Inside the box: W126 Automatic Climate Control. First Gen. - PeachParts Mercedes-Benz Forum

JamesDean · #1 07-05-2012, 04:10 PM

Hello everyone,

Forum member mccauleybil sent me his climate control unit to see if I could repair it.

He sent:

126 830 02 85 Climate Control Push Button Unit
126.032 - 380SE
126.033 - 380SEL
126.037 - 500SEL
126.043 - 380SEC
126.044 - 500SEC
126.120 - 300SD

000 822 09 03 Temperaturregler.
126.032 - 380SE
126.033 - 380SEL
126.037 - 500SEL
126.043 - 380SEC
126.044 - 500SEC
126.120 - 300SD

I took apart the PBU and discovered that there really isnt much to go wrong inside this unit! There are a few relays, diodes and resistors and thats it!

What I did see that could go bad are a large amount of solder points on the back.

The temp setting wheel also contains some interesting circuitry. There is a small 10k pot mounted at the center of the wheel. There are also three traces that the unit uses as a potentiometer as well. Now from all the other trace style pots that I've seen there has always been a carbon coating present, however this was not the case. I'm not sure if its simply eroded away over the years or simply was never present in the first place... I dont have another PBU to disect for comparison.

PBU Pictures:

JamesDean · #2 07-05-2012, 04:10 PM

PBU Pictures #2

JamesDean · #3 07-05-2012, 04:19 PM

As I mentioned before he also sent in this "Temperaturregler" unit.

000 822 09 03
126.032 - 380SE
126.033 - 380SEL
126.037 - 500SEL
126.043 - 380SEC
126.044 - 500SEC
126.120 - 300SD

Its worth pointing out that this unit is not available from most parts houses. I checked with XXXX ordering through the dealership and the "online price" was $522!

I opened the unit up and found that the large axial capacitor was broken loose. Its fairly easy to wiggle around. I checked and its still holding proper capacitance. I'm planning on stripping the coating off this board and re-soldering it. Also you can see several broken copper pieces that go from the board to the pins... I suspect this was causing quite some problems.

The Temperaturregler actually does quite a bit of the leg work for the climate control unit. I suspect that much of this circuitry was integrated into the later 2nd gen units.

From the ETM the following are hooked into the Temperaturregler:
1- Heating Enable
2- Center Flap Control
3- Automatic Slower Speed Control
4- Fresh/Recirculated Air Control
5- Monovalve Heater Water Valve Control
6- Set Temperature Input
7- In-Car Temperature Input

Pictures:

I went through and re-soldered everything, the large capacitor's solder joints were broken on both leads. I repaired the main contact connections, they should do much better now. I think, while its open, the electrolytics should be replaced as well however I don't have any of these sizes in stock so we'll have to see what its owner wants to do..

Gilly · #4 07-05-2012, 04:34 PM

Is this the original style temp control or the version with the mono water valve (second version)?

JamesDean · #5 07-05-2012, 04:39 PM

Quote:

Originally Posted by Gilly

Is this the original style temp control or the version with the mono water valve (second version)?

This would be the type with the monovalve.

Gilly · #6 07-05-2012, 04:43 PM

OK, I didn't think the first gen, original 126 chassis has the monvalve, I thought they has that electric/vacuum servo water valve, what do they call thatthe "Darth Vader" valve? R2D2? Something like that.

Gilly · #7 07-05-2012, 04:49 PM

OK I found info on the system I was thinking of. The era was the same, but evidently not on 126's. I remember working on them in 116's and 107's I guess. Link to a pdf, really good article on them:
http://www.google.com/url?sa=t&rct=j&q=&esrc=s&frm=1&source=web&cd=10&ved=0CHYQFjAJ&url=http%3A%2F%2Fuserweb.windwireless.net%2F~jimc%2Fchryaccfh%2Facc2servo.pdf&ei=1P31T8iqAcXJqgGh3_iJCQ&usg=AFQjCNHSyqC2PsFu16j_WaBtmUUsHOyvVQ

Gilly · #8 07-05-2012, 04:52 PM

Reason I asked is because if it were the system I was thinking of I didn't see the amp disassembled

JamesDean · #9 07-05-2012, 06:33 PM

Quote:

Originally Posted by Gilly

Reason I asked is because if it were the system I was thinking of I didn't see the amp disassembled

Ahh. I've never worked on/encountered the earlier electro/vacuum servo type. All my cars are 82 or newer.

Gilly · #10 07-05-2012, 06:43 PM

Right, and according to the PDF they used this up to 1981, so I was off by a year. I know the 126 was introduced in 1980, so I thought by default the first gen of 126 ACC were this older style. Bear to work on.

compu_85 · #11 07-05-2012, 06:55 PM

W126 production started with the climate system pictured, they were the first to get it. 1985 W124 cars got their climate system first, and it was installed into the W126 for 1986.

The GenII (W124) system does not have the separate "smarts box", everything is done by the bushbutton unit.

-Jason

JamesDean · #12 07-10-2012, 07:32 PM

Replaced Capacitors in the Temperatureregler!

balwit · #13 01-22-2013, 09:11 AM

Can anyone here point me to a good diagnostic guide for sorting out the climate control system in my 300sd. Suddenly stopped working.
Also, if there was a good article describing the big picture functioning of the system that would help too. If I could find a way to jam the water valve to the on position I could at least use my car while I muster the courage to tear into the system.

Thanks.
John Balwit

big dog 2 · #14 01-22-2013, 09:42 AM

Nice work!

I didn't have the smarts or patience to fix my old one. Got a couple from Pic & Pull instead.

strelnik · #15 10-31-2018, 12:32 PM

Quote:

Originally Posted by balwit

Can anyone here point me to a good diagnostic guide for sorting out the climate control system in my 300sd. Suddenly stopped working.
Also, if there was a good article describing the big picture functioning of the system that would help too. If I could find a way to jam the water valve to the on position I could at least use my car while I muster the courage to tear into the system.

Thanks.
John Balwit

John,
I am looking for the same thing that you are. I'll copy one if I find it first