They probably just opened it up, cleaned it, and put a new dessicant bag in it --> for $185. The drier is used to pull any moisture out of the system.
Make sure that your o-rings on the fittings are in good shape. When they changed over to r134A, they used PAG oil in the refrigerant to lubricate the compressor. They also changed the o-riongs to HNBR which is a green rubber to be compatible with the PAG oil. I saw at either Lowe's or Home Depot in the fastener aisle that they carried a box of different size HNBR o-rings.