In prior times, changing the receiver/drier was never a real issue. As long as the system was sealed and charged, things worked OK and if you ever fully evacuated the system, it was supposed to pull all of the moisture out of the system when you did that. I do seem to recall that somewhere in the middle 1970s, the production Chrysler receiver/driers were downsized to basically 1/2 of what they previously had been--not sure if it was an engineering decision or an accounting decision.
Somewhere, things seem to have changed. I've noted a new orientation to change the drier if the system is over about 5 years old, kind of like routine maintenance, due to the dessicant in the drier wearing out or something. I'm not sure if the dessicant in the newer driers is less volume than before or if it has been determined that more moisture can seep into the system than we previously thought happened.
Many aftermarket air conditioining suppliers plainly state that if a compressor is replaced, unless the drier is also replaced at that same time, they will not honor the warranty on the compressor, especially if any "trash" is in the system. Trash from a compressor failure can apparently puncture the dessicant bag and then that TOO gets into the system.
The old solvent-style a/c system flush first got extremely expensive to purchase and then the EPA basically outlawed it (VOC content?). Now, the only choice is to add an in-line filter and change the filter when it starts clogging up.
End result, what the guy at the parts store was "reciting" was the latest information from their suppliers. Not specifically just to sell you something you perceive you might not need, but to hopefully save time and money in only doing the repairs once.
There are some companies that can rebuild receiver/driers. Many of the newer versions might not look exactly like the OEM production unit on existing vehicles so for those who can't find one that looks like their old one, rebuilding might be an option. It would take special tools and a heliarc welder for the newer aluminum bodied driers. Therefore, no user serviceable parts in that unit.
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