I think I'll go to the Pick&Pull and get a spare PBU. There are 3 donors from 83-85, my 300SD chassis is a 1984.

I'm in Idaho and the heater is presently working. When I fiddle with the PBU a bit the clicking stops and the heat comes out of the windshield vents and the side-dash vents.

The last thing I want is to do is "fix" it until it is well and truly broken before Spring.

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1st MBz: 1982 300SD
2nd MBz: 1987 300SDL
3rd MBz: 1995 S420
4th MBz: 1987 190DT
5th MBz: 1984 300SD w/1983 300DT engine
6th MBz: 1999 C230k I'm 3rd owner, got it w/57,235 miles.
and manages Mom's 2007 R320 CDI