Hi Fred,
You have gotten really solid advice on here. Always replace the drier any time the system is opened up. If you think there is contamination or the refrigerant has a burnt smell you want to flush the system. Absolutely nitrogen charge, carefully so you don't blow one of the rubber lines (voice of experience) ha and while you have it charged with nitrogen, soap bubble all fittings. best to leave it charged over night and check your pressures again to be sure you don't have a leak. You will have a slight variation due to temperature change. Evacuate and recharge according manufacturer specs. I don't know if the manufacturers weigh in the charge when having that long of a lineset to the front. If they do then weigh in the correct amount. Also as said before don't waste your money on small cans and find someone with an epa license to hook you up a jug of 134A. Yes, I do HVAC and have a slight idea about this.... slight... as I get older I find I know less than I thought I did.
This another thought I had after reading all the posts. I not trying to hijack the thread and if out of line I' sorry, still kinda new here. With the AC being driven off the engine with a hundred feet of hose, has anybody ever thought of using a compressor like the ones for the back of suburbans to run the dash air? Just a thought. No long line sets, less refrigerant, not engine driven so if it seizes it won't burn a belt off. Again, If i was out of line here I won't be offended if it gets deleted.
Good luck on your AC