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  1. #1
    Join Date
    Aug 2004
    Location
    Texas
    Posts
    88
    hello gentlemen, this past friday I was on a no ac call, head psi was 350 and rising, suction was 75. This is a 2 ton, with a slant coil, at an apartment complex. Capillary tube. The unit will not pump down. Begins but bypasses. Ok. I recovered the refrigerant. Blew dry nit. through. First making sure the liquid dryer wasn't in the loop. I put a lot of pressure through to the evap. coil but barely any coming back no matter which direction I blow into. I am saying restricted coil or cap tube. ?????????

  2. #2
    Join Date
    Mar 2005
    Location
    Suppy NC
    Posts
    4,513
    sounds like you got it
    time for a new coil and clean the condenser coil to

  3. #3
    Join Date
    Aug 2004
    Location
    Texas
    Posts
    88
    well, my boss says since it has a cap tube I won't get much pressure coming out. He says that blowing nit through doesn't prove it is restricted because it is a cap tube. But I think he is wrong. So I left it for him. HE put a new condernsor on , and pulled a vacuum. And left the evap. coil in. HE called me this evening and said he has a high head on the new condensor. 315psi. and told me he was going to put a new evap coil in. But not because it is restricted but because it has contaminets in it. What I want to know is this...does a cap tube really choke the air down that much that when you put about 300 psi on it it only barely exits? I am still thinking restriction, but he tells me is has certifications out the rear.

  4. #4
    Join Date
    Mar 2005
    Location
    burlington county n.j.
    Posts
    9,699
    a lot of cap tube coils had a strainer screen in the distributer right before tubes. used to cut open and install coupling after digging out screen, then install drier in liquid line. coils made that way are to the age now we just replace them.

  5. #5
    Join Date
    Aug 2004
    Location
    Texas
    Posts
    88
    screens could get dirty then...
    boss says you can disconnect the fan motor and run the ac..then watch the cap tubes. If one begins to frost before the others it is restricted...does this sound true?

  6. #6
    Join Date
    Feb 2005
    Location
    Dothan, Al
    Posts
    3,453

    Don't understand

    With 350 head pressure, why are you looking for a restriction ? Restrictions will not ( I repeat, NOT ) cause high pressures.....
    High pressures due to possible overcharge trying to overcome a restriction.
    How much refrigerant did you recover ? Was it more than nameplate?

  7. #7
    Join Date
    Dec 2002
    Location
    Houston,Tx.
    Posts
    15,819

    Re: Don't understand

    Originally posted by bornriding
    With 350 head pressure, why are you looking for a restriction ? Restrictions will not ( I repeat, NOT ) cause high pressures.....
    So if I go out to my unit and crimp off the liquid line 75% the head will stay the same.
    __________________________________________________ _______________________
    “Experience is a hard teacher because she gives the test first, the lesson afterwards". - Vernon Law

    "Never let success go to your head, and never let failure go to your heart". - Unknown

  8. #8
    Join Date
    Feb 2005
    Location
    Dothan, Al
    Posts
    3,453

    Mr. Billpro

    Yur head pressure would go down as would yur suction pressure

  9. #9
    Join Date
    Apr 2004
    Posts
    7,680
    He's right bill, sorry, its just like pumping a unit down.

    That said, if the line set is long requiring additional charge, while pumping the unit down you may indeed get to the point where the condenser is completely flooded and you could blow the internal relief. Remember, you are reading liquid from the line side of the LL valve and have no clue what the discharge pressure is.

    I'm not sure I have a real beef with the pressures other than the head is high, I am guessing someone checked the outdoor coil, verified the outdoor fan and didnt jack the system with too much refrigerant. Of course we dont know the outdoor ambient.

    My guess, based on the OP description is the suction was low, someone decided to add refrigerant to get it up and now its overcharged. Airflow, or load was probably never considered and that is why the suction was low in the first place.

  10. #10
    Join Date
    Aug 2004
    Location
    Texas
    Posts
    88
    ok doc.. I see your point.. when you pump down the high side gauge will follow the suction line gauge because,well their is no refrigerant left in the lines and down it goes. But I am a little confused here. Lets say the evap. is 80 even 90% clogged. The compressor sucks what freon it can which would cause a lower suction pressure, now the liquid is pushing into condensor and collecting behind the restriction, wouldn't it make since that the discharge psi would go up? If my arteries start clogging up I get high blood pressure. I don't know?

  11. #11
    Join Date
    Dec 2002
    Location
    Houston,Tx.
    Posts
    15,819
    Also why is it that we had a Goodman unit about two weeks ago with a head of 375 and we found that the liquid line drier was full of crap that come from the piece of junk strainer drier they install from the mfg. and when we took out both driers and installed a new liquid line drier the high side went down to 260 I am clueless.
    __________________________________________________ _______________________
    “Experience is a hard teacher because she gives the test first, the lesson afterwards". - Vernon Law

    "Never let success go to your head, and never let failure go to your heart". - Unknown

  12. #12
    Join Date
    Mar 2005
    Location
    Suppy NC
    Posts
    4,513
    is the new unit a scrol? i have been told that a scroll will not match up well with the old cap tude coils and in trying to do so you will wind up with high head and low suction from over chargeing the unit best to replace the coil and be done with it

  13. #13
    Join Date
    Aug 2004
    Location
    Texas
    Posts
    88
    well this really wasn't my baby to work on. I suggested they put a new condensor in and match it with new coil. WE had a spare in storage. Just to get us out of a jam. Way behind. These units are 2 ton Goodman 10 seer. Another tech installed the condensor and pulled a vacuum on the system. He suspected non-condensibles. We understand that the guys who used to work here didn't pull vacuums and reused the liquid dryers. Go figure. I am chalking this up as a learning curve.

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