I started a new thread after replacing the Ign. Swith and Key Tumbler and I now have the proper voltage to fuse 11. Whoo Hooo !

I didn't before.

I did a write up on replacing the Steering Lock and Tumber and added it to the end of the last thread.


So making headway but not out of the woods yet. I'm starting to wonder if this problem now is what took out the Ignition Switch contacts. Hope not.

The steering lock is much tighter overall and the tumbler is nice and smooth so I should not get stranded on this failing.


What I have:

I have power 14V running in the fuse box on the Red/YL wire that I think goes down to the blower control and through it to the blower.

If anybody can point me in the right direction I'd greatly appreciate it.

Steve

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1982 300SD

Let me clarify:

U have voltage on both side of fuse 11. On the load side of fuse 11 the Red/YL splits to two Red/Yl wires. There is voltage on both the load legs now; ie both Rd/yellow wires.

Been reading a few posts, will look in AM and pull fan motor to take a look.

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1982 300SD

TS some today. No Voltage to blower motor. I have voltage to pin 12 on Electronc Unit for Blower Speed Control. I don't hear anything when I push button on dash for Climate Control. Fuse 10 tested and cleaned and voltage on both side of fuse. Tightened screw for Black/Red wire at load terminal screw. I have never removed the trim to get to the PB Unit for the Climate Control. Can somebody help me and tell he how to get to the Climate Control unit with the push buttons?

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1982 300SD

Prior to installing the new ignition switch the voltage to Fuse 11 would come and go. I'd wiggle the big plug on the back if it and the ACC system would run for a bit. When I had voltage, intermitently, it would be 14V till I put a load on it, then it would drop to 0. After replacing the "Ign. Switch, steering lock, and Ign. Tumbler" this voltage is rock steady at 14 V to and from fuse 11. Last night I temporarily wired up and sealed headlite beam to fuse 11, and the sealed beam lit up good. So now I know the Ign. Switch was toast and now new Ign. Sw. is passing the proper current and circuit will now accept a load without dropping to 0 V like it used to do. So I eliminated the main problem.

So this indicates to me that the Bad Ign. Switch, bad contacts, caused something else in the sytem to bite the dust. My theory is that if the Ign. Swith was failing "over the years", burned contacts, this must of caused failure somewhere else in the system. Any idea what component may have failed, and "where it is" and how would I test it?

Now I have no blower speed control, or any functions that I can see working on the ACC, at all.

Is there somewhere I can be pointed?

My biggest concern if messing with someting for no reason at all just to say I'm doing something and causing more problems than I have now.

I saw a Black box to the left of the Fan Blower Motor and I think the is the Electronic Blower Speed control box. It has power coming into it, I think it was pin 12.

With the system always running for 5 years or so, never a problem, I'm thinking it odd that I changed Ignition Switch and now nothing in the AAC system works??????

Steve

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1982 300SD

Set up the hot wire fused jumper (30A) to HOT pin (closest as you look at blower-plug) and fans runs smoothly and just a tiny load spark. Got behing the wheel and revved up engine and nice warm air out of vents, as before.

(Just swung around the plug to keep the back connection connected; ie the ground and touched the pin closest to me exposed now)

Adjusted the Thumbwheel for TEMP setting and the temp dropped when put in the blue range.

Push Button Unit (CCU)

It is getting power since I could hear an internal relay energize (K1) when I pulled off and put in C2 connector.

I"m thinking Blower Control Module but not sure possitively yet.

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1982 300SD

Checked voltage at PIN 12 on Blower Control Module, black box next to Blower Motor. 14V. Removed BCM and removed the plastic cover. Nothing in sideside looks burned and solder joints looks OK. Gently pushed on a few relays, no power on unit, and all seems normal. Reinstall. Goign to read up on taking apart the CCU, PB control.

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1982 300SD

Looked over CCU unit and replaced one previously intalled jumper on board. Reinstalled everything DEAD as a door knob.

This problem, no CCU functioning, just started before I installed the new ignition switch but I thought the problem was the Ign Switch. and not the CCU system.

Sort of lost after fighting this a full day and an half.

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1982 300SD

Looked around on Circuit board and determined one Diode bad. ID on diode is N400.

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1982 300SD

I tested the diode with my volt meter on ohm scale. It is the diode that goes to PIN 5 of the C2 connector. The way I remember testing diodes is to use OHM scale and try polarity both ways and it should read infinity one way and ZERO the other way. Testing of this black diode with a silve band around the end of it reads Infinity in both positionings of leads of voltmeter. So my assumption, as best I know of testing diodes, is bad.

I need to see if this diode is impotant enough to take down the whole CCU. It may be for a vent and not cause of the main issure.

A fellow member here offered to send me a known working CCU unit to see if changing them out gets my system running.

Mercedes went overboard on these things. I'd rather have a manual system.



Back to factory DWGS.

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1982 300SD

According to dwgs for air delivery this D4 Diode, Plug-C2 Pin-P5 is ouput to the input of the Automatic Blower Speed Control. Will see if I can find one at radio shack, meanwhile I have a CCU unit being shipped to me by a member that has been keeping up with this post.

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1982 300SD

All I can read on Diode is N400 the way it is postioned on the board. There may be a number after the diode. Anybody know the current rating of these output diodes? 1A is enough?

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1982 300SD

I meant to say there may be more numbers after the N400_ _ . I have not cut it out yet.

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1982 300SD

you're getting very deep into your CCU; i don't think any other members have. the furthest people go is resoldering some cold spots. i'm stuck with the autotemp II system (a la Chrysler) system on my 79 SD; it's very difficult to work on

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1983 300SD (daily driver)
1991 420SEL (work in progress)
1979 300SD (future replacement for 83 SD)

RIP:
1983 300SD (totalled)
1986 420SEL