Automotive Air Conditioning Information Forum

It has r134a fittings so I assume it was converted at some point but there are no labels indicating that. Car may have been sitting for years and has less than 10 psi now. Got it on a vacuum pump now and will check if it holds. If so, how much R134a to recharge? Here is the original R12 label, it's the 4 CYL.

Generally speaking, a conversion from R-12 to R-134a usually takes approximately 75 to 85-percent of the original R-12 charge, which according to the under-hood decal on this car is 46.4 ounces net weight.

Start at 75-percent of the original charge, or about 35 ounces, and slowly work your way up, adding a couple ounces at a time until the center dash vent temperatures drop, level off, and just begin rising. Stop adding refrigerant at that point, and the system should be optimally charged or very nearly so.

We don't know what was done to the system before you got it but presume that all the old mineral oil was properly removed, that the correct amount of PAG oil was added, and that the R/D was changed-out to one having desiccant that is compatible with R-134a.

The refrigerant obviously leaked out, though. So look around for any oily spots, including on the lines, joints, front of the compressor, and the condenser. Oily spots usually indicate a point (or points) of refrigerant leakage.

Speaking of the condenser, check to see whether it was changed to the more efficient parallel-flow type, which will give us another clue that the system was converted.

hi
R12 AT 220PSI = 145f
R134A AT 245PSI = 145f

evacuate /vacuum test
charge till 80% by weight ,then try to get upto 100% not exceeding 245 psi . Over 230 is considered fairly high .
look for compressor flooding ie suction getting very cold freezing ,this is real bad
good vent temp
subcool , [ going out of condenser ]
If its a txva low side around 22--35psi operation is great
sight glass minimum bubbles after running for a few minutes