Also, for flush, you can use mineral spirits. Real A/c flush cost more than
fine wiskey. Folks use  a funnel to pour it into stratigic areas of the a/c
system. Then work it back and forth with air pressure.  Then they blow it
out the other end.What a mess. I have a flush gun. Cost about $35. It is a
sig fuel bottle with a 3 ft line at the bottom, that attaches to a air
nozzel. The cap has a valve stem that will accept a air chuck for
pressurization. Fill it 3/4 with fine mineral spirits, and pump the
remaining 1/4 up to 110psi. Before you let this monster squirt gun loose,
attach a hose on the exit of the long a/c hose that you  are cleaning. Put
the other end in a 5 gallon bucket. When you finally pull the trigger(ask
the hose if it feels lucky), the cleaner rumbels down the hose scraping
anything in it's way. Kinda like that big ball that chased Indiana Jones.
When it gets to the end,it erupts into the bucket. And I do mean erupts.
110psi  is enough pressure to make clean the longest of Vanagon hoses. What
a mess! But it is contained. A very civilized way to go, and it is great
fun, too. One works their way through the Vanagon a/c circut, only removing
specific o-rings(leave well enough alone!). For example, I did the
evaperator inlet, to compressor parts as one. Another is the condensor
inlet, to the reciever dryer, as one. The reciever dryer gets cleaned(if
you are me,maybe) or replaced. The hose from the reciever  to the
evaperator gets done seperately. The long hose from the compressor to the
condenser inlet is the fun one. 20 feet of fun.

When clean, get a big two ounce syringe from southern states( used to
inject  cows), and put two oz of oil in the condenser inlet,1  in the
reciever dryer,two in the evaperator, and two in the remaining hoses. Be
aware that the refrigerant will blow the oil areound and distrubute it
evenly. Dont let it all go into the dryer.It wont leave too easily. I think
8 oz. go into the compressor fill hole. New green or whatever o-rings
allround for the opened hoses. Get a 134a expansion valve and test your
repair talent in tight places , by repalcing it without dropping the top
westy cabinet.

If  your compressor hasnt been used for a couple of years, it is bad. Our
saviors at bus depot will sell a new one for $300. What happens is the
shaft seal dosent get lubed , and it shrinks forever. The refrigerant then
leaks out pretty quickly ,sometmes.Get a new one.not rebuilt.

Thats mostly it. Charging is another story.