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  1. #1
    Join Date
    Dec 2001
    Posts
    36
    Hey guys,
    I am in need of some assistance on an old supermarket rack, I wonder if anyone can help. The model# is DA4A000RCM, am having trouble with it flooding the compressors when it comes out of defrost. should mention that only 2 circuits on this one have hot gas defrost, everything else is off cycle. I have a sporlan head pressure control in the liquid line but it does not seem to be working therefore my liquid line pressure is exactly the same as the dicharge line pressure which I believe is not allowing the condensed liquid refrigerant to come back to the system until I come out of defrost. That is what I think but Ido not have any literature on this equipment so I am not really positive that I fully understand the sequence of operation. If anyone can help either with printed material or with advice it would be greatly appreciated. My fax#is 256-341-0616 & I am willing to pay for any info. Thanks Jason

  2. #2
    Join Date
    Sep 2001
    Location
    East Stroudsburg, PA
    Posts
    13,215
    I'd be more inclined to look directly at the cases that ARE hot gas defrost, and see if there is a check valve stuck open in one of them. Another possible cause could be a loose TXV bulb in one of the T.O cases.

    No defrost differential is not a really ideal situation, but it's unlikely to be the cause of the problem. Possible, but rare.

    Does this flooding occur only when one or two particulkar systems come out, or does it happen after every single defrost?

    Also, are you 100% positive that it's flooding? (Oil failures???)


  3. #3
    Join Date
    Dec 2001
    Posts
    36
    dave
    Thanks for the reply, when I went on this rack for the first time the hot gas solenoid was disconnected so I do believe that there was a problem for awhile. Also, I am very sure that the compressors are being flooded because the heads are frosting in a spot about 2"x2" for the first couple of minutes after either system comes out of defrost.After about 2-3 minutes the system settles down & works normally. This one circuit serves approx. 60 feet of meat case,about half of it is coffin style & the other half glass front. I have checked the check valves & did not find any that were sticking.I know for sure that the pressure regulator on this rack is not working & I will have to replace it anyway but I just honestly dont know if that will cure this other problem.

  4. #4
    Join Date
    Jan 2004
    Location
    Earth
    Posts
    4,879
    If you had no differential your cases would be icing. Some differental valves are de-energized for differential flow. So you would always have differential, even when the case is in refrigeration.

    Put it in defrost and do what Dave told you, look at those check valves real hard. They only need to be a little slow in reacting to the pressue change to flood you.

    Then get that Differential system working properly. The electric company will hate you for it, but the store manager may ask for your hand in marrage.


    A Diamond is just a piece of coal, that made good under pressure!

  5. #5
    Join Date
    Jul 2001
    Location
    Gold Coast of Connecticut
    Posts
    4,578
    Sounds like you only have a suction stop and someone opened up a txv all the way allowing liquid to FILL the entire system when in defrost. Was this happening when the hot gas valve was disconnected or when you re-connected it?

  6. #6
    Originally posted by jsnmrphy
    dave
    Thanks for the reply, when I went on this rack for the first time the hot gas solenoid was disconnected so I do believe that there was a problem for awhile.
    What was the reason that you were called to the store in the first place. If the hot gas valve was disconnected when you got there and the cases were not iced up I would suspect that maybe the cases have been changed from original and maybe they are no longer gas defrost cases. How long was the defrost time before ypou started messing with things. Open up 1 case and look for a check valve around the txv. If there is one then the cases are probably gas defrost. If no check valve then the cases are off cycle.

    If the cases really are gas defrost then the first order of buisiness is to get the differential regulator working. Without this valve there is nothing to move the refrigerant out of the cold evaporator and back to the main liquidline where the refrigerant is then used by the rest of the systems. Refrigerant condenses in the coil and all comes back at once when defrost is over. The differential should be set for a minimum of 35 psig across the regulator.

    Once you get the regulator working then if the problem persists then you might look for a check valve in the case that is sticking closed While this is not common it does happen. Since the flooding seems to be occuring only after defrost I would rule out any txv problems and I would rule out a check valve that is sticking open.

    Good luck. Hope you get to the bottom of the problem before you have to start replacing compressors.

  7. #7
    Join Date
    Dec 2001
    Posts
    36

    Hill Rack

    Seems as though the liquid pressure regulator was the whole problem. After I got that working I started getting my refrigerant back to the liquid manifold and have not been able to see any flooding. tink I will go back one more time after I give enough time for evaps to ice up and see it defrost again just to be sure. I really appreciate the info & technical advice from all of you.Even though I dont post very often, I read here almost daily & it has been well worth the few dollars that it takes to become a supporter. Thanks to all.
    Jason

  8. #8
    Join Date
    Jun 2001
    Location
    Michigan
    Posts
    12,077
    I am not getting your thing here. Are you saying your drop leg Hold back is cranked all the way in and your flashing to your liquid manifold?? If you got no liquid leaving the rack out the liquid manifold, how then hell can you come back with out any superheat. Plus you should have a check valve leaving your separator.

    As far as HOT GAS, did I read where your not redirecting hot gas to hot gas manifold during a call for hot gas defrost with an increased hot gas by use of a diff valve.

    Or are you saying that in hot gas, your coming back and flooding suction manifold.

    I aint sure if this might be your problem but I have a few racks where I had to ressurect. And they would flood suction. The PID on the controls was keeping my pumps off too long to react quick enough to change in suction manifold. The PID on my puters was real low. All I did was ask the controller to respond faster. Off cycles on a rack should be dealt with as well, at a minimum a cch when pump is off so your can try to prevent migration.

  9. #9
    Join Date
    Dec 2001
    Posts
    36

    Hill

    Dow,
    Sorry about the confusion, the valve that I was referring to is a liquid differential valve and is positiond at the inlet to the liquid manifold, it is used in conjunction with an electric solenoid valve so that it only operates when one of the circuits is in defrost.Its only job is to maintain a 20# pressure differential so that the liquid that condenses in the evaporator during the defrost cycle can be returned to the system.I know this is primitive but it seems to work ok as long as everything is set up & operating properly, this thing is so old I doubt that they had computers back then. Thanks again for all the help.

  10. #10
    Join Date
    Jun 2001
    Location
    Michigan
    Posts
    12,077
    Okay now I gotchya. I thought we were talkin hold back off drop leg. Sorry. My mind works, it just sometimes needs a rubber maleet upside the head.

    It aint prehistoric. I can't remmeber, Tyler maybe, they loved that way of doing it.

    I catch what your getting at. Your saying she was not energizing, creating a 20 lb diff at liquid manifold so the hot gas that get's shipped out aint flowing back to liquid manifold, rather dumping back into suction. Yeagh I guess, maybe. Something like that I can't be sure unless I am there on it.


  11. #11
    Join Date
    Jan 2004
    Location
    Earth
    Posts
    4,879
    Is that a LDR or OLDR valve?
    A Diamond is just a piece of coal, that made good under pressure!

  12. #12
    Join Date
    Oct 2001
    Posts
    16
    It sounds like there was no hot gas flow through the evaporator in defrost. When the defrost ends the evaporator goes from the high side pressure to the low side pressure right away causing liquid to rush out of the evaporators to the compressors. When you got the discharge modulating differential valve to work that caused hot gas to flow through the evaporators in defrost. After a little while the case warm up and the defrost thermostats close shutting off the hot gas valve. Now the cases sit for a few minutes doing nothing, called drip down time. When the cases go back to refrigeration the evaporator pressure is at case temp, say 55. The refrigerant doesn't flood back to the compressors.

    David

  13. #13
    Join Date
    Jun 2001
    Location
    Michigan
    Posts
    12,077
    Originally posted by davidchsw
    It sounds like there was no hot gas flow through the evaporator in defrost. When the defrost ends the evaporator goes from the high side pressure to the low side pressure right away causing liquid to rush out of the evaporators to the compressors. When you got the discharge modulating differential valve to work that caused hot gas to flow through the evaporators in defrost. After a little while the case warm up and the defrost thermostats close shutting off the hot gas valve. Now the cases sit for a few minutes doing nothing, called drip down time. When the cases go back to refrigeration the evaporator pressure is at case temp, say 55. The refrigerant doesn't flood back to the compressors.

    David
    Dave, thats what I was thinking he was saying also, but he's talking liquid and not hot gas. I have like 5 racks set up with hot gas with the flo con dishcharge mod valve. So that was what I thought he was talking about. He's got the liquid differential, where the liquid mainfold will drop in pressure, to get the hot gas flowing out to coil, coming back.

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