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turbodiesel 12-19-2002 10:13 PM

300SDL climate control
For the last week or so, my climate control will not work until the car has been driving for atleast 15 minutes. No heat, no air, no fan. Then, a relay somewhere in the dash starts clicking on and off, and then the climate control comes on. Sometimes I can get it to work sooner by turning the car off, then back on thereby making the relay work again. I remove my climate control panel but to not see any relays, and having just resoldered my climate control cluster last month, I know there are not any relays in there. Any ideas? I think it's just dirty contacts inside the relay, but I don't know where it is.

speedy300Dturbo 12-19-2002 11:10 PM

The clicking noise is the "feedback potentiometer". I know that on a W201, replacement involves removing the dash. Not sure about the process on a 126.

sixto 12-20-2002 03:26 PM

I don't know what a feedback potentiometer is but there's a temperature control unit between the blower housing and the right kick panel.

There's also a blower controller but I don't know where that is.

Are you sure the ACC is completely dead during that time? Could be that the blower isn't kicking in.

91 300SE
87 300SDL
83 300SD

turbodiesel 12-20-2002 03:38 PM


I traced it to that temperature control unit you mention between the passenger kick panel and the blower housing. My blower motor is new so it isn't that and I keep hearing a relay clicking like dirty contacts or cold solders. Thanks for the input.

mpuman 01-06-2003 10:01 AM

A bit late on the reply, but having been there done that, just want to let you know that there are NO relays associated with the climate control. The clicking that you are hearing are the electically controlled vacuum valves (I guess you could call them relays) that control the dampers and such.

The fan is driven by a transistor regulator that provides the varable speed.

I don't know what your problem is (was hopefully), but I can tell you by experence, that without the diagram and service info you most likely are wasting a lot of time (short of replacing the fuses for the hell of it).

Even though the diagram on the CD is very bad, with a little insite you can fill in the lines and track down the problem with your trusty DVM.

- Mike

mplafleur 01-06-2003 02:03 PM

Now that we've broached into the service CD topic, I have to say I've a problem with the quality. It sucks! I looked at the wiring diagrams on my w201 CD and there are black boxes where there ought to be framed boxes with text inside. Half is unreadable and doesn't remotely look like the hard copy I also have.

Years ago when I worked at Ford's Customer Service Division, they were converting their paper manuals to electronic copies for their dealer propietory software. Each worker would scan in a page and then manually edit the bitmap bit-by-bit to correct the page to where it would look exactly like the original. For the money MB wants for those CD's, I'm appalled at the lack of effort to make a quality product. It appears that they took a paper manual and copied each page on the copy machine at the local library without looking at the copy quality of any page. Then they had each of the copied pages scanned and converted to pdf.

sixto 01-06-2003 03:06 PM


Originally posted by mpuman
A bit late on the reply, but having been there done that, just want to let you know that there are NO relays associated with the climate control. The clicking that you are hearing are the electically controlled vacuum valves (I guess you could call them relays) that control the dampers and such.
There might not be relays but something in the SD and SDL makes a 'click' when the blower motor goes down in speed. I don't hear the click in the SE.

91 300SE
87 300SDL
83 300SD

jerryb 01-06-2003 09:48 PM

Mine was clicking when warming up, loud like a 220 relay.
The top electro-vacuum valve to def. was bad, I don't think that little valve could make that much noise, I also tightened the connection for the alarm under the rt. floor and now I have no loud click but if the radio is off and I listen for it I can hear the climate control click as it cycles, but not very loud. It should do nothing until warm enough to blow heat.

BJ300SDL 01-06-2003 10:46 PM

I bought a factory service manual for our 300sdl and it makes that service-cd look like a joke! There are many things they left out of that cd.

sixto 01-07-2003 02:00 AM

There's a bunch of stuff that's not in the index or that the index doesn't point to properly. If you look through the engine folders, you'll see file names with an 'a' suffix. These are typically the versions for turbocharged engines.

e.g., 09-400 and 09-400a (air cleaner), 14-180 and 14-180a (intake manifold), and the list goes on.

91 300SE
87 300SDL
83 300SD

sixto 01-07-2003 02:05 AM


How's the rod-through-the-block project coming along?

91 300SE
87 300SDL
83 300SD

mplafleur 01-07-2003 10:08 AM

It's going to be a summer project; after I build the garage addition. I've ordered the car cover so I can store it up at the old farm (mom's place) till then. I've been told that possibly the block can be reused (welded). I'll take pics of the situation before I tow it away and get some opinions.

Fisherman 01-07-2003 11:00 AM

On the issue of the manuals
I was wondering if anyone had any th9oughts on compiling a Table of Contents for the CDs?

If someone has the actual paper manul they could puit together the TOC and then those of us with CDs could add the pdf numbers to the sections. I know that the one I have for my 115 has more junk on it and cross-referenced stuff that is unnecessary for someone with a 240 but yet you have to search around.
And yes I agree with someone earlier that said that there is much that is not listed. They have the stupidest table of contents on the cd. I mean what the heck is with a title like "Engine Jobs which comprise several design groups"???!!!!
Can't they just say "Oil change, start of delivery, etc..."?
I'm not 100% certain how we would technically pull this together but would love to explore ideas if anyone else is interested?

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