A/C temp

When converting to R134, you should only fill the system to about 80% of the original R12 capacity. Hight side pressure should be about 2.2 times the air temperature in front of the condensor. As the outside humidity rises, the high side can be increased to about 2.5 times the temperature.

Another helpful thing is to hold the engine speed at your normal highway cruising rpm, 3000 rpm for 4cyl, about 2500 rpm for 6 cyl and some where near 2000 rpm for a v-8. at these speeds, check to see if the compressor short cycles (A/C fan on high, windows open, with warm outside air). If it does, you can add freon until the compressor stays on. Low side will be 20-30psi, high side at the 2.2 to 2.5 times the outside air temp in front of the condensor. Do not use the rpm method on a cool or cold day, like 60 degrees or less. At the lower temps, the A/C will short cycle due to the cooler air blowing across the evaporator.