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  1. #1
    Join Date
    Mar 2012
    Location
    Raleigh, NC
    Posts
    34

    Low pressure on high side

    I have two three ton carrier units, (they're neighbors), anyway, one unit has low pressure on the high side, about 100 psig. The other unit has real high pressure on the high side, about 300 psig, but its only 75 degrees outside. Both carrier units and neither are heat pumps. Any ideas?

  2. #2
    Join Date
    Mar 2012
    Location
    Raleigh, NC
    Posts
    34
    And to add, the suction on the unit with the low high side pressure is high, about 100 psig. And the suction on the unit with the high pressure high side is normal and super heat is correct but the subcooling is way off

  3. #3
    Let's start with the low-high side unit...
    What is your superheat and sub cooling?
    Are your line temps the same (within a couple degrees of each other)?
    Is your compressor actually running (pulling amps)?

    I've found many compressors that have symptoms similar to this, where the pressures are close, amp draw is half of fla, and the line temps are the same...the cause of this is usually a mechanical failure within the compressor.

  4. #4
    Join Date
    Dec 2002
    Location
    SouthEast NC ICW & Piedmont Foothills
    Posts
    7,635
    start by giving the actual pressures instead of high/low observations

    that one machine isn't pumping or your gauges are on correctly
    It`s better to be silent and thought the fool; than speak and remove all doubt.

  5. #5
    On the unit with the 300 psi head;
    What is your superheat and sub cooling?

  6. #6
    Join Date
    Feb 2010
    Location
    In a boiler room
    Posts
    7,119
    Cool Change, are you in this industry as a tech? Or is this DIY? There is nothing in your profile and in this and the other thread you couldn't answer the most basic questions such as Superheat and Subcooling.

    We are curious....

  7. #7
    Join Date
    Apr 2001
    Location
    Western PA
    Posts
    1,801
    Maybe we could have a sticky about posting actual temperatures and pressures when asking for refrigeration advise?

    I can see why people give us such incomplete data. If they had collected all the pertinent information, they probably wouldn't need to ask us our diagnosis! With Superheat, subcooling, temperature outside, in return, and supply, we can pretty much figure it out. If we really want to dig deep, give us model and serial,static pressure, wet bulb in and out, flux capacitance, amps, gigawatts... How about the customer's actual complaint once in a while?

    Maybe as part of the registration process, they can sign and notarize a pledge to give us some more information!!!

    Add some gas and report back.
    Jason

  8. #8
    Join Date
    Mar 2012
    Location
    Raleigh, NC
    Posts
    34
    I am a beginner tech in the industry. got a universal with verrrry little experience, so if u wanna work with me I appreciate it. if not, thanks anyway. I left the job and do not remember the data but you bet I will write it all down to report next time.

  9. #9
    Join Date
    Nov 2011
    Location
    USA
    Posts
    385
    Quote Originally Posted by Cool Change View Post
    And to add, the suction on the unit with the low high side pressure is high, about 100 psig. And the suction on the unit with the high pressure high side is normal and super heat is correct but the subcooling is way off
    The compressor's not running on the 100 psi low/100 psi high unit and the other is probably overcharged.

  10. #10
    Join Date
    Feb 2010
    Location
    In a boiler room
    Posts
    7,119
    Quote Originally Posted by Cool Change View Post
    I am a beginner tech in the industry. got a universal with verrrry little experience, so if u wanna work with me I appreciate it. if not, thanks anyway. I left the job and do not remember the data but you bet I will write it all down to report next time.
    Thank you! Welcome here! We don't really like to give out DIY info. It helps to fill in your profile.

    On the unit with equal pressures it sounds like the compressor is not pumping, check amp draw to common winding.

    Have you applied for pro membership yet? You need to have 15 posts. All the good tech info is is over in the pro forums. See the bottom of my post for the how to.

  11. #11
    Join Date
    Mar 2007
    Location
    NW AR
    Posts
    2,478
    DIY tips or answers do leak out but usually only when the right questions are asked. No offense at all, we all started somewhere and are still learning, but sounds like you just have some gauges and an epa card.

  12. #12
    Join Date
    Mar 2012
    Location
    Raleigh, NC
    Posts
    34
    So lets start with the unit I'm on right now. I have a superheat of 70 degrees, 30 pounds suction pressure. Head pressure is 155 with -5 degrees subcool. Im drawing 6.7 amps on the compressor. I added two pounds of r22 which brought the stats up to what I am reporting them currently but am reluctant to add more freon till I get some input. T 3.5 ton unithis is a heat pump on a goodman

  13. #13
    Join Date
    Mar 2012
    Location
    Raleigh, NC
    Posts
    34
    On the one with low high pressure I chalked it up to compressor going out. I went there to do a prevent maint and found the condensor 1/4 buried in the dirt. Told the homeowner they needed a new compressor very shortly. hope I was right. and think I am but will check the amp draw to the common as suggested. It was drawing 11.4 amps

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