Cadillac Repair: A/C Conversion, r 134 freon, oil viscosity

Question
I need to know the oil viscosity and # of oz. required for the new 134a charge and any other recommendations for the conversion on my 90 Deville Coupe (do i have to remove the compressor and drain the old oil or ???).

Thank you,

Jim U.

Answer
You CANNOT convert a 1990 Cadillac R-12 system to an R-134 system due to the fact that the LOW PRESSURE sensor is NOT calibrated for R-134 freon and if you try and convert the system you will get an inoperative AC system and a CHECK ENGINE light on the dash which is caused by the low pressure switch not being calibrated for R-134 freon.

To date, There is NO fix or different sensor that can be installed to resolve this problem.

I get 2 to 3 questions every week addressing this conversion.