I hope I'm doing this post right. In my surfing I found instructions on rebuilding seat cushions using pool noodles - I think on this forum under another topic.

Also, my thanks for a run down on ccu issues. Mine seems to fit the solder cracks discription in that some times it doesn't work at all and other times it works great.

Charles

I'm one of the "lucky" few who've had the blower resistor fail. One of the coils just burned-up. I ohm'd-out about everything imaginable, installed two different CCU's that I'd repaired and that worked perfectly testing them (at least till this point) and checked everything you could imagine. I would never have imagined the blower resistor going out. It did though, so ever since then, I pull them at the junkyards and have a dozen or so in parts stock in the basement....

OK, so I'm obsessive about not having to pay retain for something if it breaks....

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1984 300D Turbo - 4-speed manual conversion, mid-level resto

1983 300D - parts car

1979 300TD Auto - Parts car.

1985 300D Auto - Wrecked/Parts.


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"If you don't know where you are going, any road will get you there". Lewis Carrol

dude! that's the car making sure it doesn't overheat! It's alive!

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1964 datsun 1500
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this is where I quote some dude, so I look smart because of quoting that dude that said something smart once

i found out this weekend that ACC units are not universal between 123 and 126. bummer.

my unit works okay, i.e. does not need resoldering, but sombody fat fingered the buttons and broke the spring keepers off most of them. as far as i can tell, i need to completely unsolder them from the boards and replace the whole pushbutton thingy. Anyone got a trick to replace the button posts without removing the whole switch body?

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84 300SD ODO broken at 277k
02 Jetta TDI
KHS roady, stumpy hardtail- powered by carbohydrates
OBK56

I soldered up the CCU and cleaned out the fan switch, but I still have no fan control. The rest of the CCU seems to work fine. I also cleaned the contacts on the sensor just above the thermostat housing with no joy. What is next, the fan its self?

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1979 240D- 316K miles - VGT Turbo, Intercooler, Stick Shift, Many Other Mods - Daily Driver

1982 300SD - 232K miles - Wife's Daily Driver

1986 560SL - Wife's red speed machine

The fan (easy to test with jumpers, at least at full, 12v setting) or the resistor, located on the firewall, usually pass side in engine compartment.

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1984 300D Turbo - 4-speed manual conversion, mid-level resto

1983 300D - parts car

1979 300TD Auto - Parts car.

1985 300D Auto - Wrecked/Parts.


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"If you don't know where you are going, any road will get you there". Lewis Carrol

OK, I've been reading and posting on the forum for a couple of months and I've got a good understanding of the dozen or so problems and how to fix them including resoldering the CCU. Just need more wrench time.

For years, our 83 300D has had a tempermental CCU that works sometimes. Today it was the defog windshield that would not come on (no fan at all). For years now, my wife fixes these problems by shutting the car off and restarting - problem goes away about 75% of the time. It makes no sense to me why that would work.

After about 10 minutes of her nagging today, I pulled over turned off the engine, waited her prescribed 10 seconds and restarted. Defog can on immediately and worked the rest of the way home. She even cycled it to regular vent and back based on fog and temperature needs.

The only way I can contend with her smug "I told you so look" is to come up with an explanation as to why her method works.

Please help - the masculine dominance in car repair needs redeeming!

Charles

This sounds more like a blower motor problem, rather than a CCU problem. If the blower motor brushes are extremely worn, you will get just the problem you are describing. Replacement brushes are available at www.**************.com but if the commutator is worn, you will need to change the blower motor.

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Sam

84 300SD 350K+ miles ( Blue Belle )

That was my thought a month ago. I found a good assembly at the bone yard, replaced the brushes, commutator looked fine. No change in random behavior.

But why would turning it off and back on change anything?

The CCU pushbutton unit mainly controls the mode of operation and temp. selection.
The Blower Speed Controller and of course, the blower itself, for airflow.
Then there is the Temp. Controller for using inputs from the CCU and Temp. Sensor to control the blower speed, monovalve and a/c compressor via the pushbutton control.

Is only the blower cutting off? or is it not changing modes? or do you lose control of temp.?
Turning it off to reset could be a heat factor with an electronics assembly.

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Sam

84 300SD 350K+ miles ( Blue Belle )

With the blower not running, it's hard to tell about mode but I don't think it is switching. The pushbuttons seem to do nothing. There seems to be no control of temperature. There is a little warm air coming out the vents but not with fan assistance. I think it is bringing in outside air over the heater core.

Have you checked fuses?

Have you opened and resoldered the CCU Controller?

I guess I don't understand what you have done so far to resolve the problem other than change out the blower motor with another used one. BTW, I went through two used blower motors in short order (less than 6 mo.) and decided to put in a new motor and be done with it.

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Sam

84 300SD 350K+ miles ( Blue Belle )

Sam,
Most of the fuses are the originals (25 year old and aluminum). I've ordered the new style brass ones and will replace all as I clean terminals.
The CCU was resoldered about 3 years ago.
I've got low vacuum and a noisy pump - replacing it this weekend and then checking for vacuum leaks.

I've got a plan and I'm sure I'll get it fixed.
Question is:
"Why does killing and restarting the engine make it work"?
Often if the system is working and you stop and restart soon, it will quit working. This is the baffling part that my wife is so smug about because her method works and I can't explain why.

Charles

PS: What's the trick for removing the plastic fan without breaking to replace the motor? The entire assembly new is too expensive. The motor is reasonable but it looked like I would probably break the fan trying to remove it.

Well, I don't know if I can completely explain why shutting it off and restarting causes it to work. (And having been married before, I know that you will probably never prove your wife wrong as long as she thinks she's right, in her own mind.)

With the vacuum pump marginal and fuses on the edge, resolving both of those issues may do the trick to cure the intermittent problem. Check those fuses closely as I had one that gave me fits because of a hairline crack where the end cap met the fusible strip.

To remove the fan cage, support the cage really well on two sides and a good whack with a drift punch causes it to drop right out. Be sure to have something to cushion the motor when it drops as it usually comes out with one blow. (They must build both of those parts with very exact tolerences to cause a "press fit" to be so snug.)

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Sam

84 300SD 350K+ miles ( Blue Belle )

Now that I've found the problem, it all makes sense. I was not always getting current through the ignition switch to various switch on features including the CC system. Problem seems to be solved with new ignition switch.

I don't thing I've seen that listed in CC issues.

Charles