You can get to everything to test it without pulling the dash. If you have a dead vacuum pod, some can be accessed without pulling the dash, others require dash removal or a screw to prop the flap open. The monovalve is energized to close, so if the silver box is screwed up and running wild, you can expect the heat to be on pretty much full time.

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Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

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