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Freon capacity for 1988 Peterbilt 379

Discussion in 'Heavy Duty Diesel Truck Mechanics Forum' started by Vgarza32, Mar 11, 2023.

  1. Mar 11, 2023 #1
    Vgarza32

    Vgarza32 Bobtail Member

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    Needing the Freon capacity for a 1988 Peterbilt 379 with flat top sleeper. Has 4mg b model cat. Trying to dial the ac system in. Any help would be greatly appreciated. I’m figuring around 4lbs but wanting to know an exact number that it calls for. Peterbilt is being as worthless as tit on a boar at the moment.
     
    Vgarza32, Mar 11, 2023
    Vgarza32, Mar 11, 2023
    #1
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  3. Mar 11, 2023 #2
    pushbroom

    pushbroom Road Train Member

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    chrome_X2qtGkNSC6.jpg
     
    pushbroom, Mar 11, 2023
    pushbroom, Mar 11, 2023
    #2
    Rideandrepair Thanks this.
  4. Mar 11, 2023 #3
    BoxCarKidd

    BoxCarKidd Road Train Member

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    There is no exact amount of R134A for a R12 system. Suggest starting with 75% of the R12 amount. Open both doors, set on fresh air, make engine fan and compressor run continues, engine RPM at 1200 or so. Put a thermometer in the dash air discharge. Add freon at about 4 OZ or 20 PSI increase on high side and let stabilize. Keep adding freon until the temperature no longer drops and you are done.
    That takes a little time but 4 OZ can amount to 10 degrees in some of those 134 conversions.
     
    BoxCarKidd, Mar 11, 2023
    BoxCarKidd, Mar 11, 2023
    #3
    Rideandrepair Thanks this.
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