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

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

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

time to get the soldering iron out....my AC weirds out on me and switches to the DEFROST vents; turn off ACC for 5 seconds; turn back on....and vents switch from DEFROST to DASH. Weird. Glad you guys have already gone thru this ahead of me....would drive me crazy.

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daw_two
Germantown, TN

Links:
Sold last car --- 05/2012 1984 300D Light Ivory, Red interior
No longer selling Cluster Needles Paint
No longer selling New Old Stock (NOS) parts

Past:
3/2008 1986 300SDL "Coda"
04/2010 1965 190D(c) "Ben"
& many more

Mine was doing this and I replaced the ignition switch to clear up strange problems like dash inicators coming on at odd times. Looks like it cleared up my weird acting CCU also.

My theory (open to comment and revision) is the ignition on position supplies current to the CCU. If this was interupted by sporadic shorts in the ignition switch, the CCU would be getting current on and current off signals causing it to be confused.

Plausible?
Charles

I posted in the parts section two used ones that I was trying to solder if anyone wants to buy them to play with or for cores.

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Current Stable:
1994 S500 v140, 210k miles, white with grey.

Former Mercedes in the Stable:
1983 300CD Turbo diesel 515k mi sold (rumor has it, that it has 750k miles on it now)
1984 300CD Turbo Diesel 150 k mi sold
1982 300D Turbo Diesel 225 sold
1987 300D Turbo Diesel 255k mi sold
1988 300 CE AMG Hammer 15k mi sold
1986 "300E" Amg Hammer 88k mi sold (it was really a 200, not even an E (124.020)
1992 500E 156k mi sold
etc.

I have a few extras that I was going to resolder, but I bought a rebuild programma one. I have the extras on ebay, item # 220235685135

So you guys can play with them. $0.99 start bid, ends this weekend to be fair to everyone that cant log on during the business day.

I drive a 1989 300sel (126? )

OK i need some help this is driving me crazy, the climate control seems to have a mind of its own, it seems unwilling to change what its doing. IE Ive had air conditioning running now for 5 weeks, before that i could only get the heater running.

so far i have not tried that much all i have done its pulled the climate control module out and done a blanket resoilder of the hole board (part number 1268300885)

It used to be that you could get the climate control to change by switching the climate control off when the motor was running. then turning off the motor, changing all the setting then starting the motor again but that no longer seems to help

sometimes when i start the car it seems to think about putting the heater on (you know how it seems to like blowing air at your feet when its heating and blowing air at your face when its cooling.....) but then it stops for a second and then i think it starts the compressor, i can hear the load on the motor

as a test i disconnected the mono valve and now i think i have the air con running and the heater at the same time (the temp wheel is set to max heat)

oh most of the system is working i can adjust the fans and i can put demisters on and i can turn it off the only thing I'm having problems with is temperature. the temp wheel seems to do nothing




now the things i think it could be after reading all of your posts

1/ ignition switch -seems very odd and i think mine has been replaced all ready but did they stuff it up some how?

2/ The push button climate control module its self - even though i have resoldered all the joints i still wonder about that Potentiometer (the temperature wheel) maybe its intermittent ?

3/ the device that senses the temperature in the car - think this is the most likely culprit but don't know were its located any one know ?


is there anything i could have missed ? thanks for any help