Greetings! New to the forum, and glad to be here. I have already saved myself close to 3k in labor costs by reading the replies from previous questions, so thanks! I own a 1990 300D 2.5 turbo diesel with 110,000 actual. My current issues:
1. I have searched everywhere for a vacuum diagram detailing the climate control system. My driver side dash vent is dead (middle and passenger vents expel copious amounts of air), and the system will randomly switch from dash to feet to defroster locations on its own. A/C air is nice and cold and heater works great, just above issues.
2. My speedo needle started bouncing between 40-80mpg two weeks ago and last week both speedo and odometer quit working at the same time. Took speedo cable off mounting at trans and probably 2oz of water poured out of cable housing. Removed cable (I noticed that the connection at the back of the instrument cluster was a little loose), no obvious breaks or kinks, cleaned cable , blew air through cable housing to remove any remaining water, checked that both ends of cable were intact and turning and reassembled. Now speedo works like new with no bouncing, but odometer is still completely dead.
Any suggestions greatly appreciated...

I disassembled my odometer the other day and it had a broken gear. Not something I could fix. I guess its pretty common on the older cars, not sure if you have a mechanical or a digital odometer in your car but if it is mechanical that is probably the issue.

__________________
1981 300TD
2005 C55
2004 E500
1999 ML430
1992 400E
1998 C43
2001 SL500
1988 300SEL
1986 190E 16V
1991 190E 2.6

My odometer is mechanical. I noticed on DieselGiant website that he has a DIY section on repairing a broken gear problem, but after calling the MB dealer nearby was told that the gear assembly for these older cars are no longer available from MB. Any leads on odometer workings OR the 1990 W124 climate control vacuum diagram?

On the odometer:
Remove the gauges from the gauge face and look into the speedo. At the end of the axle that holds all of the odometer number wheels is a white plastic gear. The gear likely has slid toward the end of the axle allowing it to disengage from the worm gear that should drive it. Push it back on (but not too far as to cause it to bind). Careful, you want to push it on squarely and avoid splitting the gear (if it isn't already, usually not). Heat will help, the plastic of the gear will grow at a rate much higher than that of the axle as it heats up.

If you can put a little glue on the end of the axle to prevent gear slippage from re-occuring, that will prevent doing this again next spring. If you could knurl it or otherwise rough-up the axle, ... not much space to do that though so glue is better than nothing (I prefer a two-part epoxy, JB Weld will probably work also).

The Climate Control is designed to change where it blows depending on what it's doing. On the two all-direction button settings it will use the floor and defrost primarily for heating, as the temperature setting is satisfied it will use the dash vents more, and for cooling the cabin it will use the dash vents. Set it all of the way hot and see if it stays blowing on the floor.

Is the left vent shutoff flap broken? If the flap isn't opening/closing with the wheel on the vent face that's an easy fix. I believe that the left and right vent come from a common plenum so that's the simplest explanation, and vents are easy to replace.

If the Climate Control Unit (pushbutton unit) is bad, it will blow all defrost/vents usually (no floor). The normal explanation to a bad CCU is a bad auxiliary pump (the electric boost-pump in the hose to the heater core) drawing too much current and damaging the CCU.

__________________

Gone to the dark side

- Jeff

greeting all,

i'm having similar issues with the heat in my 83sd

for a while i only got defrost. then only defrost from time to time. now not at all except once in a blue moon when i first turn on the ignition.

i changed out the blower motor regulator with no joy.

i guess next is the CCU.

interesting you talk about belt slippge as a cause of incorrect voltage to CCU as I am hearing belt squeal at low speeds.

i had the voltage regulator fixed a while back. maybe that was a cause to woes. at that time the radio stopped working. but strangely enough there is power to the radio because the light comes on.

any help is appreciated.


83 300sd
275,000
biodiesel
saved from crusher in junk yard

"1. I have searched everywhere for a vacuum diagram detailing the climate control system. My driver side dash vent is dead (middle and passenger vents expel copious amounts of air), and the system will randomly switch from dash to feet to defroster locations on its own. A/C air is nice and cold and heater works great, just above issues."

If the middle and passenger vents work then either the driver side vent is broken in the closed position or has come unhooked in the back. If you pull the cluster out I believe you can see if it is connected or not.

Does the system switch on its own, or are you turning the temp. wheel or pushing different buttons to make it blow out of the different outlets?

__________________
1987 300TD 309, xxx 2.8.2014 10,000 mile OCI


Be careful of the toes you step on today, as they may be connected to the ass you have to kiss tomorrow. anonymous

“Be who you are and say what you feel, because those who mind don’t matter, and those who matter won’t mind.” Dr. Seuss

I will have to check to see if the left dash vent is disconnected when I pull the dash to check on the odometer issue. The left vent manual shut off does work when the wheel mechanism is turned to the off position on that vent, so I suppose the vent has to be disconnected or blocked in some way, especially if the left and right dash vents work off the same vacuum pot. The system will start out working right as indicated by the button on the CCU that is pushed, but will then randomly (and usually as or after I have accelerated the car quickly) change the location from whence it is blowing. Of course, the left dash vent NEVER blows any air at all, regardless of setting. I will investigate the pattern of button operation further and report back, but is this sounding more and more like a vacuum issue?

No, if it were a vacuum pod issue, it would not switch between all the outlets. They wear out and then it defaults to the defrost outlets. It sounds like a CCU issue to me. I only have experience with the vacuum pods. There are plenty of posts here about the CCU. Use the Google search feature at the top of the home page to search for them. It will give you better results than the one on this page.

__________________
1987 300TD 309, xxx 2.8.2014 10,000 mile OCI


Be careful of the toes you step on today, as they may be connected to the ass you have to kiss tomorrow. anonymous

“Be who you are and say what you feel, because those who mind don’t matter, and those who matter won’t mind.” Dr. Seuss

Thanks to Babymog I now have a working odometer! Spent Christmas evening with the instrument cluster disassembled on the kitchen table, and the issue and solution was dead on! The only difference in the gear problem was that for Babymog, the plastic gear itself had slipped on the drive axle, and for me the problem was that the entire axle had finally shifted enough so that the round gear on the axle was no longer in contact with the worm drive. After confirming that the worm drive did in fact spin and the numbers move (using the kitchen match in the speedo cable port mentioned on the forum elsewhere), I simply, and carefully, slid the entire axle back into its' original position and voila! a working odometer. Unfortunately, I could not see a way to apply any permanent fix, as the round plastic gear itself would not slide on the axle, and I was not willing to apply excessive force to the gear. But if it takes another ? months or years to work itself back out I am satisfied for now. Thanks for the great tips on the speedo and odometer repairs, and I will update on my CCU repairs as they occur. Vespucci

^^^ Lucky.......

__________________
1981 300TD
2005 C55
2004 E500
1999 ML430
1992 400E
1998 C43
2001 SL500
1988 300SEL
1986 190E 16V
1991 190E 2.6