Air conditioning problem
 

OK. I have a 1990 Volvo 740 wagon and a question. My air conditioner is busted and the first mechanic theorized the freon was leaking from the compressor. So we got another one. But then we read somewhere that we'd need an accumulator. The mechanic confirmed this, so we got a used one and called yet another mechanic (problem diagnosed just before road-trip vacation) to put it in. Second guy told us we'd need a new accumulator because a used one allows moisture in, which is apparently not good. So two questions, really: Does anyone know if we need an accumulator for this repair? And do we need to get a new accumulator? Any help = greatly appreciated.

Short answer...Yes. The accumulator (also known as a drier) contains a bag of dessicant that removes trace moisture from the system. Odds are high any 20 year old used one you find is worthless. Once the system leaks down to atmospheric pressure moisture and any other contaminants find their way into the system.
By the way, rather than playing a guessing game, any genuine tech would add dye to the system before adding refrigerant so any future leak(s) can be traced.

I absolutely agree. The dessicant in the accumulator is kind of like a sponge, except that once it's soaked, it doesn't dry out. As a general rule, you replace the accumulator ( or the receiver-dryer on an expansion valve system ) any time you open the system, which of course you would have to do to replace the compressor. An accumulator from a wreck yard wills undoubtedly be saturated from being open to the atmosphere and will be about as useful as a blown fuse. If you buy a new one, you'll notice that the openings are all plugged and should remain so until it is actually installed.