Hi y'all, just signed up to your great site. I'm troubleshooting a '90 F-150 XLT Lariat A/C system. I'm sure the R12 charge is long gone---no gas exhausted from depressing Schrader valve(s) and the compressor clutch will not activate (low pressure cut-out switch)---fuse is good. I plan on evacuating the system, checking leakdown and charging w/ a 134a kit, then testing for leaks. I have access to an electronic leak detector.
My question is: Should I replace the o-rings and compressor seal now while the system is empty before charging and leak testing? I'm thinking I could save some time and 134a by replacing these items now.....BUT....this truck is old and has had a lot of corrosion problems (NE winters) and I'd hate to ruin the tubing or nut if by chance they're frozen. These parts are pretty cheap and common sense tells me to do it now, but I had to wonder if others here on site have had experience on this issue. Can compressor seals and o-rings possibly live this long? Any advice or opinions would be highly appreciated. Thanks, Fast Ed

 

I'd replace the accumulator and orifice tube, install conversion fittings, flush the evaporator and condenser, charge it up and add dye before trying to fix any leaks.