The expansion valve is above the accelerator pedal next to the firewall. It is a BEAR to get to. There is a sort of crash "cage" thing in your way to get at some of the fittings, removing the bolts that secure it allow you to move it out of your way. Have some crows-feet ready (17mm, 19mm, 22mm), plenty of swear words at the ready, and be prepared to do some contortions.

The job isn't difficult, it's just the access that's a SERIOUS PAIN! Start to finish, the job should take you about 90 minutes.

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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]