[68c10airstream]

Hi 68 fixeruper, The old rule of thumb is approximately the temp of the day plus 100psi. Example= 90 degree day plus 100= high side when compressor is engaged would equal 190psi. Also vintage air may have an inline sight glass, and the old rule of thumb is fill until sight glass bubbles just clear up and then 2-3 more ounces. This is memory recall as i was a dealer mechanic for 30 plus years and i have been out of the trade for a while. If member "clinebarger" gets on here he will be spot on, trannys and ac are his specialty, currently working in the field i suspect. Good luck, Brian Fuller