center vents not working on 560SL

[lynns]

I have done my best to read all of the of posts looking for accurate information with regard to my problem. I have owned a 1988 and 1989 560SL, both purchased with 30-35K miles, that exhibited similar problems. The 1988 was under extended warranty when it needed to have the heater 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 9/99 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 vacuum elements (actuators), that open and close vents, have rubber diaphragms that are effected by Ozone and age 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 elements (actuators) that open and close climate control flaps. Repairing only the center one, located next to the left side of the radio and the two behind the glove box, is a band aid. My car showed 6 vacuum problems and it was suggested the one good element 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 suggestion to "replace" due to the age of the car. The actuator housings are made of plastic and may become brittle and crack due to age.

Here is the bottom line. $960 worth of intensive labor that requires them to pull the steering wheel with airbag, instrument cluster, and dash to get at all 7 elements that cost $30-45 each. They will also repair the cracked heater box that is not allowing the center vent to open and close and causes an in the dash rattle when I go over certain road surfaces. Note: This is also a good time to consider a radio change if you want to. I have chosen to keep the factory Becker AM/FM cassette that I occasionally connect with a cassette adapter to my portable MP3 player. This car had speaker upgrades with two 6x9's in the rear, tweeters in the door pockets, and I believe upgrades in the dash speakers. Sounds good enough for me !

In lieu of the $1275 repair I asked them to permanently open the center vents by plugging the line for $40. (BTW, they where able to do this easily because I had already removed my glovebox.)

When I test drove the car I was 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).