SL500 air vent problem


Asked by Scottc Jul 13, 2007 at 12:37 PM about the 1999 Mercedes-Benz SL-Class SL 500

Question type: Maintenance & Repair

My 1999 SL500 has recently stopped blowing air out of the  foot vent and the center vents of the system. Air and Heat still come out of the defroster and side vents. (the settings for the center and foot vents are set properly) What could be the problem?
Thanks Scott

13 Answers


You may have seperate blower motors for different vents. You could also check your fuses to see if one has blown.

5 people found this helpful.

Yeah, checked all the fuses, the Climate control unit responds well including diagnostics, it even registers the vents opening and closing when I do it manually with a screwdriver. I'm inclined to think it may be the Vacuum Valve actuator. which is what I am afraid of.

2 people found this helpful.

This turned out to be a disconnected Vacuum hose behind the firewall. Once I located the loose connection (small thin white tube) and connected back to the engine hose. Vents began to work after I started the engine and ran for few minutes.

24 people found this helpful.

Scottc, I have the identical problem with my 99. Could you be a bit more specific as to the location of the thin white tube? Thanks

58 people found this helpful.

Glad you found it, probably saved yourself $200....I'm re-doing my convertible top in the next couple of weeks (getting all the parts and tools together), can't see paying someone $2k to do a lousy job (got the top on Ebay, and an installation video) looks easy but tedious, lets see how it goes...

4 people found this helpful.

Knowing my local M-B shop, I think it saved me a lot more than $200. Let us know how the top installation goes. Have a great summer, thanks again.

2 people found this helpful.

I have the same problem, connected white hose, ran a few minutes then stopped, any ideas?

6 people found this helpful.

I also have 99 sl500, can you please let me know where the white tube is?

11 people found this helpful.

Where was the hosecond located? Do I need to remove console? Other feeds said sensor or control module. Fuse box under hood is fine but I also,read there are 3 boxes where are they?

8 people found this helpful.

This issue is normally due to a vacuum leak, like a loose vacuum line, but the most common leak is a split on the underside of the Vacuum Distribution Block. It is located near the firewall.. you'll need to remove the large flat cover to get to it. On the underside of the block, there is a ball bearing that works as a seal, check for a split/crack here. Reseal with epoxy or similar. Or just buy a new block: 1478.htm?pn=129-800-14-78-M22

1 people found this helpful.

Thanks, fixed it in 1 minute. In case anyone is trying to locate it: the small white hose is the diameter of a swizzle stick located almost in the center coming out of firewall accessible from drivers side; connects to black hose.

3 people found this helpful.

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