I've never had center vent airflow on my 300SD since I bought it. Found one vacuum pod with a split diaphram. I've patched it and ordered replacement diaphrams. The pod for the center vent works fine with the mityvac.

I put a vacuum gauge on the supply to the vacuum switch network for the climate control and saw 22 in Hg vaacuum. After everything is together, I have no vacuum supplied at all. Where is the vacuum source for the climate control? I suppose there is a tee and a checkvalve somewhere.

__________________
Michael LaFleur

'05 E320 CDI - 86,000 miles
'86 300SDL - 360,000 miles
'85 300SD - 150,000 miles (sold)
'89 190D - 120,000 miles (sold)
'85 300SD - 317,000 miles (sold)
'98 ML320 - 270,000 miles (sold)
'75 300D - 170,000 miles (sold)
'83 Harley Davidson FLTC (Broken again) :-(
'61 Plymouth Valiant - 60k mikes
2004 Papillon (Oliver)
2005 Tzitzu (Griffon)
2009 Welsh Corgi (Buba)

Wish I could be more specific, but I did not see this........My indy completely removed a vacuum filter or valve that was clogged and not letting enough vacuum thru to the climate control or the transmission. Once he did this I had center air and smooth shifts.

They did not replace the part as he said that once these cars get older they do not need it. I took his word for it and so far no ill effects and many positive ones. It was not a big deal and they did not even charge me for it.

BTW, this was on the '87 SDL

__________________
Alan Hamm
'87 300SDL 277K Miles
'89 560 SL 68K Miles

Well, I repositioned my tee's and interconnect hoses and I read 20 in Hg vacuum again. Probably a loose/bad connection.

Next, my real problem is that the controller never actuates the #4 vacuum relay, the one for the center vents. I'll monitor it for a while and if it never turns on, I'll bypass the controller with a switch.

__________________
Michael LaFleur

'05 E320 CDI - 86,000 miles
'86 300SDL - 360,000 miles
'85 300SD - 150,000 miles (sold)
'89 190D - 120,000 miles (sold)
'85 300SD - 317,000 miles (sold)
'98 ML320 - 270,000 miles (sold)
'75 300D - 170,000 miles (sold)
'83 Harley Davidson FLTC (Broken again) :-(
'61 Plymouth Valiant - 60k mikes
2004 Papillon (Oliver)
2005 Tzitzu (Griffon)
2009 Welsh Corgi (Buba)

I have heard a fairly distinctive thunk noise as the flap for the center vents changes. I wonder if you can isolate that vacuum line and get it to do that with vacuum or pressure from a mitivac? If not does that mean that the acutator is bad?

__________________
Alan Hamm
'87 300SDL 277K Miles
'89 560 SL 68K Miles

The center vent should open when using any of the 3 center mode buttons in cooling mode. Maybe you have a problem with the cabin temp sensor or aspirator motor.

Sixto
95 S420
87 300SDL

Hi Alan.....

I also have a 87 SDL - Just curious as to which part was removed???
I'm having some hard shift issues, mainly within the first 5 miles, and some minor climate control issues, like not wanting to shut off (the 'O' button)

Thank You in Advance

Stephen

__________________
98 K2500 Suburban 6.5 Luxo Barge

"We cannot change the wind - But we can adjust our sails"

I have tested both the center vent vacuum pod (above right knee) and the vacuum relay (right side of center console, #4) and both are fine. It is the controller that is not turning on the center vents.

The aspirator motor is working (under far right vent) but can't be sure the temp sensor is working. The small facia plate for the sensor is broken off, so I assume someone else may have had reason to inspect the sensor.

I have removed the push button controller and cleaned and resoldered many of the connections to the relay terminals. Some looked overheated where you could see that the solder had reflowed and the connection to the terminal was suspect. I removed all the solder, cleaned them and resoldered. After that, I had blower motor operation again with temperature control. But no center vents. The center vents have never turned on.

I have noticed that with the temperature wheel all the way cold (A/C condensor cracked, so no A/C) I get cool air at window and floor but sometimes it gets warm or hot. Could this be the sensor?

Is the sensor easy to remove? I just need a replacement part# for Radio Shack, RS Electronics, Allied Electronics, or Digikey.

__________________
Michael LaFleur

'05 E320 CDI - 86,000 miles
'86 300SDL - 360,000 miles
'85 300SD - 150,000 miles (sold)
'89 190D - 120,000 miles (sold)
'85 300SD - 317,000 miles (sold)
'98 ML320 - 270,000 miles (sold)
'75 300D - 170,000 miles (sold)
'83 Harley Davidson FLTC (Broken again) :-(
'61 Plymouth Valiant - 60k mikes
2004 Papillon (Oliver)
2005 Tzitzu (Griffon)
2009 Welsh Corgi (Buba)

I wish I knew and could tell you which part it was. Sorry. If there is a line that just goes to the cabin climate control and transmission before splitting between the two, I would look there.

__________________
Alan Hamm
'87 300SDL 277K Miles
'89 560 SL 68K Miles

Alan.......

Thank You for the reply.

The search continues.

Stephen

__________________
98 K2500 Suburban 6.5 Luxo Barge

"We cannot change the wind - But we can adjust our sails"