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).

[RickM]

Lynn or others,
Is there a particular procedure for "plugging the line". I'd like to have my center vents open all the time as well.

[yeldogt]

Please tell us were the seven are. This would be a great help since it is not covered in the forums

I also know of the problems with the manafolds behind the glove box.

The ACC system on the 560SL is a weak point on the cars -- I would love to find a good overview of the system.

I have spent more money over the years on this system than any other on the car.

So far the unit inside the heater box still works -- but I have fixed many other parts.

Last year when my center vents stopped working it was the single unit to the left of the radio that was bad - the problem is that I could not figure out the system -- I had to take it to the dealer for service.

You can tell if the system is leaking -- the dealer told me to just turn the car off -- if the system still changes the vents after it is sitting for a while than all should be leak free enough to be working correctly.

[lynns]

Originally posted by yeldogt
Please tell us were the seven are.

This picture is from the Model 107 Service Manual Library on CD.

[tan man]

lynns,
it is just typical of MB and many other mechanics to say it is not enough to just change the bad actuator, that you should change all the "suspect" ones and even the good one. sure, throw money and parts at it to keep it working (and them working).
my flaps were not working either. i took the vacuum diagrams, tested all the lines and switchover valves and found 2 problems - a bad check valve and bad center vent actuator. the check valve is causing the system to lose vacuum soon as i turn off the engine. its an easy fix. the center vent actuator looks like it is really tough to get at, i can't figure it out. so i plugged the line leading to it with a golf tee and the rest of the system now works correctly. the center vents lay permanently open
can anyone here please tell me how to get at the center vent actuator? i removed the instrument cluster, radio, center panel that has the pushbutton unit, glove box and lower right side dash cover. i just don't see how that black box for the center vent flap is accesible.
jack

[lynns]

Originally posted by tan man
can anyone here please tell me how to get at the center vent actuator? i removed the instrument cluster, radio, center panel that has the pushbutton unit, glove box and lower right side dash cover. i just don't see how that black box for the center vent flap is accesible.
jack

Thanks to Frank (ftouchton), here is his answer to me on how he was able to do this.

"To get to the defrost accuator you must remove the cigar tray, climate control and the radio. I also recommend removing the console for better access.You do not have to remove the dash. All of the above mentioned items are very easily removed. The actuator is a pain to remove but reassembly is easy. Do a vaccum check on the actuator before removal, if it holds vaccum just replace the lines. Before doing any of the above do a vaccum check of the whole system. It is lot easier to replace a vaccum line than to replace the defrost actuator."

Please see this post: "Center Vents not working...Yes, I know this is a common problem", 07-16-03.

"I just replaced my defrost vent actuator on my 86 560sl. It can be a ***** to get to, I had to remove the console to get to it. The actuator is on the left upper side of the radio. it is a dual actuator that can be removed and repaired or replaced. it has three wiz nuts holding it on the bracket, I broke the actuator removing it. I bought the actuator for my 86 about a year ago and had read that you have remove the dash to service it. to install a new one you have to remove the wiz nuts to get it out or take it apart to replace the diaphram."

"The 107 maintenance manual says to remove the dash to service the actuator, DON"T DO IT. You can get to the actuator thru the center dash openig if you remove the climate control unit, radio and console it is on the upper left of the opening there is a rivet holding the arm to the top of the actuator this has to be drilled out, I used a #10 drill bit. if you get the parts and the tool to disasemble the actuator the new diaphragm should be a snap to change. On my 560 it is a dual actuator so you have two pieces to remove. Make sure the new actuator is seated properly or you will be back where you started. You will have to use a machine screw w/ locknut or a rivet to hold the arm on the actuator, don't over tighten or it may bind up. Putting everything back together is a snap. I did mine last week, so if you need any guidance let me know."

[yeldogt]

Tan man:

If the center vents are not opening (they default closed - w/no vac) you could have no vac going to it or the unit could be bad -- they only way to tell is to hook a line to it (it sounds like you did this). If that is the case than it is a big job - the unit is inside the heater box -- why I do not know -- this is a very bad design.

I also do not understand how you can plug the line to make it work since it only will open the vents if it has vac?? If it opens it is working??


In my case the center vents were not getting vac -- so they would not open. It was the unit for the defroster -- this is the one located behind and to the left of the radio. this is a two position unit -- partial when you want to have air at the window and at you feet -- all the way when in defrost mode.

I am not sure what was bad on the unit -- was about 65.00 -- total cost was around 400.00

The new unit was a little larger and looked much stronger than the original.

All the other units are original - I was luckey it was not the center unit

[tan man]

yeldogt,
i traced the vacuum leak to the center vent actuator. so i plugged that vacuum feed line. which stopped my vacuum loss and allowed the rest of the system to work properly.
for the center vent flap, when i applied vacuum there was no resistance at all so the center flaps did not budge. the only part of the actuator that i could see is the little nipple that the vacuum line attaches too. that little nipple to the center vent actuator moves around so i think the whole diaphragm is loose. i poked a screw driver thru one of the vent opennings and manually openned the center vent flaps - they stayed open. . how is someone supposed to get at that actuator inside the heater box!!!?? was the whole car built around that little thing?

[lynns]

Originally posted by tan man
lynns,
it is just typical of MB and many other mechanics to say it is not enough to just change the bad actuator, that you should change all the "suspect" ones and even the good one. sure, throw money and parts at it to keep it working (and them working).
my flaps were not working either.
jack

I bought my '89 560SL in 9/99 with 30K mile. Since that time I have had to replace various plastic and rubber parts. IMHO this is due to age, environmental factors (heat and ozone), and everday wear and tear. The car now has 60K miles as of 4/04.

$850 OE radiator by Behr due to cracked "plastic" neck on the influent to the radiator.

$615 "rubber" subframe and motor mounts.

$159 valve cover "rubber" gaskets.

$57 "rubber" exhaust hangers.

With regard to the 7 actuator "rubber" diaphragms. I have a choice to repair one, all, or none. Don't forget that if you choose to do them all the dash will need to be removed and the heater box probably repaired. approx cost $1300.00

[ljmauricio]

Tan Man, can you elaborate on how you used a screwdriver to open the center vent flaps. I would be happy to have the vents permanently open. Thanks

[RickM]

OK, found it. Here's the best thread I've found on opening the center vents.... propped the center vents' door open

[ljmauricio]

Just thinking out loud here. My center vents are not working and somewhere in this thread has suggested propping it open thru the center vents. I've tried this by using a long handle screwdriver thru the middle vent and pushing against the bottom of the flap. It opens easily and air immediately comes thru. Haven't done this yet, but would seem a very simple matter to make a small wooden wedge that could be pushed in thru the center vent and left there. The further you push the wedge, to wider the flap opens. Make it long enough that you can reach it with long needle nose pliers in case you ever want to remove it. No need to take anything apart.

[RickM]

I'm guessing you read the link I posted? ?????

[ljmauricio]

RickM, as I mentioned the wedge idea came from somewhere in this thread. Thanks!

[Strife]

I picked up a vacuum pump kit from harbor freight for $30, and I've just completed some individual diagnostics on my vacuum pods (pump already paid for itself bleeding my brakes). My 4 outside air pods are good, the center door unit is good (!), but the defroster unit is NOT (I didn't check the heater box). My 1986 (560) supplement to the shop manual (different than the diagram previously shown) shows that this unit is dual; apparently, the lower part contributes to it's operation, and the vacuum for the upper part is shared with the center door. Therefore, if the upper part of the defroster vacuum actuator is leaky, no vacuum will get to the center door. Well, the good news is this one is a lot easier to get to, the bad news is that I will have to drill out a rivet. I have plenty of neoprene diaphragms and the tool, so there is definitely a remote possibility that I can have this working this weekend!

I think someone mentioned that they had their defroster unit replaced by MB with a slightly larger unit; I wonder if the one I have installed was underdesigned.