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  1. #1
    Join Date
    Feb 2013
    Location
    Champaign, IL
    Posts
    42

    compressor changeout issue...help!

    Compressor replacement the other day: American Standard 3 ton unit w a fixed orifice, R22, about 7 yrs old. Replaced line dryer and compressor, pressure tested, blew an entire tank of nitrogen through the system, vac down to below 500 microns, charged system.

    head pressure initially around 225, suction around 60. System would run for about 30 seconds, then I could hear the compressor hum slightly louder, almost like it was bogging down very slightly from liquid, then it would get quiet. As it quieted down, the pressures would both drop about 20 psi. after dropping, the pressures would begin working their way back up to the 225/60. As soon as they reached those pressures, the process would repeat.

    indoor wb about 65, outdoor temp around 80. superheat was between 0-5, changing as the pressures changed. temp drop across the evap was 17 degrees, would fluctuate with the pressures. i wondered if it was overcharged and sending liquid back to the compressor, but my suction was already low. I removed some ref, but it didn't help.

    pulled out all ref, blew more nitrogen through the system, vac down again, charged back up - same issue still happening. not sure where to go from here?

    i also noticed, when i pulled suction side hose off, after removing high side and equalizing gauges, the suction side was liquid, seemed to be liquid in the suction line...

    good airflow, clean evap coil, clean filter.

    any ideas?

  2. #2
    Join Date
    Jan 2008
    Location
    Madison In.
    Posts
    141
    Piston right size. Kinda sounds like airflow

    Sent from my SCH-S738C using Tapatalk

  3. #3
    Join Date
    Aug 2006
    Location
    Columbus Ohio
    Posts
    2,011
    0-5 degree superheat on a fixed orifice metering device, with clean filter/coil, and proper duct sizing, says "overcharged" to me.

    What are you charging by?
    UA LU189

    10mm, because it's better than .45acp

  4. #4
    Join Date
    Nov 2007
    Location
    Mississippi
    Posts
    1,352
    Overcharged. What is the indoor dry bulb?

  5. #5
    Join Date
    Feb 2013
    Location
    Champaign, IL
    Posts
    42
    I thought overcharged for sure, I removed some refrigerant but it didnt seem to affect anything. I weighed in according to factory charge on the unit, planning to fine tune according to superheat, but have never had the pressures do that. I couldn't really accurately adjust charge with the pressures rising and falling the way they were. I didn't check the orifice as far as size, the same one that has been there for 7 yrs.
    When I pulled out the refrigerant, blew nitrogen, vac down, and recharged, I went specifically according to factory charge on unit. Lineset length probably equivalent to about 30-40'. cant imagine it would have been that far overcharged. Ive had some very overcharged units not act like that - that was my initial thought though.

  6. #6
    Join Date
    Oct 2010
    Location
    Anderson, South Carolina, United States
    Posts
    7,050
    Whatever it is is what killed the other compressor. Low airflow more than likely.

  7. #7
    Join Date
    Nov 2007
    Location
    Mississippi
    Posts
    1,352
    Blower is running?

  8. #8
    Join Date
    Feb 2013
    Location
    Champaign, IL
    Posts
    42
    I will check static pressures when i go back, that's the only way i know to confirm correct air flow. the system is zoned, I believe it has bypass ductwork with low temp cutout on the board if I remember correctly. how else can i confirm proper airflow? blower is running, I have a 17 degree temp drop. we left the compressor in, I am going back to check things over next week. they said it is keeping up right now but i now it probably won't last.
    I agree, and am concerned, that what ever killed the last compressor could do the same thing to this one. if airflow seems to be the issue, i will double check that, just not sure what to do beyond checking static.

  9. #9
    Join Date
    Nov 2007
    Location
    Mississippi
    Posts
    1,352
    Low suction + low superheat = low airflow

  10. #10
    Join Date
    Dec 2003
    Location
    Citrus County, Florida
    Posts
    1,554
    model numbers, static duct pressures, subcooling will tell you if over charged, did you pul;l the condenser covers and clean the coil? also, what is the temp if the discharge compressor line? amp draw of compressor? Something killed the old compressor, was this a recip or scroll?
    Doug

  11. #11
    Join Date
    Jan 2008
    Location
    Madison In.
    Posts
    141
    Ouch zoned. I bet airflow

    Sent from my SCH-S738C using Tapatalk

  12. #12
    Join Date
    May 2013
    Location
    near knoxville tenessee
    Posts
    175
    ya, zoning a dead giveaway.
    I know everything about HVAC/R until i go to the next call.

  13. #13
    Join Date
    Feb 2013
    Location
    Champaign, IL
    Posts
    42
    i've seen low airflow cause low suction, but not the fluctuation in pressures that i was getting. the fact that the pressures would rise, the compressor would get slightly louder, then the pressures would drop 20 psig is what really confused me. it's very possible that i'm wrong, but i don't think it the pressures have been fluctuating like that for 7 yrs without issues - they have been a customer for several years, never had major issues with the cooling.
    i will check the amp draw and liquid line temp when i go back, i didn't get those. we did clean the outdoor coil as a part of the compressor changeout.
    if it has low airflow, would that cause slugging, but not continuously? is it possible that's why i'm hearing the compressor get a little louder, also possibly why i had liquid present when i removed the suction hose? i've never seen that before, but i'm all ears!

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