The long version:
The mineral oil used in R-12 systems is not compatible with R-134a - it gels. R-134a requires a higher pressure drop to give the same cooling performance. Older dessicant is not compatible with R-134a. The solutions to these 3 concerns are:
1) Disassemble the system, pour flush into each component (except the accumulator/dryer) $16/bottle, & blow out all the old oil with compressed air.
2) Install a new orifice tube sized for R-134a and reset the low-pressure switch to 22psi.
3) Install a new accumulator/dryer with compatible dessicant.
4) Pour about 1/2 the recommended oil charge into the compressor & 1/2 into the acc/drier.
To ID the system as R-134a, change the port fittings to the new style. Adding a high-pressure switch set to ~500psi on the outlet of the compressor is also recommended.
Immediately after installing the new acc/dryer, tighten all fittings & evacuate the system. This removes air & water & tests for leaks. Start the engine, turn the A/C on HI fan, Max/Recirculate, Cold. It should not run because of the low-pressure switch. Install gauges to both ports & add refrigerant until the high side is about 450psi. The low side should be about 26psi, depending on the ambient air temp. Check for leaks.
The short version:
Buy the Intermatic kit at Wal-Mart for $35 and follow the instructions./wwwthreads_images/icons/smile.gif
Steve 83 Bronco 4.9L
Build it; Don't buy it...