Jeep Repair: 99 Grand Cherokee a/c problem, pressure gauge, grand cherokee

Question
I purchased a 99 GC Limited about a year ago and am just now having a/c problems.
I put a pressure gauge on the low side to check if it need a refill, but here's the problem: The pressure reading starts at about 10 but then slowly moves up to 65 when the clutch disengages, it drops back to 10 and starts all over. TRhis cycle repeates itself every 8-10 seconds. My question is, how do I get an accurate reading if the system won't stay engages, and does anyone have an idea why this might be cycling so frequently? Any help is greatly apprecaited.

Thanks


Answer
Sounds like to me the system does not have enough freon to run.  When the compressor runs the low side pressure will drop, and the high side pressure rises, when the compressor stops the pressure is equalized on both sides.  The low side pressure should be about 30-40psi when the compressor is running (you may need to add more freon).  Before you charge an A/C system the system should be vacuumed, and charged exactly to specs or damage may occur to the system.  If you have the money to spare I would take it to a shop with a R-134 machine.  You also need to make sure there is adequate oil in the system.  Hope you get it fixed!