I have a 1984 300d and my AC only blows out the side vents and defrost regardless of what button is pressed.

I read this link about the actuators.
PeachPartsWiki: Replacing the HVAC Vacuum Actuators

Before I start ripping the dash apart, is there a way to test the pods that are located behind the ACC? I have some spares from another vehicle that I could use but I'm not sure how to test them.

Does this problem sound like a vacuum actuator problem or a pod problem or both?

It's a lot easier accessing the pods so if there's an easy way to test them, please let me know.

Thx

pete

"pods" "actuators" "elements"... converts vacuum pressure to mechanical force that moves the flaps that control the air flow. They're called "elements" in the catalog.

the only one you cant really reach with out major disassemble is the center vents. just wriggle you way underneath there and disconnect and test each with your mityvac. careful not to over pump them and damage them. Check all the connections and hoses while you're at it.

If those check out then you're gonna have to search on... Take the glovebox out---> the knee panels---> the center console. All of that is way easier to get out of the way that the actual "dash" itself and that will give you access to the majority of the system.

__________________
Current fleet
2006 E320 CDI
1992 300D - 5speed manual swapped

former members
1984 300D "Blues Mobile"

1978 300CD "El Toro"

Most likely a bad vacuum pod diaphragm as that is common but switchover valves control the pods. There's an array of switchover valves behind the ACC control panel. Each can be tested by seeing if it appropriately routes vacuum to the pod when activated.

__________________
1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

Is the attached picture a switchover valve?

When you say "bad vacuum pod diaphragm" is that the same as the vacuum actuators in this link?
PeachPartsWiki: Replacing the HVAC Vacuum Actuators

Thx

Pete

Attached Thumbnails

 

Yes. The diaphragms are inside the 'actuators' or 'elements'. Some diaphragms can be replaced instead of replacing the whole expensive actuator. Search on 'George Murphy' on this forum. He sells the diaphragms.

You can also avoid the whole troubleshooting/replacement work by wedging open the center vents all the time and controlling them via the twist shut off nozzles. That's what I did with mine. Just reached around and stuck a piece of flat aluminum stock into the plenum to hold the flaps open and put a 'hook' on the end of the stock so it hangs on the edge of the plenum, then pulled the rubber boot down around it. I think I described that fix on here in an old post from 2002 or 3.

__________________
1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

Thanks. Did you pull the glove box out to access the center vent?
Is that what you are referring to when you state that you "Just reached around and stuck a piece of flat aluminum stock into the plenum"?

Thx

pete