Originally Posted by KCM

In the past I've read on this forum of bad experiences switching to R-134, but from personal experience have had very good luck. I have converted two late eighties Fords, a Mercedes W123, and an aftermarket A/C kit. They have all been running for 3 to 4 summers with no problems. I changed the o-rings, pressure switch, and accumulator/drier in all, the compressor on one Ford and the Mercedes, and the expansion valve on the Mercedes. I used the recommended oil for R-12/R-134 compatibility and filled the system to approximately 85% of the R-12 charge.

One Ford is my sister's, and she claims it is just as cold as with R-12. I checked the Mercedes, and the air outlet temperature in the center vent was only a couple degrees higher than factory specs, and it can freeze you out most times. The only times it will not freeze you out is on extremely hot days, around 100, but still does a very good job of cooling. The aftermarket kit was pretty much a quicky job, but nothing has failed in the system yet.

The main reason to switch to R-134 is price, though it is getting high too for some reason. If they did it right, I don't know why you shouldn't leave it in there. Try it for a few days, and if you don't like it (which sounds like is the case already), have them switch it back. Just make sure you tell them this up front. They were probably just trying to do you a favor by switching, as the system was being repaired anyway. Plus you should have a warranty on parts and labor for a while. I bet they will charge you for the R-12 freon, or at least the difference in price.

One thing to check is that the auxilliary fan is working properly and is actually running. Had a service guy tell me once that cars with the electric fan take better to the retrofit than without. This most likely is due to cooling of the R-134 in the condenser as much as possible to increase efficiency.