There is a cartridge available from the forum sponsor. Cost of the cartridge kit is something like $35. Worth a try before getting too carried away with the A/C system. If the heat is stuck on, the A/C performance is going to be crap!

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Current stable:
1995 E320 157K (Nancy)
1983 500SL 125K (SLoL)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

Gone and wanting to forget:
1985 524TD 167K (TotalDumpster™) [Definitely NOT a Benz]