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  1. #1
    Join Date
    Jul 2013
    Posts
    13

    Carrier rooftop unit - high suction, low head pressure

    Hi all,
    I'm new to this forum so I'd figured I would give it a shot.

    Today I repaired a leak on a unit and replaced the filter drier (leak on a fitting in the condenser). When I charged the unit with the factory charge of 7lb 8oz (as per nameplate) I began to check some Temperatures and pressures. I was receiving a suction pressure of 95psi and a head pressure of 180. I thought at first it was my compressor valves (tin can recip) so I covered my condenser coil and saw my pressure raise. So I new it wasn't my compressor, I checked the second stage which was working 2 weeks ago when I performed maintenance and it was having the same issue with the pressure. So the issue I believe is related between both stages.

    Here are a few numbers that might help
    Suction - 95psi
    Head pressure - 180psi
    10F over Evap coil (75-65F)
    5F over evap coil when running stages one at a time (75F-70F)
    10F superheat per stage
    No temperature rise over filter driers


    If ante has any idea that would be great.

  2. #2
    Join Date
    Feb 2011
    Location
    Sacramento, CA
    Posts
    147
    What type of metering device? How is the airflow across the evap? What's the sub cooling? Amp draw on each compressor?
    I have done so much with so little for so long, that now I can do almost anything with nothing at all.

  3. #3
    Join Date
    May 2000
    Location
    Salem, WI US
    Posts
    61
    I agree with Gocolts however you may want to verify your suction readings with another gauge if you haven't done so. The temps and pressure you indicate are a little strange. I am a summing the refrigerant is R22......
    Betabass



    Success is to be measured not so much by the position that one has reached in life as by the obstacles which he has overcome.

  4. #4
    Join Date
    Jul 2013
    Posts
    13
    Amp draw
    Compressor 1: 5.1
    Compressor 2: 5.3
    LRA: 5 (but they are both pumping so I find that kinda odd)

    Metering device: fixed Orfice
    Airflow:
    Condenser coil: single coil, fins straight, just cleaned it on maintenance

    Evaporator coil:
    Clean, brand new filters.

    Supply/return ducts: have not checked sizing as it has worked previously.

    Refrigerant: R22

    Also, what

  5. #5
    did you zero your gauges and was the economizer open

  6. #6
    Join Date
    Jul 2013
    Posts
    13
    Quote Originally Posted by andhereweare View Post
    did you zero your gauges and was the economizer open
    I zero my gauges, and I checked them against another set, my economizer was closed.

  7. #7
    Join Date
    Jan 2010
    Posts
    6,099
    [QUOTE=Jordan615;16334291]
    LRA: 5 (but they are both pumping so I find that kinda odd)

    LRA (locked rotor amps) 5

  8. #8
    Join Date
    Jul 2013
    Posts
    13
    [QUOTE=VTP99;16336051]
    Quote Originally Posted by Jordan615 View Post
    LRA: 5 (but they are both pumping so I find that kinda odd)

    LRA (locked rotor amps) 5
    But if it was locked up wouldn't it not be pumping at all? Also if a compressor valve was gone wouldn't it lower my amp draw?

    I can't see both compressors being gone?

  9. #9
    Join Date
    Oct 2011
    Location
    Chicagoland Area
    Posts
    4,512
    [QUOTE=VTP99;16336051]
    Quote Originally Posted by Jordan615 View Post
    LRA: 5 (but they are both pumping so I find that kinda odd)

    LRA (locked rotor amps) 5
    Officially, Down for the count

    YOU HAVE TO GET OFF YOUR ASS TO GET ON YOUR FEET

    I know enough to know, I don't know enough
    Liberalism-Ideas so good they mandate them

  10. #10
    Join Date
    Oct 2011
    Location
    Chicagoland Area
    Posts
    4,512
    [QUOTE=Jordan615;16336591]
    Quote Originally Posted by VTP99 View Post
    But if it was locked up wouldn't it not be pumping at all? Also if a compressor valve was gone wouldn't it lower my amp draw?

    I can't see both compressors being gone?
    You probably meant RLA? You did not mention 2 things that may help, ambient and load.
    Officially, Down for the count

    YOU HAVE TO GET OFF YOUR ASS TO GET ON YOUR FEET

    I know enough to know, I don't know enough
    Liberalism-Ideas so good they mandate them

  11. #11
    Join Date
    Aug 2012
    Location
    willowick ,oh
    Posts
    261
    i will go out on the chopping block and say you need new compressor. very low compression ratio and low super. Unless someone drilled out the orfices.When you blocked up the condenser section i bet the suction climbed right up with the head pressure didnt it.

  12. #12
    Join Date
    Jul 2013
    Posts
    13
    Quote Originally Posted by heresjohnnyb View Post
    i will go out on the chopping block and say you need new compressor. very low compression ratio and low super. Unless someone drilled out the orfices.When you blocked up the condenser section i bet the suction climbed right up with the head pressure didnt it.
    No. The suction stayed roughly the same.

    With locked condenser(both stages reacted the same)
    Suction - 95psi
    Head pressure - 300psi

  13. #13
    Join Date
    Feb 2011
    Location
    Sacramento, CA
    Posts
    147
    In your original message you said your head pressure was 180, now it's 300? What is your sub cooling? I almost bet that it's high. What's the OSA temp?
    Last edited by GoColts; 07-30-2013 at 01:28 PM. Reason: Spelling

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