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  1. #1
    Join Date
    Jun 2006
    Location
    New Jersey
    Posts
    4,330

    Scroll Shell Temps

    So I replaced 2 32hp scrolls in tandem yesterday. Ran the pumps overnight and charged her up today. Everything looked good. I did notice a slight oil leak at one of the rotolocks on the equalizer line. So I snugged it up and wiped it clean. Went through and checked SC, SH at compressors and at TXV's, amperages, oil levels, and discharge temps. All looked good. Cleaned up and thought...I should check that rotolock. It wasn't leaking, but I noticed the one fitting was warm. Actually the whole bottom of the compressor was warm.

    So I'm thinking crankcase heater is running. Nope it's off. I measure 91 degrees at bottom of compressor. I check the other compressor bottom was 61 degrees. So I verify suction and discharge temps to each compressor. Suction temps are within 2 degrees at 59 degrees and discharge temps are with 3 degrees at 170 degrees. Oil level was 3/4 on the equalizer site glass. Again, I check shell temps and the one is alot warmer.

    So I ran each compressor individuality and took readings. Readings looked good. The only thing that really changed was oil level in the equalizer sight, but with only one compressor running.....the oil sight on the equalizer doesn't really show true oil level in the running compressor. But the shells were close to suction temp.

    With all my readings good, I let her run. I will be going back Saturday to replace cores and do an acid test. But it bothers me why the one compressor's shell is so warm, when both are running. Any one have an answer?

  2. #2
    Join Date
    Apr 2012
    Location
    Paper Street Soap Company
    Posts
    2,304
    As long as you checked the amperage readings on each compressor and they're comparable plus you've confirmed you got good SH what else can you do ?

    New comps come charged with oil and you may want to make sure you dont have excessive oil returning to the new comp's.

  3. #3
    Join Date
    Mar 2009
    Location
    Mid-Mo
    Posts
    3,590
    I don't have anything wise to add, I just want to see what everyone has to say about it.

  4. #4
    Join Date
    Sep 2010
    Location
    miami,fl.
    Posts
    605
    Quote Originally Posted by ascj View Post
    So I replaced 2 32hp scrolls in tandem yesterday. Ran the pumps overnight and charged her up today. Everything looked good. I did notice a slight oil leak at one of the rotolocks on the equalizer line. So I snugged it up and wiped it clean. Went through and checked SC, SH at compressors and at TXV's, amperages, oil levels, and discharge temps. All looked good. Cleaned up and thought...I should check that rotolock. It wasn't leaking, but I noticed the one fitting was warm. Actually the whole bottom of the compressor was warm.

    So I'm thinking crankcase heater is running. Nope it's off. I measure 91 degrees at bottom of compressor. I check the other compressor bottom was 61 degrees. So I verify suction and discharge temps to each compressor. Suction temps are within 2 degrees at 59 degrees and discharge temps are with 3 degrees at 170 degrees. Oil level was 3/4 on the equalizer site glass. Again, I check shell temps and the one is alot warmer.

    So I ran each compressor individuality and took readings. Readings looked good. The only thing that really changed was oil level in the equalizer sight, but with only one compressor running.....the oil sight on the equalizer doesn't really show true oil level in the running compressor. But the shells were close to suction temp.

    With all my readings good, I let her run. I will be going back Saturday to replace cores and do an acid test. But it bothers me why the one compressor's shell is so warm, when both are running. Any one have an answer?
    just curious in wich place was the original burnt compressor in?? The one reading 91 degree shell temp or the one reading 59 degrees???

  5. #5
    Join Date
    Jun 2006
    Location
    New Jersey
    Posts
    4,330
    This unit has three 15hp scrolls in tandem on circuit 1 and two 32hp scrolls in tandem on circuit 2. I lost both 32hp's on circuit 2 and replaced. So both are new.

    The equalizer line goes across the two sight glasses. Upon removal of the old compressor, the oil level was just at the sight fitting. So with the replacements, I ended up only pulling 1 cup of oil out to match oil levels.

    All my readings showed the compressors were happy and ok, but I just don't understand how the one compressor can have such a dramatic shell temperature difference. Especially giving that the suction pressure and temps are the same, oil level should be the same, and capacity should be the same.

    I'm going there tomorrow to acid test oil and replace cores........I'll update what I find. There is another exact unit there. I'll check that as well.

  6. #6
    Join Date
    Dec 2011
    Location
    New Zealand
    Posts
    2,171
    Scrolls, can take up to 48hrs to bed in (some are better than others), it could be that the refrigerant flow passing through each compressor is different and that there may be a sight bit of back flow across the compression area. The compression part is still shifting the roughly the same mass of refrigerant, so power draw will be very similar, but the slight reduction in actual mass flow (suction port to discharge port), will cause less gas cooling of the compressor motor, so lifting the shell temp.
    I have presumed that you are measuring a similar place and that the compressor suction superheat is high enough to ensure that there is no liquid entrapment into the suction stream.
    Just one final one, listen carefully, can you hear a slight background whistle/woosh noise. The internal pressure relief valve could be passing ever so slightly. (similar results to bedding in).
    So the time you get back, it should have bedded in, so would expect to see little difference. If still the big difference, run individually, check to see if the perform equally as good as each other "net cooling effect" if not, I would recommend as a "last resort", gently close the discharge valve until the internal relief blows (should remove any crap that maybe under the relief valve seat)

  7. #7
    Join Date
    Oct 2012
    Location
    Las Vegas, NV
    Posts
    6
    I think you have one of the compressors running backwards buddy check your wiring?

  8. #8
    Join Date
    Dec 2008
    Location
    Buffalo NY
    Posts
    3,078
    Quote Originally Posted by markgarcia7uu View Post
    I think you have one of the compressors running backwards buddy check your wiring?
    If it was running backwards he would not have good readings. He would also know by the noise that it made.


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  9. #9
    Join Date
    Jun 2006
    Location
    New Jersey
    Posts
    4,330
    So a update....went Saturday to check cores and acid test. Acid test came clean. Liquid cores not too bad, but suction cores had a 12psi drop. Isolated cores. Installed pleats in suction. Liquid not pulling down. Wouldn't you know the factory liquid valve not holding. Shut down circuit.

    Monday.....pulled all 170 pounds back out and replaced liquid valve. Ran pumps over night. Return the next day. Replaced liquid cores with some golds and gassed her back up. Again verified amperage, charge, and temps on both compressors.

    With both compressors running for extended time.......the compressor on the right runs alot warmer shell temp then the other. Discharge temp, suction temp, and amperage are the same. So I setup the other condenser, at the location to run the same compressors. Same results. Right compressor runs alot warmer shell temps.

    I left it as is. All my readings say the compressors are fine. But it just bothers me, I don't understand why the right side compressor's shell is warmer?

  10. #10
    Join Date
    Jul 2006
    Location
    Virginia
    Posts
    4,607
    Are you running motor protectors on them scrolls
    We really need change now

  11. #11
    Join Date
    Jul 2009
    Location
    Columbia, MD
    Posts
    3,787
    very odd. good observation though!

  12. #12
    Join Date
    Aug 2006
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    Mixing oil and fire with a big spoon.
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    4,247
    Quote Originally Posted by gravity View Post
    very odd. good observation though!
    i know. but now i got more things to check!
    my 1st time jumping out of a plane...http://youtu.be/Kv38G0MHsGo

  13. #13
    Join Date
    Jun 2006
    Location
    New Jersey
    Posts
    4,330
    Yes, the compressors have monitors on them. They come installed on the new compressors.

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