I have done my best to read all of the posts looking for accurate information with regard to my problem. I have owned a 1988 and 1989 560SL, both purchased with 30K miles, that exhibited similar problems. The 1988 was under extended warranty when it needed to have the heat/air box repaired due to a crack. This can be very expensive due to the dash removal.

I live in SoCal and I have a 1989 560SL that I purchased in 9/09 with 30K miles. As of 4/04 it has 60K miles. Lately when I start the car with min A/C on low fan I do not get cold air threw the center vents with most of my cold air going to the defroster vent. This has probably been a problem longer than I can actually remember. The actuators, that open and close vents, have rubber vacuum diaphragms that are effected by Ozone and like any other rubber product will need replacement.

The owners manual says that the center vents are for climate control Normal and Bi-Level for cooling and Economy for ventilation.

I decided to pay my trusted Independent MB repair shop $80 for a A/C vacuum test diagnosis with the following results. There are 7 total vacuum actuators that open and close climate control flaps. Repairing only one is a band aid. My car showed 6 vacuum problems and it was suggested the good actuator be replaced as well. I discussed rebuilding them with $5 replacement diaphragms, www.autoluxmbz.com , http://hvac.mbzarticles.org/vents/permadefrost/ . I decided to go with the repair shops answer to replace due to the age of the car. The actuator housings are made of plastic and may become brittle and can crack due to age.

Here is the bottom line. $960 worth of labor intensive work that requires them to pull the steering wheel with airbag, instrument cluster, and dash to get at all 7 actuators (2 behind glove box, 1 dual diaphragm upper left of radio, 4 in other places ??) that cost $30-45 each. They will also repair the cracked heat/air box that is not opening and closing one of the flaps properly. They also agreed to clean the clear plastic dust on the inside of my instrument cluster. Note: This is a good time to consider a radio change if you want to. I still have my Becker AM/FM cassette that I connect with a cassette adapter to my portable 256MB MP3 player.

In lieu of the $1275 repair I asked them to permanently open the center vents by plugging the line for $40. When I test drove the car I was very satisfied. Now when I set the climate control to Normal I get a fair amount of A/C air to the center and side vents as well as lower vents if I set the car to Bi-Level. I still have a lot of A/C air to the defroster (this is not the way the car was designed but this is the way I drive my Ford because the air is so powerful that I don't always want it pointing straight at me).

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Mit freundlichen Grüßen, Lynn

2000 SL500 Silver
2000 SL500 SOLD
1989 560SL SOLD
1988 560SL SOLD

I did the same with my 85 500sel. Couldn't have been happier with the result. During winter months, you can just turn off the independent vents in the center if you don't feel comfortable with warm air comming out.

Citrus 717