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Thread: purge on cvhe

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  1. #1
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    purge on cvhe

    Got a cvhe that had high pump out mins. and a nasty surge starting as soon as it started to load. Contractor recommended pulling charge, which showed machine to have lost 300 pounds of 1000 pound charge. Vacuum was pulled down to 430 microns, and rose less than 200 microns over the next 17 hours. That says tight machine to me. Virgin charge was weighed in, and machine purrring like a kitten now at full load; however, purge stated cycling immediatley as if air were present. temp sensor on purge was verified accurate - pumpout happening as it should. Superheat is dropping just like it would if non condensibles were present. Charge on purge was checked by subcooling per IOM - ok. Gas inlet from condenser was valved off; purged continued to cycle as before. Contractors theory is that purge is leaking the 134 a into the purge tank, which is reducing the evaporating surface and lowering the superheat. Not sure if I agree with that, but I cant think of another scenario which would explain what we are seeing. Any of you guys seen this before?
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  2. #2
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    Sounds like you could possibly have a leak on the R123 side of the purge... I would say to valve off the purge from the chiller and leak check the R123 side of the purge... When they leak checked the chiller, and pulled the vacuum, the purge was valved out of it. That's where I would start as it doesn't sound like the R134A circuit is leaking. Sounds like the purge is operating fine.

  3. #3
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    Quote Originally Posted by FacilityPro View Post
    ...Vacuum was pulled down to 430 microns, and rose less than 200 microns over the next 17 hours....
    you still have a leak...maybe not huge, but you have a (or some) leak.

    after adding charge, you will get air in the chiller...let it settle out for a couple of days and then re-check. the leak may be in the purge as stated before. i have never had a leak on the R134a side into the tank...it is possible but highly unlikely.
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  4. #4
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    Valve off the gas inlet and you have nothing left to superheat what's in the tank. A properly operating purge will have no choice but to run based on the burned in control algorithm. The only thing that will override this is if there is a leak on the purge or purge piping itself, or the solenoids are leaking into the tank.

    Since it takes proper charge to cause the evap sensible temp to drop and the 134A side of the purge holds approximately 8 ounces of refrigerant, how long do you think this thing is going to continue to be able to leak from hi to lo pressure and cause a false purge? I've had two purifiers leak in the refrigerated coil, so I can assure you that condition ain't gonna last long.

  5. #5
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    Make sure drain line is open back to condenser, if liquid can't drain out hot gas will continue to condense filling tank and continue to drop in temperature until temperture sensors turn on pumpout.
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  6. #6
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    134A side of the purge holds approximately 8 ounces of refrigerant,

    yep thats what makes me doubt that theory, among other things. The plan is to isolate the purge from the chiller and pull a vacuum on the purge. I'm waiting to see the results of that, but it's not going to prove thier contention if it leaks because it could still be on either side. They want to change the purge, but I think I'll have to see a pressure test on the 123 side before I'll buy into it. Thanks for all the help, guys - let me know if anything else comes to mind
    fp

  7. #7
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    Quote Originally Posted by sargent york View Post
    Make sure drain line is open back to condenser, if liquid can't drain out hot gas will continue to condense filling tank and continue to drop in temperature until temperture sensors turn on pumpout.
    If the drain line back to the condenser is valved out, the purge will trip on high liquid level... It's the non condensables that cause the suction temperature to fall below the pump out set point, which is 18 degrees. Simply condensing refrigerant (only) should not cause a pump out... If you can get your hands on a temperature probe, check temperatures in the following locations: Discharge line (around 140 degrees normal), liquid line (around 75 degrees normal), leaving txv (around 0 degrees normal), and place on suction line and watch to ensure that the temperature is actually getting down to 18 degrees when unit pumps out. Also at my company, when we leak check a centrifugal, we use hot water to bring the pressures up. We start going over the machine with a sniffer as soon as we hit 2psi, and we never let the machine get over about 8psi in the process as your burst disk is designed to burst at 15psi... These are my thoughts on it... The above temperatures are quoted out of the IOM for the purifier purge, and are set for ideal environments, 70 degree ambient with 8psi chiller condensing pressure. One other thing, is anyone logging pump out minutes over a 24 hour time frame? When the original leak check was performed, did the technician bypass the pump out orifice in order to allow more non condensables to be evacuated to the canister, quicker? You don't want to leave that on there indefinite, but just temporarily to assist with getting the machine fully operational.

  8. #8
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    Purge purging problems

    Guys I know you wanted to close the thread, but Trane did have a service bulletin about this very problem with the purge going into pump-out erroneously. Yes, it does the 18*F and 23*F pump-out start and stop, but it is not caused by a chiller leak. I don't remember what the SB number is. If you were able to achieve that vacuum level it is not chiller related. I am sure any of out profound Trane techs could locate it. Good Luck- GEO
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  9. #9
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    Quote Originally Posted by ga1279 View Post
    Guys I know you wanted to close the thread, but Trane did have a service bulletin about this very problem with the purge going into pump-out erroneously. Yes, it does the 18*F and 23*F pump-out start and stop, but it is not caused by a chiller leak. I don't remember what the SB number is. If you were able to achieve that vacuum level it is not chiller related. I am sure any of out profound Trane techs could locate it. Good Luck- GEO
    That would be PGRC-SB-2, unexplained purge pumpout was an issue on some pre 1997 purifyer purges. The bulletin does run through some of the causes for pumpout occurring without non-condensables in the chiller, most are covered in the preceding threads.
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  10. #10
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    Purge soleniods are common leakers. The purge orifice could be plugged up not allowing it to vent.
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  11. #11
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    You say that it pulled down to less than 1/2 mm hg absolute, and the leakback rate is less than 1/4 mm hg in 24 hours? I'm not seeing a leak in those numbers. Then again, you're using a gauge that has batteries in it.......

  12. #12
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    Then again, you're using a gauge that has batteries in it.......

    Yeah, and it wouldnt be the first time I was lied to by a VG 64; oil in the transducer,etc. My problem is that I retired from the field, and I'm working as an engineer in a hospital which means the extent of my tools doesnt go much beyond a 4 way screwdriver and a pair of channel locks. The guys on the job are competant, but it's thier tools, thier ballgame, etc. You're right about losing the superheat by valving off the condenser gas, too. but I guess it doesnt disprove thier theory, just guarantees the purge is going to run. Kinda walking a fine line here - dont want to insult these guys, especially since I dont know the answer either. I was just looking at the thing again, and the only valves on it are the soleniods between the tank and the pump and the isolation valves, which were open during the evacuation. I'm thinking that means we leak checked the 123 side all the way to the leaving side of the purge tank. Agree?

  13. #13
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    You had a vacuum drop test performed, and it included the chiller side of the purge.

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