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  1. #1
    Join Date
    Aug 2004
    Posts
    12
    I currently have taken over for someone who lets say was kind of a hack. I have a 401a(MP39) system with dual evap and txv's. I found the system way overcharged and txv's have been tunned almost all the way in. Is there a way to get the txv's close to factory setting by counting the turns and set them to so many turns? This system has a water cooled condenser with remote condensing unit. By the way it is a small service deli unit. If I cant figure out how to get the txv's close to factory I will probably end up replacing both txv's and adding pressure tap's after each evap. The unit only has to make it for two more months and the restaurant is shutting down permanenty. So I really don't want to install new TXV's on a piece of equipment that is going away.

  2. #2
    Count the total number of turns front seat to back seat,
    then front seat the adjustment stem to 50% of the
    total turns counted.
    Don't interrupt me while i'm talking to myself

  3. #3
    Join Date
    Aug 2004
    Posts
    12
    Thanks gerryboy00. I will give that a try tonight after the place closes.

  4. #4
    Join Date
    Sep 2001
    Location
    East Stroudsburg, PA
    Posts
    13,215
    Gerry is 100% correct.

    Click on the hyperlink that follows, for Sporlan's "12 solutions for fixing common TEV problems" brochure. It is an excellent resource.

    Also, once you set those back to the factory settings, watch them for about a half hour, and make sure that the superheat at the compressor suction service valve doesn't drop below 20 degrees, and doesn't exceed 40 degrees. Sometimes, adjustments off of factory setting are necessary for proper system operation.

    Remember, someone cranked them in. Now ya gots ta ask yerself: "How come?"

    If the valves are oversized, then you'll be fighting flooding. I doubt that they're undersized, but that, too is a possibility.

    Sometimes, even hacks have a method to their madness, Mad.
    Last edited by Educational Committee; 10-05-2008 at 10:20 AM.

  5. #5
    Join Date
    Oct 2000
    Location
    St. Augustine, FL. USA
    Posts
    46
    Someone in the Alabama area came up with the idea that putting a dime under the power head when coverting to MP-39 was the way to go.

    If you are working on equipment in this area you may want to check, few years back I ran into several Costco and BJ's that had this done.

    Likewise setting the TXV for proper design including temperature glide on MP-39, should get you where you need to be.

    Copelands statement "Compressor life of 20+ years can be expected if superheat at compressor is maintained at 20deg.

  6. #6
    Join Date
    Aug 2004
    Posts
    12
    Just got back from that nasty restaurant. I adjusted the txv's, both of them to center of adjustment. Pressures where really low and superheat was really high. Adjusted both txv's about another turn and a half and got a superheat of 12 degrees. After 45 min I checked compressor superheat and it was a little high, 33 degrees superheat. It is a long lineset for that small compressor. It looked like a 1/4 or 1/3 horse. I adjusted the txv's a little more and have 8 degrees superheat at the evap. The compressor superheat droped a little but still on the high side. I wonder why this unit has a reciever, there is no solenoid, and it is water cooled. Not to sure about charging water cooled units. Is there a trick or do you just use subcooling? Oh well I think I spent to much time on a unit that will be gone in a couple months. Will follow up in the am with amp draw and discharge temp. That discharge line seems awful hot. Had all my sensors in the box and on the evaps.

  7. #7
    Join Date
    Feb 2004
    Location
    Maine
    Posts
    483
    Is your suction line insulated? Sounds like you are picking up a lot of superheat on the way to the compressor. Water cooled condensers would be charged the same way as air cooled, just have different pressures and temps on the high side depending on water temp.

  8. #8
    Join Date
    Aug 2004
    Posts
    12
    Originally posted by jdenyer
    Is your suction line insulated? Sounds like you are picking up a lot of superheat on the way to the compressor. Water cooled condensers would be charged the same way as air cooled, just have different pressures and temps on the high side depending on water temp.
    It is insulated all the way to the compressor. Should I open the txv's a little more?

  9. #9
    Join Date
    May 2004
    Posts
    12,221
    Originally posted by mad_max3
    Just got back from that nasty restaurant. I adjusted the txv's, both of them to center of adjustment. Pressures where really low and superheat was really high. Adjusted both txv's about another turn and a half and got a superheat of 12 degrees. After 45 min I checked compressor superheat and it was a little high, 33 degrees superheat. It is a long lineset for that small compressor. It looked like a 1/4 or 1/3 horse. I adjusted the txv's a little more and have 8 degrees superheat at the evap. The compressor superheat droped a little but still on the high side. I wonder why this unit has a reciever, there is no solenoid, and it is water cooled. Not to sure about charging water cooled units. Is there a trick or do you just use subcooling? Oh well I think I spent to much time on a unit that will be gone in a couple months. Will follow up in the am with amp draw and discharge temp. That discharge line seems awful hot. Had all my sensors in the box and on the evaps.
    MP39

    The pressure and system capacity match R-12 when the blend is running in a 10F to 20F evaporator, and there is typically an 8F temperature glide in the evaporator. Applications: direct expansion refrigeration and air conditioning systems designed for R-12 or R-500; good success in any size system, minor adjustment of controls needed. Discharge pressure increases compared to R-12, also slight increase in discharge temperature, however the increases are not as severe as some other retrofit blends.

    You have a receiver because a TXV needs liquid, not flash gas, thus a receiver.

    Here is a good starting point and once set, leave it alone. It will be fine for a few months until they close the place down. This way you won't have to supertech it.

    1.Put the TXV's back in the center possition and leave them alone! Let them do their job, they are not a regulator for you to adjust out another system problem. Look at your sensor bulbs. Make sure they are mounted with in 11" of the evaperator coil outlet, have good clean contact and not mounted on a joint. Place the bulb between 2 and 4 O'clock on the suction line tightly and insulate it, then go on. You are looking for a superheat at the TXV bulb of 8* - 12*.

    2.You need to check your head pressure on this water cooled unit. You need to adjust your water pressure regulator on the condenser to 120* on a P/T chart. That should be around 195lbs/liquid pressure. This will get you close.

    3. Check your sight glass as your are dropping close to box cycle temp. MP39 is a blend and should not be 100% full, just slight bubble but a good liquid seal.

    In my opinion you have two problems if I am reading your post properly.

    1. Water pressure regulator on your water cooled condenser is not set properly.

    2. Because of #1 you are undercharged.
    Last edited by Dad; 03-06-2011 at 09:23 PM.

  10. #10
    Join Date
    Aug 2004
    Posts
    12
    I see lusker, I wish I would have done that first. The more I learn the more I realize I don't know jack. So is this a matter of velocity back to the compressor or is it just undercharged or both?

  11. #11
    Join Date
    Jul 2003
    Location
    Fort Worth, TX
    Posts
    219
    You need to check your condensing temperature and adjust the water regulating valve for a temp of 105* or 155 PSIG.

    If the head pressure is higher than that, adjust and monitor the sight glass or subcooling. If it is lower than that, adjust the valve closed and see what happens. If the head pressure rises, check subcooling. If there is no subcooling or a turbulent sight glass, add refrigerant.

    Depending on your supply water temp, you may have to operate with a higher condensing temp, say 110 to 115*.

    Adjust the superheat once this has been done.

    Good luck.

  12. #12
    Join Date
    May 2004
    Posts
    12,221
    Originally posted by mad_max3
    I see lusker, I wish I would have done that first. The more I learn the more I realize I don't know jack. So is this a matter of velocity back to the compressor or is it just undercharged or both?
    Maxie,

    You have dual coils and TXV's on a water cooled condenser with
    That discharge line seems awful hot. Had all my sensors in the box and on the evaps.
    ...a hot discharge. I don't think you are overcharged because your valves were almost pinched off. I think once your valves are open and you get your compressor superheat down you will find your sight glass low and your condensing T/P is off. So "yes" to both.

    Not that I am perfect but my experience tells me someone closed the valves due to icing on the coils, which is a common hit and run, did my best, hope this works. The TXV's should be allowed to do their job; so keep them set to the middle and go from their. I am not saying never to adjust one. There are times when you have to, with out a doubt, but only change them when there is no other way. No matter what one may think, the valve will always just pinch back to its factory setting using the power head and cage.


    The longer you stay here the more you will learn about your craft. No one here is perfect but together we are pretty darn good. The members here are great problem solvers as a collective but no one here knows everything. Those that think they do …. Well, what can I say? If I am only wrong once a day then I should wake up and smell the coffee.


    Welcome to the club my friend and get ready to be smarter than ever before
    Last edited by Dad; 03-06-2011 at 09:24 PM.

  13. #13
    Join Date
    May 2000
    Location
    Salem, WI US
    Posts
    63
    Great Post
    Betabass



    Success is to be measured not so much by the position that one has reached in life as by the obstacles which he has overcome.

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