I have had my 91' 740 for 4 1/2 years and had to add R-12 for the first time from my stash I bought in the old days. I had to add because the pressure was too low to actuate the pressure switch on the receiver/dryer. My question is this: I added two 12 ounce cans and am wondering if I added about the right amount? I added the second can after the receiver dryer was just noticeably cooler. I am pleased with the operation, but know that the system can be hurt with too much R-12. Any guesses as to roughly how much should be added from not enough pressure to activate the switch to full? I took the car out for a ride and with the fan on full blast and all vents but the center one open and on recirculate, the temp was 38F. It was about 46F idling. The ambient was about 78F. Again, I'm very pleased about the operation but wonder if 24 ounces was too much R-12 to add. Thanks.