Over the weekend I converted my R12 AC in my 1991 745T to R134A strictly following the “Volvo Service Bulletin 200 ‘ Converting of A/C system from R12 to R134a’”. After filling the system with a little less than 1000g. The system runs perfectly with the vents blowing good cold air. However, after about 20 minutes of flawless running, it suddenly stopped. The compressor is cut off. The fill port where I still have the gauge and 1 lb bottle attached shows super high pressure (needle in the top of the red region, the gauge is the one came with a R134a purchase. So, it’s a cheap one). I immediately start bleeding the system from the extra R12 test port on the dryer and brought the pressure back to the safe range. However, the compressor will not kick on anymore.

I talked to a friend who knows about automotive AC and he concluded that the most likely cause is excess oil in the system. After the “retrofitting” the system has 200ml of fresh ester oil which I filled into the inlet of the new dryer plus whatever amount of R12 oil in the compressor (page 15 “Fill accumulator with ester oil (200ml) on the inlet side. Replug accumulator. Note: If compressor was replaced in previous step, no ester oil is needed for the accumulator.”). On the same page, if compressor needs replacing, drain the oil inside and fill it with 200ml of new ester oil. There is no mentioning of draining the old oil in the compressor if you’re not planning to replace it.

After talking to him I went back under the car and found the drain plug (17 mm?) on the bottom of the rear plate of the compressor where the in and out (low and high) tubings are connected to. I cracked open the plug just enough to let the bubbly oil out. After about 5 minutes and about 30 ml of oil drained, gas start to come out. I then started the engine, slowly started to fill the system. As soon as about 2/3 of a can (1 lb can) went in, the compressor started to run and the system started to blow cold air. I then, shut down the engine, thinking that everything is well now. This morning, I started the car to bring my daughter to the summer school. The air from the vent is definitely not cold while driving to school. Immediately after I came back home (~10 minutes) I hook up the cheap gauge to the fill port, there it is again, very high low end pressure! Thanks for reading and offering your advice. Erwin