Getting somewhat interested in the recent failure of one of my Climate Control Units, I've torn a few apart for a visual.

The one that failed, failed with the phantom on problem, ... it would turn on the A/C on Econ, and sometimes the A/C and blower would come on with the unit set to O/Off.

The failed unit was OE, in my '87 300D. It is a non-Bosch.

I sat down with 5 units:
New Bosch
'88 Bosch (300TE)
'87 Bosch (300E)
'87 HK (300D)
'87 HK (300D)

The Bosch is identifiable by the black tape squares visible with the zebrano panel removed, the Bosch sticker, and the finger indents inboard of the connectors on the (taller) circuit box. The HK has a Mercedes emblem and HK stamped into the case plastic. My new Mercedes unit is a Bosch, could be NOS however.

The one that died, is the '87 300D HK unit. That car now has the new Bosch, may it heat and cool for a very long time.

The dead HK unit has a heat-discolored area in the center of the main circuit board, telling me that it was not designed for the current it has been handling. This car has recently also had a blower and blower control replacement, the old parts might have been the cause. This was a Florida car all of its life, little heat and much A/C.

The other HK (working, in my other '87 300D), has the same discolored area, but is still working fine. I will be pulling the blower soon to see if it is in good condition, ... would be interesting to compare amp-draw to the new one in the blue car. This second car was a Michigan car all of its life, less A/C and more heat.

The Bosch units would seem more robust, as neither of them have any discoloration of any part of the circuit board or the components. All of the units, both manufacturers, had the standard green FR4 circuit board substrate.

Might be luck, perhaps the cars from which I pulled these units had excellent maintenance all of their lives, both gas cars, both in the quarter-million-mile range, but if so then they would probably not be in the boneyard.

I'd be interested in finding which of these, Bosch or HK, are failing. Since there are some possible failures posted recently, please post which unit failed.

If I were picking used units from the boneyard, I'd be looking for two things:
1) Look for a farenheit wheel. The Celcius wheel is pre-'90.
2) Look for the Bosch unit. Should see the black tape when the zebrano panel is removed. If HK is found on it, my "research" so far indicates that it is less likely to survive.

Any additional data is appreciated, post your failed unit's failure mode and manufacturer please.

__________________

Gone to the dark side

- Jeff

BTW, if someone wants a 201 CCU project, I have a couple of CCUs that could become one good one:

The CCU in my 190Dt failed, seized aux. pump, and burned out a transistor (obvious when opened). Would no longer run the aux. pump or the blower.

The other one is a used CCU that I acquired, which has a bad pushbutton assembly, but good electronics.

It is for the '87-up 201 Climate Control, pay me for shipping and it's your project. Ya might learn something, like why I decided to buy a new one instead of mess with this LOL.

__________________

Gone to the dark side

- Jeff