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  1. #1
    Join Date
    May 2003
    Location
    Ohio
    Posts
    129
    had a service call on a 3.5 ton bryant (R-22) it was sched, as a tune up but it's been pretty hot lately and wasn't cooling that good, I found: 17 degree temp drop across coil, high head pressure, but without the high discharge air temp, liquid line was around ambient temp, 86 deg, head pressure 300, suction 35: I pumped the unit down, opened up the piston, cleared the blockage, oil was spitting out from the evap side of the piston connection, I flushed out the lineset & coil with nitrogen, replaced piston, evacuated, opened up valves and restarted. system pressures were now close to normal. superheat was 15-18 deg, subcooling was still high, around 30 deg, pressures were 72 over 225, and my drop was still 17, deg, at one point the compressor almost didn't start, amp draw was less that half, of rated amps, the unit also didn't pump completely down in itself before clearing out the piston (forgot about that) I tried to pump it down again, and would not pump down, relief valve was hissing at 35 psig. so I comdemmed the compressor, non of the distribution tubes were plugged, coil is clean, airflow is good, etc, this all happened several days ago, so it's not fresh in my memory, I'll now if I mis diagnosed it when I change the compressor next week, also, the unit is only 2 years old. I've also investigated an overcharge in unit but with the low suction , and no floodback , made be beleve it not to be.
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  2. #2
    Join Date
    Dec 2002
    Location
    Houston,Tx.
    Posts
    16,004
    Compressors will sometimes do that when you have a long and big lineset 1-1/8 suction and big evap. coil the condenser just cannot contain all the charge.
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  3. #3
    Join Date
    Aug 2004
    Location
    North Richland Hills, Texas
    Posts
    14,914
    Sounds to me like you condemned a potentially good compressor.
    As mrbillpro pointed out, they will do that if you try to pump them down when there is more refrigerant in the system than the condensor can hold. Most of the time I find a system with a restriction in it, someone else has added refrigerant to it before. Sometimes it isn't "someone else", but was me adding a couple of pounds before it dawned on me that the charge wasn't the problem, usually that only happens to me when it is a clogged filter drier inside the unit though.

    What were the return air wet and dry bulb and supply air dry bulb temperatures after you cleared the restriction?

    Are you sure it has the correct piston?

    Do yourself and your customer a favor and find the real problem before you go changing the compressor out.

    If more government is the answer, then it's a really stupid question.

  4. #4
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,347
    With 30 degrees subcooling, I'd be seriously considering an overcharged condition. When you tried to pump the system down, the condenser could not hold all that refer because there's more refer in the system than should be.

    Your split across the evap coil will vary with airflow, humidity conditions, cleanliness of both coils, charge, etc.

    I agree with Mark, I think it's premature to condemn the compressor. If anything it's been having to deal with an overcharge for awhile. Bring your subcooling down closer to 10-12 degrees and see what that does for your split over the evap.
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  5. #5
    Join Date
    Apr 2004
    Location
    Midwest
    Posts
    2,683
    Something just sounds off to me…

    I wouldn’t worry too much about a 17^ drop with a fixed metering device. Depends on the load, sometimes a 10^ drop is normal.

    Honestly, sounds like there may be some sort of non-condensable in the system. Non-condensable usually give you high sub cooling. You can have high sub cooling with an overcharge but suction would be high, head would be high and superheat would be low…but your not seeing that right?

    What tends to happen is air and moisture collect in the condenser and liquid line, so when you read your head pressure you are reading more than one compound. You are actually reading the refrigerant+air+moisture; it’s a false reading.

    Usually this jacks up the head pressure but leaves the liquid line at a normal temperature creating high sub cooling.

    Is this a Scroll compressor?

    Your condemning a compressor for low pumping ability (an inefficient compressor) keep in mind an inefficient compressor with a fixed metering device will produce low superheat…again you are not seeing that.

    I would double-check some things out, no sense going through all that work to not correct the problem.

    Good luck.
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  6. #6
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,120
    Check if thats the right piston, the compressor is pumping good.

    Some type of restriction is still there, and a new compressor won't do any better.
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  7. #7
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,120
    Originally posted by beenthere
    Check if thats the right piston, the compressor is pumping good.

    Some type of restriction is still there, and a new compressor won't do any better.
    And 2 will remmember this thread when he sees that compressor.
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