I've been fiddling with my AC for a while, and finally have it where it's working good so figured I'd add my $0.02.
If you're getting a kit that come with the condenser, then all good. But my truck '92, was converted to r134a, and still uses the original condenser and works just fine. The PO did the conversion and didn't change the accumulator, so I was battling the black death. It was really nice to be able to flush out that condenser core. You may want to keep your old one around as a spare. I'd also recommend flushing anything you don't plan to replace, including hoses. You can rent an AC flush tool that hooks up to an air compressor from most autoparts stores, and using denatured alcohol (alcohol fuel) is fine. No needed to get the expensive AC flush stuff.
What made the biggest difference for me after actually getting the system running was to do the heater core bypass mod. Super simple and well worth it.
https://www.oilburners.net/articles/coolbypass.html
A few other things to note:
I found the blue orifice tube worked best for me here in the southeast. The red tube worked better at idle, but not as good while cruising. I tried one of the variable tubes, and it worked great for about 15 minutes, till it got clogged. Obviously, I was dealing with some system continuation, but I still wouldn't trust them. When I pulled it, seemed clean. So I decided not to flush the system again. Installed a blue tube, pulled a vacuum, and charged. Been working just fine since.
Make sure your air box in the engine compartment is well sealed. Any leaks mean you are dumping conditioned air outside of the cab. I used some electricians duct seal around the seams before assembly to make sure I had a good seal. Some weather stripping would probably also work.
Folks claim good improvements from insulating the air box as well. You can get a product from your local hardware store HVAC section that has like a half inch of adhesive foam insulation bonded to foil. That would probably be the best thing to use. But I just covered my air box with some foil duct sealing tape that I already had to act as a radiant barrier, and that seems to work pretty good.
You may also want to get some foam or rubber pipe insulation and use it on the low pressure return line from the evaporator to the compressor. This won't really help with performance, but with that line traveling right over top of a hot engine, it is cheap insurance for the compressor to make sure the coolant stays gaseous as it enters the compressor.
Make sure your vacuum pump is working correctly and that you don't have any vacuum leaks. Both the blend doors work off of vacuum switches, so low vacuum or a leak means you'll be pulling outside air and/or pushing conditioned air through the heater core.
When you have your air box open to get at the evaporator core, I'd recommend hooking up a vacuum pump (a hand pump is fine) and testing the blend door that operates the heat/cooling mix. You can see it just at the back of the evaporator box towards the firewall. It may need to have new foam seals, or you may need to replace or adjust the switch.
This would also be a good time to inspect your blower fan. These trucks don't have cabin air filters, so it may have pulled in some junk over the years. I had to remove about a rats nest and a half from mine.
Finally, I'd recommend adding a high pressure switch in line with the low pressure switch to the compressor. I believe this is how the factory AC is setup from late '93 onward. If you ever have a problem like a clog causing high pressure, it'll stop the compressor until the pressure drops. You should notice the compressor cycling, or poor performance and hopefully be able to fix it and keep from damaging the system or popping the relief valve and dumping all your refrigerant. Just ask the autoparts store for a high pressure cutoff switch from a '94 and wire that in. I screwed it straight to the high pressure fill port after charging, but you could also tee it off if you wanted. See:
https://www.oilburners.net/threads/high-pressure-cutout-switch.83043/
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