Quoted From johnbkobb:
It’s bad if it has been in the system sucking up moisture and becoming saturated. Whenever the system is opened it MUST be replaced you can’t pull the moisture out of it with vacuum. You can’t recharge them with vacuum they MUST be replaced.
If you’re going to open the system I would advise a system cleaning and replacement of all the O rings and S valves (2 — hi and low side). If there was excessive moisture in the system acid has probably formed inside due to the moisture. After you have your system evacuated of refrigerant give it a good cleaning, install the new receiver drier, vacuum and check for leaks, add the proper refrigerant OIL for what your system needs (less the OIL left in the compressor) do not overfill. Then charge the system with the R134a
FYI if you just replace the receiver /drier you need to add the correct viscosity refrigerant OIL back into the system to replace what will be removed when you take out the old receiver drier. Check the pump manufacturer’s specs for the recommended viscosity of refrigerant OIL to use with that pump and check the vehicle manufacture’s specs as to how much refrigerant OIL is used in the system and how much is attributable to the receiver / drier and only add the amount attributable to the receiver / drier back into the system. It is important not to over or under fill on the refrigerant OIL. Also check the specs on how much refrigerant (R134a) the system needs and do not over or under fill. These are important to obtaining the best efficiency from your A/C system.
Awesome! I was too lazy to type all this but you hit the nail on the head