I have a 69 Cutlass with factory air and just changed the evap coil and would like to know how much R134 it will need. I had it charged in the past but they just took an experienced guess. It worked great.........for a week. I looked in the CSM but it is for R12.
thanks,
Steve

 

I’d use R12

 

R134 should be charged based on pressure not weight or volume like R12. Get a set of gauges and do it right.

 

Agree with the above. I think a “general” approximation is 75% of the R12 charge weight. But gauge pressure is the only way to be certain.

 

R134 will work in the factory R12 A/C system but there are a few things that need to be adjusted/updated for it to work right. The compressor oil needs to be changed, the o-rings should be updated to silicon instead of the original rubber, and the system should be purged and cleaned at a minimum. The R134 refrigerant has much higher operating pressures than the R12 as well. When I was installing A/C systems in Phoenix, we used a temperature vs. pressure chart to get the system charge correct. R134 is much less forgiving than R12 because the pressure can skyrocket quickly if the condenser does not have enough air moving through it. Even a cheap set of gauges from Harbor Freight, Amazon, or Ebay is an absolute "must have" item for charging a system that was not originally built for R134.