replace drier when servicing R134a system?
 

This is primarily a non-MB question but there might be generic value. So if Brian and Jim will indulge me -

Our 97 Caravan is the shop for a hissing AC system. Low charge attributed to a leaky high side hose. Should I insist that the drier be replaced or will a proper vacuum boil off whatever moisture is absorbed while the system is open? The cost of a drier is trivial but the shop will not throw parts at me.

Thanks,
Sixto
87 300D

No. Mosture that has been absorbed by the dessicant in the drier will not be removed by evacuation. It is good practice to replace the r/d any time the system is opened and especially if there is a history of regrigerant leaks.

Amen.

If you end up replacing the A/C Compressor some places will not honor the extended warrentee if you don't replace the drier and the expansion valve.

Dryers are pretty cheap. I usually change them out anytime I have systems open.

The drier will hold a small amount of refrigerant oil too. They should add an ounce or so.