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  1. #1
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    Walk - in freezer trouble

    I am having trouble with a walk - in freezer. I am a facilities manager working at a large prison. I recently lost my hvac tech and was forced to get my epa cert and teach myself the trade. I have done well so far but i am having trouble with a walk in and have never worked on one before.

    The walk in is a Russell refrigeration unit. The model is 8l44 with a liquid line receiver. The instructions tell me to put in 52lbs of 404A refrigerant which i have done and then put in another 23lbs of refrigerant for flooded operation so the unit can operate in any conditions. I have done this and i might have put in a couple of pounds too much. I cannot get the evaporator sh or the compressor sh to come down low enough.

    My evaporator sh is about 22 degrees. The txv bulb temp is at 21.3 degrees and the saturation temp is at -.3 degrees. Outside, my compressor sh is about 57 degrees. My suction line temp is about 50 degrees and my saturation temp at the compressor is a -7.1 degrees. I have the txv adjusted all the way out, counter clockwise, and this is as low as i can get the superheat.

    The manual says the evaporator superheat on an 85 degree day should be between 8 to 10 degrees and the condenser superheat, which is more important, should be a minimum of 20 degrees and no more than 40 degrees. I believe i overcharged the system but would like someone else's opinion on other things i could check to confirm this or find the real issue.

    Also if i did over charge the system, can i pull a little liquid refrigerant out of the system at the liquid line receiver without dumping the whole system?

    Any help is appreciated fellas.

    Thank you,
    JJ

  2. #2
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    Feb 2007
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    Uuum...73 lbs of R-404a ??? How big is the cooler ? like 20 feet by 40 by 14 foot tall ? Yes you can pull liquid out of the receiver if you have a Appion G5 twin or similar recovery.

  3. #3
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    Did you keep an eye on the SG while charging?

  4. #4
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    Quote Originally Posted by ReferTroop View Post
    Uuum...73 lbs of R-404a ??? How big is the cooler ? like 20 feet by 40 by 14 foot tall ? Yes you can pull liquid out of the receiver if you have a Appion G5 twin or similar recovery.
    Not quite but the measurements are 25'x30'x7.5'

  5. #5
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    Yes sir I did. The manual said to put in 52lbs and then add the 23lbs for flooded operation. The 23lbs was exact from a new 30lb bottle. I used four partial bottles when i put in the 52lbs and after going back and doing the math, it looks like i added 54lbs instead of 52lbs. I just didn't realized it until after i added the 23lbs. The instructions call for 52lbs of 404A which is 90% of the receiver and liquid line. The sg filled at about 45lbs. Afterwards the instructions say to add the 23lbs for flooded operation, which it needs to keep the -10 to -20 degree temp inside the walk in during the winter time.

  6. #6
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    I thought about removing 2lbs and seeing if i could get the sh down. I assumed i could remove the refrigerant from the liquid line receiver without changing the makeup of the 400 series refrigerant since i was removing it as a liquid but i wanted a professional opinion on this. I also assumed am overcharge could potentially keep me from lowering the sh to the correct temperature.

  7. #7
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    Sounds like you're overcharged but with a receiver it is doubtful that is your issue. If the TXV won't adjust open anymore you should be looking for restrictions at the FD, TXV, or solenoid... or the TXV bulb has lost some charge

  8. #8
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    High superheat is not a symptom of an overcharge. What's the subcooling and head pressure?

  9. Likes ReferTroop liked this post
  10. #9
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    How many compressors and the model #'s would help me, how many evaporators and the model #'s would help me.
    I need head pressures, suction pressures along with your already supplied temps but you could repeat them. Did you check the condenser condition (plugged), is there a headmaster ? Could be stuck open, feel the lines on it to determine flow from condenser to receiver. Pics would be good too.
    Is there a CPR valve or a EPR valve ? I'm assuming you have 15 - 30 H.P. discus copelands but I have no idea... need more info
    Quote Originally Posted by Jonjordan25 View Post
    Yes sir I did. The manual said to put in 52lbs and then add the 23lbs for flooded operation. The 23lbs was exact from a new 30lb bottle. I used four partial bottles when i put in the 52lbs and after going back and doing the math, it looks like i added 54lbs instead of 52lbs. I just didn't realized it until after i added the 23lbs. The instructions call for 52lbs of 404A which is 90% of the receiver and liquid line. The sg filled at about 45lbs. Afterwards the instructions say to add the 23lbs for flooded operation, which it needs to keep the -10 to -20 degree temp inside the walk in during the winter time.

  11. #10
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    I do not know what the sub cooling is but i can check it tomorrow. If the sub cooling is right, then i can check the txv bulb by putting it in warm water and seeing if the sh drops, correct?

  12. #11
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    Low superheat is usually common with overcharge, subcooling is somewhat irrelevant ....

    Quote Originally Posted by Red Man View Post
    High superheat is not a symptom of an overcharge. What's the subcooling and head pressure?

  13. #12
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    If you have 72 lbs. of 404a in there 2 lb.s isnt gonna make a difference one way or the other as your receiver should be able to hold at least 75 % of total charge even if undersized.

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  15. #13
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    Thread Starter
    Reefertroop

    I can get the compressor and evaperator model numbers tomorrow. Also by then i should have enough post as a new member to POST some pics. As far as the other pressures, the head pressure is about 210 with 92 degrees saturation temp. I do not have the discharge line temp. The suction pressure is about 24 with -7 degrees saturation temp at the condenser. The suction line temp is 50 degrees. I do not know what a head master, cpr or epr valves are. There is something that looks like a small grey regulator in line after the liquid line receiver. There is also a liquid line solenoid on the inside of the walk in behind the evaporator. Also on the liquid line after the filter dryer, there is a tee in the line that directly shoots liquid refrigerant back in to the compressor. I appreciate the help so far and will give more info tomorrow when i get back to work.

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