heating and cooling

I have a question about converting an r 12 ac system to an updated to an r 134 system. I have a 1990 cherokee with the 4.0 inline 6. what all do i need to do it. Is there anything i need to modify to make the system work.

thanks

Buy a kit, follow the instructions.

Here is a basic explanation: http://searchwarp.com/swa15436.htm

keep in mind that you will want to have the system purged of it's R12 AND the mineral oil that was used with the old refrigerant. R134a will not carry the mineral oil so you will need to add Ester oil (best for retrofits) to lubricate the compressor.

that explanation fails to address oils in any manor, but if you get a "kit" designed for retrofit the refrigerant may or may not have any oil in the cans. Do your homework on quantities required for your application and the pressure you charge to (based on ambient air temperature) and good luck with the retrofit.

I'm in the same boat there and I want to do all the work myself, except for evacuating the R-12. I don't know if there IS ant R-12 left in the system but once they've evacuated the system can/should I go about flushing the system.

...or would the "kit" explain all that?

I did the kit thing several years ago. didn't even evacuate the sytem or change the oil. It kind of worked, not as cold.
Just replaced the compressor with an identical used one. I drained all the oil out that I could over several days. hooked everything up. Evacuated using one of those cheep HF vacuum devices that uses compressed air. Checked using HF gauges for leaks by taking the system down to 30" Hg. Checked 24 hours later and it was still at 30" Hg. Added ester oil as it is compatable with R12 and 134A and will work with the remaining mineral oil. Added the 134A per limits recommended using the gauges.
Works great.

I did the same for my WJ when I had to replace the blend doors except I didn't need to add oil. Had to disconnect the evaporator in the process.