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  1. #1
    Join Date
    Apr 2011
    Location
    michigan
    Posts
    172

    Walk-in Cooler R409a operating pressures

    I have a medium temp., water cooled walk-in cooler which had R-12 in the system. I found the evaporator coil was full of holes, so I replaced the evaporator and txv, and after evacuating the system recharged with R-409a, as I was told this was similar to R-12, compatable with the existing oil in the compressor, only it operates at a slightly higher head pressure. I believe I have the problem with the system operation figured out, just was looking for some more insight. On start up my discharge pressure ran around 155psig, 96 liquid temp, sight glass was foamy, suction was about 58-60 with a 51 suction line. The box temp started at around 65 and after an hour to an hour and a half was at maybe 55. My water entering temp was 58 water leaving temp was 65. I removed one end of the water cooled condenser and tried to clean the water tubes best as I could, but cannot get the end plate to seal up, this is a tube in a tube type condenser with a square manifold on either end so you can clean the water tubes. After cleaning the water tubes my temps and pressures really did not change much, my discharge and suction went down a little but not much and my box temp. really isnt changing much. I have the head pressure control valve adjusted to the lowest head pressure setting either way I adjust the control the pressure and water temp stays about the same. I am in the process of getting a new condenser, and head pressure control. I believe the condenser is still scaled up to much to transfer the heat as this system is at least 30 years old and original except the parts I replaced. I thought I may be slightly low on charge as well but I pumped the system down into the receiever and after it had pumped down checked the liquid level in the reciever which was about 2/3 to 3/4 full of liquid. I did try to adjust the txv to increase the super heat, but also no changes occured, when I installed the txv I removed the head and internal parts wrapped it with a wet towel and soldered it in, so I know I didnt dammage the txv when I installed it, I know my sight glass was not clear but thought with 7-8 subcooling I should be able to get better readings than this. As I said I was looking to see if anyone else had any other ideas which I may have over looked. I have worked with 409a in the past on air cooled walk in coolers and had no problem, but this one I believe is running a little high on the high side pressure which is also causing the low side to run high and not let my box cool down better I believe if I can get my sub cooling up, get my water split up and my superheat up I believe this cooler will go for another several years.
    Any help is appreciated!
    Todd

  2. #2
    Join Date
    Feb 2005
    Location
    Tampa Florida
    Posts
    776
    Does the compressor pump down?

  3. #3
    Join Date
    Jan 2006
    Location
    DFW Metroplex
    Posts
    4,910
    I've read this a couple of times now, and something doesn't sit right.

    Am I wrong, or does SST of 409A @ 59 psig = +63F?
    "The problem is the average person isn’t tuned in to lifelong learning, or going to seminars and so forth. If the information is not on television, and it’s not in the movies they watch, and it’s not in the few books that they buy, they don’t get it" - Jack Canfield

  4. #4
    Join Date
    Feb 2008
    Location
    California
    Posts
    2,066
    I don't think a new condenser is going to fix your issue.

    At 155 PSI, your head pressure isn't all that high. And as your high load reduces, so will your head pressure.

    I think you should clear the sight glass and check your superheat.

  5. #5
    Join Date
    Feb 2004
    Location
    Western New York
    Posts
    1,053
    1) Leaving water temp out of the condenser should be about 105 deg. Sounds like you may have a bad water reg valve, but more likely with the 155 psi head, the condenser is scaled.

    2) I agree with Markettech, the suction pressure is too high... should be around 14-17 as it nears design box temp. You said you dis-assembled the TXV- did you get it back together right? Also, with a dis-assembled valve, wrapped in a wet rag, how do you keep moisture out?

    3) You should have a solid column of liquid to the TXV (clear sight glass). Torching the receiver in this case doesn't mean a lot, charge depends on the whole system capacity and the length of the lineset.

    4) The head pressure isn't all that high, and with a properly operating TXV won't affect the suction pressure that much.

    5) My guess you have a dirty condenser, bad water regulator, and an incorrect/damaged TXV. Check your superheat.
    Experience is what you have an hour after you need it.

  6. #6
    Join Date
    Jan 2006
    Location
    DFW Metroplex
    Posts
    4,910
    I was thinking about the suction being high, but what I was more confused about is how a +51F suction line temp can be achieved when our SST is +63F.

    Where exactly were you measuring the suction pressure/temperature?
    "The problem is the average person isn’t tuned in to lifelong learning, or going to seminars and so forth. If the information is not on television, and it’s not in the movies they watch, and it’s not in the few books that they buy, they don’t get it" - Jack Canfield

  7. #7
    Join Date
    May 2009
    Location
    The Pas, Manitoba Canada
    Posts
    212
    Quote Originally Posted by jimp View Post
    Does the compressor pump down?
    If it's a semi hermetic the reed valves may be leaking abit and capacity disappears. Is the compressor drawing full load amps on startup?

  8. #8
    Join Date
    Jun 2008
    Location
    Rochester, NY
    Posts
    61
    You can't check subcooling with a receiver. Just clear the glass and see how it runs before you make any adjustments to the water valve on the condenser.

    59 psi is a high suction for a 65 degree box. As said above, pump the system down and see if the compressor holds.

  9. #9
    Join Date
    Apr 2011
    Location
    michigan
    Posts
    172
    I did pump the system down, it pumps down and shuts off but after a few min. the suction pressure does creep back up and go through another pump down cycle, also the low pressure cut out is still set for the R-12 set up I was going to adjust the low pressure cut out as I got the box temp where I wanted it.

    As far as the compressor drawing FLA on start-up I haven't checked that yet, was going to but was trying to figure out why my press/temps didn't look correct.

    I was measuring the super heat temp at both the compressor and at the outlet of the evap. Both temps were with in a degree or two of each other. I also checked the suction temp at the compressor.

    I agree the condenser is scaled as I said I cleaned it as best as I was able to and my discharge pressure dropped about 10-15 psi, but my water temps still were less than 10 diffirencial. I did re-assemble the txv correctly and to keep out moisture I tried to mainly wrap the wet rag around the stub and the body of the valve and kept the rag as far from any of the openings on the valve as i could. Another thing I tried was in one side of this cooler is a door leading into a walk in freezer. I opened the door from the freezer into the walk in cooler and got the box temp down to around 40 my suction did drop to I think around 20psi, discharge was about 115 psig, but as I closed the freezer door the walk in cooler temp and pressures came back up to 50-55 in the box. My idea by torching the reciever was just to see how much refrigerant i had in the system i agree it depends on capacity and lineset length which in this case the line set is only 15 feet. I did check the superheat both at the txv and compressor and only had 2-3 degrees, but my sightglass was not clear.

    I greatly appreciate all of the replies and help, from here i think i will add more refrigerant to try and clear the sight glass, and check my superheat and subcooling, i was concerned with having to much refrigerant in the system already. It sounds like I may be correct on the condenser being dirty and/or the water valve not working correctly, and possibly weak suction valves, but before I go into that I will clear the sight glass and see where my readings go from there. It may be week or so before I get back on this cooler to work on it as it is more of a spare cooler but I will post my results when I get it tuned in.
    Thanks again,
    Todd

  10. #10
    Join Date
    Feb 2004
    Location
    Western New York
    Posts
    1,053
    Quote Originally Posted by Toddbrewster View Post
    I did check the superheat both at the txv and compressor and only had 2-3 degrees, but my sightglass was not clear.
    Superheat should be around 20-30 deg- I still say it's the TXV... you are flooding back to the compressor. In your first post, you said you tried to adjust the TXV, but there was no change in superheat or suction pressure.

    Also, you can't check superheat at the TXV, but I think you meant coil outlet.

    Good luck, let us know.
    Experience is what you have an hour after you need it.

  11. #11
    Join Date
    May 2009
    Location
    The Pas, Manitoba Canada
    Posts
    212
    Worked on old rail passenger a/c's that ran R12 and had to be updated and thats where R409 dropped in nice. To get walkin cooler temp to do the same thing using MP39 worked better.

  12. #12
    Join Date
    Apr 2011
    Location
    michigan
    Posts
    172
    Yes I probably said I checked superheat at the txv, sorry, I did check it at the evaporator outlet. And as I said it may be a week or so before I get back on this cooler but I will post what I come up with thanks for the help!

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