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problem with ac pump?

reggofcal on Wed July 09, 2008 4:08 PM User is offline

Year: 88
Make: frieghtliner
Engine Size: 365
Refrigerant Type: 134a
Ambient Temp: 100
Pressure Low: 2
Pressure High: 148
Country of Origin: United States

I charged the ac and the clutch engaged but my high side is 148 low side is 2. I only put two 12oz cans of freon. I dont know if more freon will raise the low side or do I have a bad compressor.Also when I turn the truck off the pressures equalize around more question if you over charge the system will it make the clutch kick in and out around 1 minute intervals and what are the correct readings low side 30 highside 250? any help will be greatly appreciated

mk378 on Wed July 09, 2008 4:48 PM User is offline

Likely you need more, quite a bit more. Systems were rather large back in those days. Can you find the manufacturer's specified charge on a label anywhere? Compressor seems OK because it is pulling the low side down. Is this system properly converted? Did you evacuate the system before charging? High side 250 is a good number on a 100 degree day. When severely overcharged the high side will go up to 350 or more and then the overpressure switch will start turning the compressor on and off.

To avoid confusion you should rig the radiator/condenser fan so it runs all the time while you're charging. On big trucks with an air-operated fan clutch that can usually be done by disconnecting the wire to the air valve.

Chick on Wed July 09, 2008 8:07 PM User is offlineView users profile

Here is a vac/charge procedure to use as a guide. As stated, those systems used a "few" pounds of refrigerant, so you'll be using around 80 to 90% of the R12 charge, try to find the system capacity, if not charge it until you get a high side around 2.2 times ambient temp on the high side, then slowly charge until the suction line is cold to the compressor. Inlet and outlet of the evap should be the same temp, outlet (suction line) a little colder is fine.. Hope this helps.

Email: Chick


Freedoms just another word for nothing left to lose

reggofcal on Thu July 10, 2008 12:28 AM User is offline

I got the high side to 250 but the low side never came up, its still at 2. I put about 6-12oz cans. what problems would be possible at this point. how do I check for them.high side line was hot and the low side was not as hot but was not cold. any info will be greatly appreciated thanks.

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