ACC - Blower only working for defog - PeachParts Mercedes-Benz Forum

#1 11-15-2005, 02:21 PM

The car in question is a 1980 300TD. I got it from a yard, where it had been sitting for a while. Anyway, I have resolved a bunch of issues, and the biggest one I now face is the climate control (besides the mildewy smell... yuk).

The blower motor works on defog... its sending the full voltage at that point. With the other push buttons (this is the vertical push button setup), it is only sending 0.5V to the blower motor. I haven't done much work with climate control, so I am a little clueless here. From searching archives it looks like the defog kicks in a higher power blower than the others?

Based on some of the information that I had seen in the archives, I yanked the unit (poor choice of words) to look for places to resolder. The controls look way different than the horiz. push button units and it didn't seem that there was anything I could resolve there (btw... that thing is a PITA to remove!)

The only other issues I see are these... not sure if they are related. There are two vacuum hoses that dead end (open) in the vicinity of the blower (they enter the firewall near the battery). One is black (with the other 123s I've worked on these were typically for venting... is that the same in this case?) and the other is white. I can't find any places that these might connect and review of the engine vacuum diagrams does me no good. The other issue is a crack in the plastic elbow connecting a fitting in the sidewall to a fitting to the side of the blower unit.

Any ideas?

namron4491 · #2 11-15-2005, 03:03 PM

I'm having the same problem and want to pull the unit out, But what all to you have to remove to get it out? thanks Norman

#3 11-15-2005, 03:38 PM

There are four mounting screws... two on each side near where the console trim meets the carpet. I had to remove the console to get to the screws. I had a difficult time manuevering around the arm rest...

#4 11-15-2005, 10:22 PM

Anybody?

pmari · #5 11-16-2005, 01:11 AM

http://wagoneers.com/DieselBenz/TECH/climate-control.txt

Also try the search, there is a good thread on resoldering the climate control.

I have also read where spraying electronic contact cleaner in the wheel and push button assembly may cause stuff to work again.

#6 11-16-2005, 08:06 AM

Thanks, pmari...

I found the resolder thread before, but this climate control unit is substantially different than the ones discussed (at least, the ones I've SEEN discussed). Can you tell me more about this foam tube? Mine had disintegrated and I replaced it with a vinyl-ish tube. Will this not work? Where can I find a replacement tube?

SD Blue · #7 11-16-2005, 10:22 AM

1980, Isn't that one with the servo unit? If so, a search under "servo" might give you more answers. Some have successfully repaired theirs. A new digital option is available at www.performanceproducts4benz.com but is a little pricey at about $700.

kerry · #8 11-16-2005, 10:55 AM

Yep, should have the dreaded servo unit. I believe I'm correct in thinking that a bad servo can cause the symptoms you describe. You can get rebuilt servos, some with an aluminum base as opposed to the plastic case. It doesn't sound like our car justifies the Performance $700 upgrade but I think a new servo, if you can find one, will run around $900.

If you don't know what the servo is, it's the large canister type device mounted on the fender just to the right of the front of the engine. It has a bunch of vacuum lines and wires going in to the top and heater hoses at the bottom. It was designed by Satan himself and then perfected by British engineers at Lucas.

#9 11-16-2005, 11:19 AM

Is this the servo unit?

kerry · #10 11-16-2005, 11:21 AM

That's it.

#11 11-16-2005, 11:22 AM

I got the other buttons to work when I pulled on the arm of this device (sorry, I can't find the name of the part & the lighting is bad). It's located behind the glovebox and has some vacuum lines in it.

The car also doesn't shut off with the key. I've checked all of the engine vacuum diagrams and all seems in order there. I mention this b/c it seems related...

#12 11-16-2005, 11:23 AM

If I have another servo, is it an easy swap? And how would I test either one of them?

kerry · #13 11-16-2005, 11:29 AM

That's a vacuum pod. There's a diaphragm inside. It's probably failed and needs to be replaced. There's a company that will sell you diaphragm replacement kits. I can't remember the name, but I think it has the owner's name in the name of company. Goerge ...... perhaps. A search should turn it up.
Not a big deal to replace the servo. The vacuum and wire connections come apart quite easily and then you have to remove the heater hoses.

I don't know how the bad diaphragm factors into the equation. It is a complicated vacuum system and perhaps a bad pod can induce a series of other problems. You should at least pull the vacuum line from the problem pod and plug the line and see what happens then before replacing the servo.

Servos often fail because the bottom case is plastic. It cracks and then the valve can't turn. There is a diagnostic procedure. You'll need the entire written instructions to run the tests. It is not easy. I believe they are on file in the library at Hades.

#14 11-16-2005, 11:56 AM

The first few times I pulled on the arm, the heater stayed on. Now it turns on momentarily before a click behind the ACC unit turns it off.

I have some research to do on Western "civilization"... I guess the servo information now gives me two reasons to go to that library....

kerry · #15 11-16-2005, 12:15 PM

I've experienced similar symptoms with a pod. What happened the first time was that when you pulled on the pod, the compression you caused in the diaphragm closed the hole/leak and the diphragm pulled itself tight. Now the hole has gotten bigger and it can't actuate itself at all.
Plug the line to that pod and see what happens.