1. My air vents seem permanently stuck in the "put everything on the windshield" mode. The center vents get no air conditioning and no heat. It all gets defrosted.

Is this the "monovalve"? Is this a "dashpot"? What is my problem?

2. My back vent dispenses hot outside air in the summer, cold outside air in the winter. I know it's an odd part of the car... based on that information, does anything require repair?

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~Michael S.~
Past cars:

1986 300SDL
1987 300SDL
1982 240D
1982 300SD


Current:

1987 300SDL

1. Sounds like you have some vac leaks in the climate control system. Use your mity vac and test all the pink actuator pods under the dash. There are 5. One directly behind the center vents, two behind the glove box(one on each side), one directly behind the center console just above the floor(you have to stand on your head, with your head stuck down in the foot wells to see this one), and one in the drivers foot well on the right hand side. When you hook up your mity vac, pump it a few times. The pod should actuate AND hold vac. If it doesn't do both then it's shot. New diaphragms can be put in and it's a lot cheaper that way than buying a whole new pod. I replaced all the diaphragms for the price of one new pod.

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I'm sorry for the stupid question. But one of my majorest automotive weak spots is figuring out how to do things like getting behind door skins and glove boxes and radios. I'm terrible at it.

How do I get 'behind the center vents'?
Behind the glove box?
Behind the console?

(The footwells I know how to do)

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~Michael S.~
Past cars:

1986 300SDL
1987 300SDL
1982 240D
1982 300SD


Current:

1987 300SDL

Again I didn't read your signature. So my diagnosis may not work for you. I assumed you had a 123. In the 123's you can pull the glove box out by pulling the center part of the plastic tabs in the box. Then pulling the rest of the plastic tab out. Along with disconnecting the light. And the box pulls out. Then you should be able to see what's going on back there.

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OK, I'll try to get back in there somehow. it may be easier than I think

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~Michael S.~
Past cars:

1986 300SDL
1987 300SDL
1982 240D
1982 300SD


Current:

1987 300SDL

You first need to test the system. This is done by removing the right side carpeting and cover from the transmission tunnel. Of course, the right side kick panel and the right side floor carpeting must be removed first. Once you gently bend the carpeted panel, you can remove it without removing the console.

Now, you'll see a row of six vacuum control switches next to the radio. These will operate the six pods in the system. The horizontal leg of the switch goes to the pod. Connect a Mityvac to the hose that leads to the horizontal leg and see if it holds vacuum. Depending on which one's don't hold vacuum........you'll need to locate and replace those.

The best thing is to test all six lines and report back as to which hold vacuum and which don't. We'll go from there. #1 is at the top.

I'm doing that as we speak.

Uh... what do I do if mine has seven? It's obviously designed to have seven, I see the little box with the fittings and they're stickered and color coded so I know which is which.

I started at the bottom since I could get to it, i'm having trouble working my fingers in to disconnect them carefully (the lines are as brittle as the others in the car, which means there will be broken lines before this is over no matter how careful I am)

Number 7 won't hold vacuum and I stopped there to come ask what was going on.

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~Michael S.~
Past cars:

1986 300SDL
1987 300SDL
1982 240D
1982 300SD


Current:

1987 300SDL

Yep......the SDL's have seven........I must have been sleeping........the SD has six.

Unscrew the bracket with the seven switches from the vehicle body. There is a screw at the top, IIRC. You'll never get to all those hoses if you don't.

82 MB 300SD

I am having the same problem with the A/C only coming out of the defroster vents and I'm going to do the vacuum testing, but I also am going to replace the vacuum tubing for the system. Does anyone know the I/D and O/D so that I can order it?

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1987 MB 190E 2.3 16V- Name Pending
1982 MB 300SD -Old Blue
1965 Ford Mustang - Laura

The plastic vacuum tubing (known as Tecalan line) can be purchased from the dealer or from Phil at Fastlane (right on this forum). Press the "buy parts" tab at the top of the page and call him on the telephone.

Thanks Brian. I'm going to cal Phill for the lines. I'd like to order some for the repair and some for extra. You never know when it will come in handy.

I was checking out taking the carpeting out and such and I happened to glance up, (I had the glove box out to facilitate checking the blower motor and such when I was changing and testing the Climate Control Unit which was bad.), and I noticed that the vacuum element that controls the center consoles flap was not hooked up and the lines were capped off. I took it out and low and behold the diaphram was burst.

I want to either replace the diaphram as was mentioned earlier by Biodiesel 300TD in this post or get a new vacuum element. How would I go about getting the new diaphrams and installing them?

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1987 MB 190E 2.3 16V- Name Pending
1982 MB 300SD -Old Blue
1965 Ford Mustang - Laura

You really should not replace the diaphragm on the dual units. The replacement is different than the original and it fits over the top of the original. It's got less travel due to this arrangement.

The duals should be replaced.