I'm just at a bit of a loss how smoke possibly from the CCU could get up into the center vents. The vents are ducted while the CCU is just hung in the middle of the dash. If something fried in the CCU I would think some smoke might come out somewhere, but not necessarily from the vents.

On my car, one of the main power cables to the blower motor decided to fry itself quite close to the blower motor itself, causing mass quantities of smoke to come out the vents. All the vents. Scary quantities.... Not to mention that smell...

I was relieved to find it was only the cable and I spliced in a new section which has worked for a couple of years. Of course one has to take the blower motor out to do this, which is tedious in a 124.

Sorry to not be of much help!

Rgds,
Chris W.
'95 E300D