sneakingfart
OBS Enthusiast
Since the system is empty, I agree with just replacing the valves. They are cheap. Do both the low and high pressure side. If I recall correctly, the high pressure side is not the regular bike valve like the low pressure side, but you can buy it on RockAuto for around $10. But I am going to bet that is not your problem.The parts store had a little bitty screwdriver tool to remove the valves but it looked just like the tool I had at home to remove bike tube valves. I have some new valves so I'll see if I can swap them out and clean good after. It would seem to make sense to do that before adding dye since the system is empty now.
If this was my truck, I would replace the condenser and compressor right off the bat, especially if your compressor is original (and 29 years old). Do the orifice tube as well, it's like $3 and very easy to replace. The condenser is very easy as well, you just have to remove the grille. Replace every o-ring that is easily accessible. Ideally all of them, but some are hard to reach. Just buy an AC o-ring assortment on Amazon, and some Nylog lube. The manifold that connects to the AC compressor uses copper crush washers, replace those as well, don't reuse them like I tried (and failed) to do. I also replaced the low pressure and high pressure switches, and o-rings. I did confirm a leak at the condenser using dye, and my compressor was oily. No leaks so far, about 6 months in.