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  1. #1

    Confused TXV issues on a multi evaporator system

    Ok, this ones been a weird one.Its a medium Temp r22 system. I have a Kramer Condensing Unit with a 4dr3r28-mo (189000 BTU) Copeland Compressor. It has 6 evaporators 31000 BTU each(low profile). It will not come down to temp. We found that 2 of the evaporators were just rotted out so we changed those. Also had one with a TXV Bad (No superheat) Had a few fans out but not enough to do what this ones doing. On the ones we just installed the brand new TXV's (SBFVE-b-c) are doing the exact same thing. Superheat is about 45 on both of them and will not adjust down any. On one we replaced the orifice in the distributor nozzle from a 2 to a 2 1/2 (both inside the guidelines of the manufacture). This changed nothing. The Room will get down to about 58 at night and today while I got these numbers it was around 62. Ok....The Compressor superheat was 45. The subcooling was 8. The sight glass at the receiver was cleared. Low psi was 42 and the high was 245 psi (90+ ambient). Superheat on other evaps were all good (12-15 range) the discharge line was around 90. Oil pressure is about 55. Discharge Temp is about 225. We changed the driers twice just too make sure. This is a cut room at a meat processing plant and there are about 40 people in it at one time. They wont shut down the room where we can get in there but only an hour or so at a time. We installed the evaps on the weekend but it was lucky because usually they work even on those days as well. Im lost and dont know what else to do. I know Im missing something and its probably simple but Im either to frustrated to see it or Im overlooking it. Any help would be appreciated.

  2. #2
    Join Date
    Jul 2012
    Location
    Western KY
    Posts
    1,221
    Are the 2 fan coils in question at the end of the pipe run, furthest from cond unit? 45 SH on these 2 and the other 4 all spot on I'm looking at my piping then my charge. Electronic sight glass is awsome on these set ups. If nothing jumps out at you on the piping I Would verify full column of liquid at TXVs, electronic sight glass. Assuming all the issues you mentioned have been corrected, fan motors and such. Starving these 2 it seems. Had similar issue a couple years ago. Ended up finding a drier on top of the box burried under insulation. Nice and frosty when I found it. Apparently it didn't want to be a drier anymore and figured it give the metering device gig a shot. Pulled it and everything made sense agin. Good luck.

  3. #3
    I was going to put some site glasses at txvs tomorrow. I couldnt do it today because they wouldnt let me sweat it in while they were cutting meat. its been a nightmare just from that fact alone. Thanks for the tips though. Anything would be appreciated right about now. lol

  4. #4
    Join Date
    Sep 2010
    Location
    Western, MO
    Posts
    871
    I'm too brain fried to think of anything to help you right now. I had a two evap system kick my butt this afternoon so I'd hate to have to see that system right now.

    All I can think is to look at it from the beginning. You need evaporator temp, you need airflow... can you start at each evaporator and see what you are loosing?

    jim
    Common sense isn't very common anymore.

  5. #5
    Join Date
    Jun 2007
    Location
    Williamsport, PA
    Posts
    165
    I was going to put some site glasses at txvs tomorrow.
    That is what I would do, found a few piping issues that way.

  6. #6
    Join Date
    Oct 2008
    Location
    Ohio, USA
    Posts
    177
    I would look at:

    • Compressor Efficiency
    • Verifying you have pure liquid getting to each TXV


    Once you know these two things, it will be much easier to proceed.

    If I read your post right, you have 4 units of the 6 working well? I'm rather surprised you could not get below 58* during the night.

  7. #7
    Join Date
    Jul 2012
    Location
    Western KY
    Posts
    1,221
    Quote Originally Posted by hwebb54 View Post
    I was going to put some site glasses at txvs tomorrow. I couldnt do it today because they wouldnt let me sweat it in while they were cutting meat. its been a nightmare just from that fact alone. Thanks for the tips though. Anything would be appreciated right about now. lol
    Tiff makes a good electronic sight glass. It's a very good and useful tool. Picked mine up at local jonstone a few years ago. Tool costs a little but pays for itself on multi evap systems. Cheeper the sweating in sight glasses. I use the heck out of mine. Hasn't failed yet. Good luck.

  8. #8
    Join Date
    May 2003
    Location
    Utah
    Posts
    733
    Quote Originally Posted by Jared Fetter View Post
    I would look at:

    • Compressor Efficiency
    • Verifying you have pure liquid getting to each TXV


    Once you know these two things, it will be much easier to proceed.

    If I read your post right, you have 4 units of the 6 working well? I'm rather surprised you could not get below 58* during the night.
    I would add to the list:

    Make sure there is no abnormal amount of suction line pressure drop (plugged filter or filter-drier, or even undersized suction line). That's a definite hit on compressor capacity.

    Make sure that the compressor capacity you've stated is from the Copeland performance charts.

    If this is a relatively new account, it's always possible that it has never operated properly....maybe a design issue from day one.

  9. #9
    The day I put on the site glasses I had a full head of liquid into the txvs. I went home and done some reading and thank god I finally figured it out. I just had the TXV closed off too much. I forgot that you cant check evap superheat with the room not even close to design temp. I just closed off the txv's on all evaps and opened them back up to factor settings, let it sit a day and then went back and it was 45 degrees in the room. Went back to all of the evaps and then did the superheat. Big thanks to Author Dick Wirz (Commercial Refrigeration for Air Conditioning Technicians) If you read long enough in these books....you're bound to stumble on something you had forgotten about. lol Thanks to all who replied on this thread.

  10. #10
    Join Date
    Jun 2012
    Location
    Northern NV
    Posts
    155
    Are they all the same temp? If not, look for an EPR valve problem.

    I did like the idea of a hidden F/D.

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