Hello. I’m a new member and new owner of a 81 300sd. It’s a great old classsic car but im having some issues with the climate control. So the the big thing is regardless of which button is pushed i only get air from the the defrost vents and some from the footwell area. The air is mostly cold the odd time it will be Luke warm at best. So doing some digging i may more than one issue possibly from a bad mono valve to the vacuum pods and vacuum actuators. The vacuum line that feeds the system does not have any vacuum when i have my mighty vac hooked to it. Also i have noticed that there some oily type of residue present on the hose as well as on the the row of vacuum actuator at the connectors. I hoping if some has some direction or advise in which order i should proceed with the repairs. Also if there some info ie wring or vacuum diagrams . That would be great. Thanks in advance.

Start with the basics:
Fuses F10 (control) and F11 (power)
Then go to the most common component: The pushbutton controller
On mine, and most reported here, the internal circuit boards had cracked solder joints. This is due to the boards arranged in an "H" and over time the solder cracks where they meet. A search of "resolder pushbutton controller" will likely give you pictures of the areas I'm talking about. If you aren't comfortable with resoldering, there are others here who can do it or remanufactured units are available.

Usually a vacuum pod problem is when the system doesn't direct the heating/cooling to a particular vent but not all of them. Defrost and heat are the defaults.

Bottom line, the "defrost only" is likely to be the Pushbutton Controller and "no heat" is likely to be the mono-valve.

Here are some diagrams to help you out:
https://www.startekinfo.com/StarTek/outside/12253/program/ETM/81etm.pdf
https://www.startekinfo.com/StarTek/outside/12253/program/Climate/83-604.pdf
https://www.startekinfo.com/StarTek/outside/12253/program/matrix.htm

__________________
Sam

84 300SD 350K+ miles ( Blue Belle )

Thanks SD Blue. I’m hoping to dig into the car again in the next day or to.

So i had a look at the Benz today. Both fuse 10 and 11 have power. With the vehicle running have power to one of the pins at the connector for the mono valve. I also removed the valve to inspect the condition of the rubber seals. The seal are not torn. I did check the aux pump connector and have no power at either pin. I did remove the cover for the control unit. It appears that the unit has the solder redone. While the vehicle is running my vacuum line has zero vacuum. Under the hood i have a feed line that splits to two lines. Brown line and the red with white stripe line that goes to supply the vacuum pods. When i disconnect the brown vacuum line and plug off the end then i get 15 inches on the red with white stripe line that goes to the vacuum pods. Does any one know what the brown vacuum line feeds? I will try to added some pictures. I did at a picture of a connector that im not sure what it plugs into. It is located in the center console area around where the radio would be.

Attached Thumbnails

   

I believe the brown vacuum lines are for engine shut-down. Are you having any issues in that area?

Mono-valve is tied directly to the fuse so it should have constant power. MB switches the ground side for control. Mine has stuck closed in the past so that may be the problem with it. It should default to full heat when disconnected, I believe.

That connector may be for the power antenna or fader, I'm not sure.

__________________
Sam

84 300SD 350K+ miles ( Blue Belle )

SD Blue. I haven’t had any issues with vehicle shutting off when turn the key off. Within 5 seconds the car shuts off i would say. But something was bothering in regards to the vacuum because when i disconnect the brown supply tube and plug it off i get vacuum at the supply tube to the climate control pods.since i had the lower dash trim and center console out i wanted to try to look to see if i could see any odd. All though i could see the red supply tube tucked up in the dash i could not see the brown tube. Since the lower trim was out i stuck my arm under the dash , reached up and pushed out the instrument cluster. I gently pulled the cluster forward to i could have a look at where the lines are going. I knew there should be some lines going to the ignition switch. With the cluster forward i could see the switch thru the opening. The switch looked clean no oil stains. So I started the car with my vacuum gauge hook to the red supply line for the climate control in the car. At first there was no reading on the gauge . When i pinched the rubber portion of the brown supply hose from the vacuum pump to cut . Right away the vacuum gauge when to 15 -17 inches of vacuum. When I released the hose the gauge went back to 0. So i tried to pinch the other brown with blue stripe tube going back to the shut off valve at the engine. Again the gauge reads 0. So now im wondering in the is the vacuum switch faulty or is there a chance that the hoses have been installed backwards. I didn’t get a chance to swap the hoses but this is way it is set up right now. The supply brown line from the vacuum pump is connected to the nipple next to the ignition switch body and the brown hose with the blue stripe going to the shut off valve is on the nipple furthest away from the ignition switch body.

I'd suspect you have the vacuum lines backwards at the key switch. With the key in "run", the nipple going to the shutoff pod on the injection pump is vented to atmosphere. If you have the lines backwards, you'll be venting the vacuum source to atmosphere - a true vacuum leak.

The other clue is that you have nearly good vacuum (20" or better is normal), but the shutdown is slow. When you turn the key, it should be immediate - 5 seconds is way too long.

__________________
Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

Hi guys just an update. The vacuum lines that came into the shut off at the ignition switch where installed the wrong way. The supply line was hooked to the vent side of the valve so it was always venting the vacuum when the vehicle was running. That was the reason I wasn’t getting vacuum to the climate control. I’m really happy that the climate control now appears to be working properly. I’m still learning how and what is opening and closing when i push the different buttons on the control unit. Thanks for the advice.

Thank you for posting the solution. Many times a newbie shows up with a problem, gets a variety of responses and forgets to resolve the thread by posting the results of his experiments to let everyone know how the issue was resolved.

The minds of the men here are a database of the finest accumulation of Mercedes Diesel knowledge in the world but they are still human and have enough humanity to appreciate being acknowledged and thanked for their time and advice.

__________________
84 300SD
85 380SE
83 528e
95 318ic

Glad you got it sorted out. It's a nice system once you get it working.
Too many give up and jury rig a bunch of hokey switches or pinning the air exchange doors. This usually takes longer than fixing it correctly.