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  1. #1
    Join Date
    Apr 2012
    Location
    Central Pennsylvania
    Posts
    6

    Low-temp freezer will not reach setpoint

    Good Evening,

    I am a licensed HVAC&R Tech with 11 years experience, but I do not have a lot of experience with walk-in freezers. I am new to this forum.

    I have a small 6X6 that will not reach a setpoint of -15 degrees. To the best of my knowledge the unit was maintaining temp before a compressor failure 3 days ago. I was able to get an exact replacement for the compressor. After intallation, it pulled down very slowly, but there was a good deal of moisture in the box (floors and walls) and it has been very humid (around 70 percent with temps in the high 80s to low 90s). With all of the moisture, I was not too concerned that it was pulling down a bit slow, and I was at the end of the day.

    I checked on the unit this morning, after 14 hours of run time, and it was hovering around 9 degrees. By this afternoon, a full 24 hours running, it never went lower than 2 degrees. I was replacing a compressor on another unit - so I did not have much time to check this one out again. I did get the following information:

    -15 Ice Cream Freezer - R-404A

    Box Temp: 2 degrees

    Suction Pressure: 20 psig (Sat. of -15 degrees)

    Ambient Temp around condensor: 95 degrees

    Discharge Pressure: 330 psig (Sat. of 124 degrees)

    Suction Line Temp at Compressor: 32 degrees (it is not very easy to get a temp at TXV bulb while it is running as you have to drop the fan housing to get to it)

    Compressor amp draw: 9.5 (Rated RLA of 11.4)

    I also did try to do a quick pump down (but it is not a pump down system - just to clarify) to check the compressor even though it is new. It took a few minutes to even approach zero, and I could not wait long enough for it to get all the way down (which it did not).

    Any suggestions? I am just stuck, and I find it hard to believe that a new compressor is bad.

    Thanks.

  2. #2
    Join Date
    Apr 2012
    Location
    Central Pennsylvania
    Posts
    6
    I realize that I posted this in the wrong place. Sorry - I was pretty tired.

  3. #3
    Join Date
    Mar 2007
    Location
    NW AR
    Posts
    2,478
    You need to get your superheat dialed in. As close to the bulb as you can get.

  4. #4
    Join Date
    Aug 2006
    Location
    st.petersburg,fl
    Posts
    805
    Need more info.... model numbers
    Isn't sanity just a one-trick pony anyway? I mean, all you get is that one trick, rational thinking, but when you're good and crazy, well, the sky's the limit!

  5. #5
    Join Date
    Sep 2008
    Location
    Western PA
    Posts
    25,855
    Quote Originally Posted by minghex View Post
    I realize that I posted this in the wrong place. Sorry - I was pretty tired.
    It is in the correct forum, now.


  6. #6
    Join Date
    May 2011
    Location
    CA
    Posts
    123
    I don't have as much experience as most other guys here, but...

    Isn't your suction pressure a little high? You should set it 7-10 degrees *cooler* that your walk in's set point. You should have a suction psi of about 13...not 20. I think...

  7. #7
    Join Date
    Feb 2004
    Location
    Western New York
    Posts
    1,063
    Quote Originally Posted by minghex View Post
    I also did try to do a quick pump down (but it is not a pump down system - just to clarify) to check the compressor even though it is new. It took a few minutes to even approach zero, and I could not wait long enough for it to get all the way down (which it did not).
    Thanks.
    There is one red flag- you should be able to pull into around a 12-15" vacuum and hold it with the compressor off.

    Both suction pressure and superheat seem to be high.
    Experience is what you have an hour after you need it.

  8. #8
    Join Date
    Oct 2003
    Location
    tidewater, va
    Posts
    2,147
    the old method of pumping a compressor down into a vacuum to gauge its condition can be misleading sometimes. your best next step on this compressor is to get the model number, get a compressor performance chart for it (if it is a copeland you can get it off the web, or your supplier of that compressor can provide it) plot your suction and discharge(at the compressor) and compare amps to see if it is efficient. I remember once having a brand new ice cream freezer compressor that took a while to pump to 4 inches and i thought it odd, but a compressor curve showed its plotted readings dead on and it was way out of its operating parameters even close to 4 inch vaccum suction.
    Is your sight glass clear?

  9. #9
    Join Date
    Sep 2008
    Location
    Western PA
    Posts
    25,855
    Quote Originally Posted by r404a View Post
    the old method of pumping a compressor down into a vacuum to gauge its condition can be misleading sometimes. your best next step on this compressor is to get the model number, get a compressor performance chart for it (if it is a copeland you can get it off the web, or your supplier of that compressor can provide it) plot your suction and discharge(at the compressor) and compare amps to see if it is efficient. I remember once having a brand new ice cream freezer compressor that took a while to pump to 4 inches and i thought it odd, but a compressor curve showed its plotted readings dead on and it was way out of its operating parameters even close to 4 inch vaccum suction.
    Is your sight glass clear?
    Emerson has a program that can do that for you in real time.

    Emerson Product Selection Software

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