After dancing the victory dance about my 87 190D Batt Drain issue, I have had strange partial failure of the Tempmatic System. A few nights ago I was traveling in a HUGE snowstorm, the Blower and Temp on Hi. As the car fought the blizzard, I got blasted by the depressing "blast of Burnt Electrical $omething" ! Not far from home, I parked it and planned a Troubleshooting session. Symptoms? The system went to default, full heat / DEF. After doing some button pushing today, I discovered that the System worked as advertised,(ie Temp Regulation, DEF/Floor/Side vents OK) EXCEPT on one button, the Floor Heat. It trips the default, until I shut off the car, that's all I get. Restart the car, and everything is OK, until I hit Floor, then the system defaulted to Hi Heat, DEF. Turn off car for a reset, same thing! 1) Can the CCU "break" in just one Button position? What can cause it? 2) Can the Switch block only fail? 3) The stench was TERRIBLE! Can just a partial failure, with no blown fuses, (lower Amp circuit)cause such a stench? Any thoughts? Thanks! BTW the PBU was a Reman installed 4 years ago....

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1987 190D 2.5 NA 1986 300E 5speed. ⬅️Stolen!

Guess you need to pull the glove box & look for melted wiring?

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MERCEDES Benz Master Guild Technician (6 TIMES)
ASE Master Technician
Mercedes Benz Star Technician (2 times)
44 years foreign automotive repair
27 Years M.B. Shop foreman (dealer)
MB technical information Specialist (15 years)
190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
Retired Moderator

Your HVAC control box is full of switches. They do get dirty.

I also do electronics repairs.

While I had the heater ripped apart on my 190E, I cleaned up and did a fair amount of circuit board soldering on my control unit. I found a cold solder joint at the fuse itself on my unit, for starters.

Mine is working fine now.

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My first Mercedes Benz. 4/6/07.

1984 190E (201 024) 2.3L four.