I've finally had it with the CA weather and decided to try and sort out the A/C issues with my 300sdl. I've had the car for about 5 years and almost all maintenance has been performed on schedule. I say almost, because the A/C is the only thing that's been neglected. When I bought the car, the A/C blew moderately cold. However, the center vents would work erratically and then the system would shift to defrost mode; at that point the mediocre A/C would no longer cool the cabin. This wasn't an issue because I've always had a second car with working A/C so on really hot days I just wouldn't drive it.

Well my second car's A/C is now out of commission, so while I get the funds together to have the entire system rebuilt, I'd like to at least see if there's an easy fix for the SDL's center vents so I can also have this A/C charged. It really annoys me that the MB engineers designed such a convoluted and overly complex ACC for these cars in U.S. trim.

Is there a simple way (without removing dash) for me to rig the system so that the center vents are always open? Down in SoCal we hardly ever need defrost. Thanks!

__________________
"Time's never wasted when you're wasted all the time"

The first thing to determine is whether the pod that operates the center vent is functional. This can be done by gaining access to the six switches that control the vacuum to the pods. These switches reside directly next to the radio and can be accessed by removing the kick panel, carpeting, and the carpeting on the tunnel on the passenger side. Once the switches are exposed, you can disconnect vacuum to each switch (the horizontal leg) and use a Mityvac to check the pods. From memory, the center vent pod is one of the switches in the middle of the row. I can check it on Monday for the exact switch. If the pod holds vacuum, the center vents will now be open and air should be flowing from them. If the pod will not hold vacuum, you're faced with the difficult job of replacing that pod. It's not completely impossible on the W126 without removing the dash but requires some dexterity and some clever tools. I have not done it myself, however it has been done by others.

That's a good amount of the answer. If the defrost pods are shot, and it sounds like they are if air blows from the defrost vents when the center vents quit, you'll have to address those as well to have a good volume of air through the center vents. I know it's possible to wedge the defrost vents closed without pulling the dash. Hopefully you don't have a passenger side airbag. Pulling the glove box liner gives you access to the defrost and recirculation pods. I think you can wedge the center vent open though the cavity exposed when you pull the ACC PBU. If not, pulling the dash doesn't help very much until you remove the airbox

Sixto
87 300D

Thanks for the responses Clarence & Sixto. BTW, mine doesn't have a passenger side airbag. I will hopefully get to it sometime during this week once I'm done changing the compressor on my BMW. It really bothers me that the only time I truly get to enjoy the SDL is from fall through spring because of this crappy ACC. With this indefinite heat wave it seems like I might not get drive her at all unless I address this issue.

__________________
"Time's never wasted when you're wasted all the time"