Brian,
I wish for SOMETHING to be the source of all my problems; anything.
Seriously, I have no deisre to get into the CCC if I don't have to. I saw the vacuum pods when i had the carpets out; I was impressed with how very organized everything appearded. I will tackle that area.
Thanks for the input.

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1982 300SD " Wotan" ..On the road as of Jan 8, 2007 with Historic Tags

The three most likely culprits (the duals) are accessed via glove box removal. The two dual for the main air door are right in font of you once the box is removed. The third dual, for the defrost flaps, is sitting at the very left side of the space, on a downward angle toward the windshield.

These pods develop cracks in the rubber diaphragms and the only good solution is to replace them if they don't hold vac. I recently did all three of the duals on the '87.

Does anyone know the answer to this question? I have a very specific and strange problem occuring with my climate control. I'll try to explain it as best I can...

My climate control system works perfectly, almost. I have the shop manuals and have verified that I get hot air where required, when required based on the various settings that can be selected with the controls. The only aspect of the system not working properly is the footwell ducts do not open when the economy putton is depressed on a heat seating. The strange thing is that when I measure the voltage at the changeover valve (the two-prong plug) that controls the footwell ducts with a multimeter, I get the requisite ~12V. The voltage at the changeover valve is correct in all settings. That is, 0V when the footwell ducts should be closed and 12V when they should be open.

Does anyone have any idea how the voltage is correct, but the changeover solenoid does not engage in the economy/heat setting?

To add to the mystery, the footwell flaps do open (the solenoid does engage) when the multi-level button is depressed (next to the defrost). Just to add a little info, I recently discovered that my aux. water pump was not working. I removed and tested the current draw... none. A continuity check from the postive prong to the negative reveals an incomplete circuit. Is it possible for an aux pump in such a state to fry the CCU as previously stated?

Thanks for any ideas.

If the AUX pump fused open, it is possible.

When can the aux pump fry the CCU? Does it fry the CCU in the process of failing? What I mean is, can a failed aux pump like mine continue to fry CCU after CCU if it is not removed from the system?

If an aux water pump draws more than 1.2 Amps, replace it. On the 124 CCU's if it is drawing more current than this it will indeed fry the CCU. I expect a similar result on late 123 CCU's.

Have a great day,

Mine has been unplugged from day one. I have it on the bench now and its totally corroded. Not fixable. I have always had plenty of heat, and amazingly enough, I seem to be in control of it--so

I also think you can bypass this unit entirely. My guess is its mostly for when idling. True?

That is what it is for, low-RPM. If you're fine without it, don't worry about it.

They are very available in junkyards though. The gasser 190s is a good source, Volkswagen VR6 had them, Audi 5-cyl. turbos had them, not sure of the pipe size and M-B has their own electrical plug, but look around and you'll find a cheap replacement if you're creative.

... or go without, sounds like it's no big sacrifice unless you idle for extended periods picking the kids up at school or something.

__________________

Gone to the dark side

- Jeff

what if it draws 0 amps? can it still fry the CCU?

If the pump's motor truly draws zero amps (is an open circuit or "burned out") then it cannot damage the CCU. To confirm this, you should unplug the cable at the pump and put an ohmmeter across the motor terminals. A burned-out motor will read infinite ohms. To be safe, leave the cable unplugged so that the motor can't "change it's mind" and suddenly start drawing current.

If you are getting sufficient heat and don't want to bear the expense of a replacement, leave it alone. To get a little more heat, remove the dead pump and bridge the gap with a piece of pipe. If that still doesn't provide enough heat, especially around town at low engine speeds (sitting in traffic, etc.) then you must replace the pump with a good one.

__________________

"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970

Have you checked continuity? Zero amps can be open circuit or direct short.

__________________
RRGrassi


70's Southern Pacific #5608 Fairmont A-4 MOW car

13 VW JSW 2.0 TDI 193K, Tuned with DPF and EGR Delete.

91 W124 300D Turbo replaced, Pressure W/G actuator installed. 210K

90 Dodge D250 5.9 Cummins/5 speed. 400K

So the 124's aux water pump is also not fused? Looks like I have another chore! By the way, I ended up putting a 2 Amp fuse in my 123. A 1 Amp fuse failed after awhile. Even though my measurements showed a steady-state current draw of about 0.9 Amp, there probably is a start-up surge of greater than 1 Amp.

__________________

"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970

I did the 1 amp fuse back in Sept. All is fine, currently, no blown fuse. IIRC the CCU could blow before the 2 amp fuse does. HAve you checked to see how easily your aux pump spins? Easier spin means less initial amp draw at start up.

__________________
RRGrassi


70's Southern Pacific #5608 Fairmont A-4 MOW car

13 VW JSW 2.0 TDI 193K, Tuned with DPF and EGR Delete.

91 W124 300D Turbo replaced, Pressure W/G actuator installed. 210K

90 Dodge D250 5.9 Cummins/5 speed. 400K

OPEN CIRCUIT AUX PUMP:
* corroded/age broken wire = may not have damaged the CCU.
* Fused open within the AUX pump = massive amperage spike through CCU = 99.99% odds CCU is damaged.

what else can damage the CCU? with the aux pump completely removed from the car, do I need to worry about the CCU being damaged because the aux pump isn't there to draw current as it normally would?