
    There are slow fans. I replaced 2 identical fasco fans 2 years ago and I went on a pm this year to find one of the fans spinning slower. Cant say I’ve seen this on evaps but have a few times on condenser coils. Its just bearings starting to drag and soon the fan wont start. I actually have one in my van right now that was a slow spinner I use for emergency calls.

    I would go back there with the knowledge gained and crank the thermostat up and wait to see if it pumps down. Its not instant. If it dosent you know the selenoid is stuck open and thats your problem. If it pumps down start checking voltages on the clock and like others have said disconnect X to rule that out.
    Last edited by dangpgt97; 05-28-2008 at 09:21 PM.

  10. #10
    Join Date
    Dec 2007
    Location
    anywhere I want to
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    164
    [QUOTE=pecmsg;1872925]He’s full of S#!t there are no slow fans.


    Maybe he is but I've replaced fans that were not turning at full speed.


    Also put an amp clamp on solonoid coil wire to see if coil is drawing when thermostat is moved up and gauges to watch pressure
    Could be as simple as a bad coil. Wouldn't that be great??

  11. #11
    Join Date
    Sep 2003
    Location
    Western PA
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    1,354
    Guys, please explain the operation of the thermostat. I was told that it was called the defrost termination t-stat. I did not adjust the thermstat will I was there. I was suspecting a bad solinoid.

  12. #12
    Join Date
    Dec 2007
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    anywhere I want to
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    The thermostat opens and closes according to temp of box. It will be marked in degree graduations. When closed you will get 0 volts across the two terminals, when open you get a voltage reading of usually 115v. When closed the pump down solonoid will get voltage and open, allowing refrigerant to pass thru. When temp is reached, it opens and cuts voltage to solonoid, causing it to close off the flow and pump down the system till it reaches a low pressure cut out range controled by the low pressure switch, resulting in it opening and shutting power to condensing unit off. As temp in box rises thermostat will close, solonoid will open, pressure will rise, pressure switch will close and condensing unit starts up.
    I think thats about it.

  13. #13
    Join Date
    Mar 2008
    Location
    North Queensland, Australia
    Posts
    1,051
    Quote Originally Posted by targetman View Post
    Guys, please explain the operation of the thermostat. I was told that it was called the defrost termination t-stat. I did not adjust the thermstat will I was there. I was suspecting a bad solinoid.
    OK target, if it is indeed a defrost termination t'stat, it could be a 3 wire bi-metallic disk mounted on or near the coil (evaporator). Look for an aprox 3/4" round by 1" high cylinder with 3 wires coming out of it. 2 wires would be the heater protection T'stat. Look in the same enclosure as your TX valve or capillary if it's a cap system.

    When the coil is below about -5C it will supply a neutral for the evap fans. above about +12C it will switch over and supply a neutral for terminal X on your defrost controller which will energise a relay in it that'll terminate your defrost. note: my temperatures are in Celsius. I'm to bloody lazy to do the conversions for you

    If it's faulty either your fans won't run or your defrost will terminate on time only and your fans will start up as soon as the defrost terminates. That's if we're talking about a 3 wire bi-metallic thermostat.
    These are often used in conjunction with the 2 wire heater safety T'stat that will kill power to the heaters directly to protect them from a welded contact or some similar fault. If it's stuffed the fans and the compressor will stop, but the heaters won't work.

    During defrost the evap shouldn't pump down on a low temp system. The coil should have liquid in it to help transfer the heat from the heaters.

    In normal operation the room thermostat should cycle the LLSV to pump down the evap and cause the compressor to cycle off on LP.

    The defrost timer should stop the compressor and de-energise the LLSV at the same time.

    Now, slow fans. If the fan is a PSC motor (permanent split capacitor) and the capacitor looses capacitance (say a 6Uf cap meters out at 4Uf) the fan will run slow or even be sucked backwards or trip it's internal O/L. If you replace the cap it should run OK. If not replace it.

    also, check this out

    try talking to the people at your supply house. A lot of them are quite knowledgeable and willing to help out over the phone if you're a regular customer. It's not what you know, it's who you know. build up a list of contacts phone numbers as you go. I find bribery and corruption works well with a lot of these people so if they help you out don't fail to buy them a beer next time you see them.
    Good luck
    Mistakes are a part of being human. Appreciate your mistakes for what they are: precious life lessons that can only be learned the hard way. Unless it's a fatal mistake, which, at least, others can learn from. Al Franken, "Oh, the Things I Know", 2002

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