Here's my experience with the systems in theses trucks. When I bought my 84 the compressor had no belt on it but was loose. So I pulled a vacuum on it for 45min, I had oil coming out of the evacuator, which told me the system was oil logged. Figured there was alot of oil left in it, so I added none and charged with 134a.
3yrs later headgaskets required the removal of the condensor, so recharge after adding 3oz of ester oil.
3yrs after that (2 weeks ago) compressor failure, got a used compressor, disassembled the old one to find out why it failed. Piston cracked and jammed the metal ball and disk that rides on the swashplate into the next piston and seized the compressor. Left system alone no parts or metal left the compressor. Installed new compressor, evacuated for 90min, charged the next morning. Starting off at 20''hg I added about 38oz, low side was 36psi and high side was around 130. Vent temps hold a steady 33 degrees.
New Orifice tube. - If you have the blue tube factory, go to a red, if you have a red tube factory, go to an orange. If you live in a more extreme climate, I would go with Variable Orifice Valve. There are two by temp range
I am in the process of replacing my entire A/C system. My old orifice tube is blue. What is the purpose of switching to a red orifice tube? And where do I get a red one?
The store will have the red ones as well as the blue ones. The orifice tube sets the flow and pressure of the system as it runs. The different gases run more efficiently at different pressures and flow rates. That's about all I know. Yours will run ok with the blue one, it might run even better with the red one. I know the 96 powerstroke system I just worked on had a red valve and it came from the factory with r134a. I believe they also put a larger condensing coil in front of the radiator for the r134a. But these are just tweaks to the system to get it running the best on the different gas.
Dave, FWIW, Ford changed to R134a in 1994. When they did this they changed the condenser to a multipass and the evaporator core was increased in size. The orifice tubes are basically sized originally for the area to be cooled. Archion has the chart somewhere, but I think it was orange, blue, red in order of increasing size. I used a red when I first converted mine. I now have a complete 1996 system installed. Big improvement on it, insulated AC box. Before, if I stopped in hot weather it would take 20 min or more for the air to get cool again, now it's more like 2 min.
One other thing, and I don't know if it was other engines, but the 460 got a smaller compressor pulley (spins faster) starting in 1996.