This Sanden unit, how does it compare to the R4 unit? Can it run R12? I modified the TBI's A/C bracket to mount to the LM7, can the same be done for the Sanden?
D'oh! My apologies, I thought you had the Vortec style accessories. So far as I know, the only replacement for an R4 is an R4, so scratch the Sanden suggestion. As far as R12 goes, if your truck is a '95 it should have been 134a from the factory, as I'm fairly certain that '94 was the last year for factory R12 AC systems in production cars. Could be some grey area there, but that's what I recall.
I would suggest replacing the condenser with a parallel flow unit, flushing all the lines, and replacing the orifice tube. Flush the evap core as well. If you have rear air, you will have to disassemble the rear AC box to replace the expansion valve and flush the rear evaporator. If your compressor had an internal failure (as opposed to just leaking) disassembly of the rear system and thoroughly flushing everything are mandatory, as debris is generally spread throughout the system during the run down to complete failure. Clean the outside of both evaporators to maximize heat transfer, airflow, and cooling efficiency.
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This is what my evaporator looked like prior to cleaning. Nineteen years of dirt, leaves, mold, and hair. It made the air several degrees colder and smelled better to boot! If you have never cleaned yours, you can bet it looks much the same.
Be sure to use the proper oil for whatever refrigerant you use. PAG 150 for R134a systems and Ester oil for R12. Once all is said and done, pull a vacuum on the system for a minimum of 2 hours, and verify that it holds said vacuum for at least 15 minutes. Longer is better, as some leaks can be very small under vacuum but very large under pressure. If you have access to a vacuum pump with micron gauge, a sub 1000 micron vacuum would be great for a mobile AC system, but below 2000 would be nothing to sneeze at. Charge the system by weight, not pressure, especially if using R134a. R12 is much more forgiving of improper charge, which is one reason people had much better "luck" using it (especially DIY) than 134a. If you don't have good scales and a good vacuum pump, take it to a shop and have them pull the vacuum and charge the system. Too much money and time invested to mess it all up with a dirty system or improper charge.
And please, please, do not convert it to R12. If you do everything I mentioned, you will get good performance out of the system, and won't pay through the nose for refrigerant.