That's the one. It's the unit that issues commands to the compressor clutch, the black relay box to control the fan speed, and monovalve/aux pump. It's basically the "brain" of the system, so when it gets issues the HVAC system gets a mind of its own.

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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]