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Thread: Top off Truck

  1. #1
    Join Date
    Dec 2003
    Posts
    144

    Top off Truck

    Need to top off my truck w/ 134a. I'm not sure how to do this. My first thought is to monitor superheat due to a fixed orifice MD. Is this right? I don't want to recover/evacuate due to a leaking evap core (which i will replace next year), I don't want to pull any moisture or non-condensables into the system.
    Still learning....

  2. #2
    Join Date
    Oct 2004
    Location
    Central WA
    Posts
    1,306
    Yeah, superheat & check for some subcooling while you are at it. Most important is put a brick on the gas pedal and try to hold steady at about 1800 rpm. Open all of the vents, put the fan on high, and set the a/c to "max" or "recirculate." Don't worry too much as there is usually an accumulator in the system, but obviously don't go over the nameplate charge.

    Your split will be high as automotive systems have huge capacity - usually 3 to 5 ton - with a very little fan...

  3. #3
    Join Date
    Jul 2008
    Location
    Denver, CO
    Posts
    4,203
    I always jump out the pressure switch to keep the compressor running and shoot for a 13 superheat reading on a fixed orfice, if it has at TXV I shoot for a beer can cold suction line.

  4. #4
    Join Date
    Aug 2007
    Location
    Winter Haven, FL
    Posts
    3,584
    None of these methods are proper. Evacuate the system and weigh in the charge

  5. #5
    Join Date
    Oct 2004
    Location
    Central WA
    Posts
    1,306
    Quote Originally Posted by Joe Harper View Post
    None of these methods are proper. Evacuate the system and weigh in the charge
    Kind of hard to do with a leak that you are not ready to fix. 15 minutes to get you by with some cold a/c, or 1/2 to a full day ripping out a dash to replace an evaporator...

    Or he could take it to an ASE and 609 certified professional (proper thing to do). Then that guy can dump a pound in and call it good...

  6. #6
    Join Date
    Jun 2005
    Location
    Winston-Salem NC
    Posts
    1,133
    Quote Originally Posted by cjpwalker View Post
    Kind of hard to do with a leak that you are not ready to fix. 15 minutes to get you by with some cold a/c, or 1/2 to a full day ripping out a dash to replace an evaporator...

    Or he could take it to an ASE and 609 certified professional (proper thing to do). Then that guy can dump a pound in and call it good...
    /agree

  7. #7
    Join Date
    Jun 2010
    Location
    Tampa, FL
    Posts
    101
    If you're sure the leak is in the evap. Try a small can with sealant in it from the auto parts store. Maybe you won't have to pull the dash.

  8. #8
    dump in one of those small cans. if the accumulator and suction like are cold while it is running, stop. If it ain't cold, add another can.
    Hey cockroach, don't bug me!

    www.AskTheDiceman.com

    www.TheColdConspiracy.com

    www.Pennwood-HVAC.Com

    Bring Em Home....

  9. #9
    Join Date
    Mar 2010
    Location
    Kent, WA.
    Posts
    183
    ive seen r134 cans at the auto parts store with the hose and a gauge. the instructions were to turn on a/c on high and fill till the needle is in the middle of the green area. now that's scientific.

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