View of 107 ACC Modules
 

I am trying to get the ACC on my 560SL to do something besides blow hot air at the windshield. So I working with the glove box out testing the vacuum actuators, and I thought I would post this picture of the key components of the ACC system., since they don't exactly stand up and introduce themselves.

This is looking in through the glove box.

1 - vacuum distribution module. Receives commands from the push-button unit and sends vacuum to appropriate actuators to open and close flaps. In the 380's this is 4 electro/vacuum switches mounted more to the right.

To get to this unit, you need to remove the stereo's amplifier CORRECTION - it's actually the alarm module (see below), which is normally mounted right in front of it.

2. - blower module. Takes input from the blower buttons and temp wheel and sensors and figures out the correct fan speed (black)

3. - temperature control module. Reads the dash and heater box sensors and temp wheel setting, and sends ground (close) to the monovalve to regulate hot water flow to the heater core (silver). The blower module mounts directly in front of it, and must be moved for access, as it has in the picture.

There is no stereo amplifier unless you put one in. It's most likely the ararm module you removed.

John Roncallo

I will check this tonight. I thought it said something about radio/stereo, but then, a senior moment can strike at any time. It lies flat and attaches to the top of the large plastic air vent. Wiring and connector looked completely original.

I know in the 450 that would have been the amplifier for the stock stereo. Not that that's much help, but....

yup... on my '88 560, the module is the alarm. Toss it if you wish.

http://www.peachparts.com/shopforum/1330130-post12.html

See the link above for a clearer picture of everything under there. Hopefully you wont have to go as deep. I belive your problem is most likely the center actuator shown in one of the pictures in the link. Some say this can be done without removing the dash. I never tried it because on both my cars I had to replace actuaters inside the heater box anyway. Note the rivets on the heater box just to the right of the defrost actuator. That is wher the heater boxes tend to crack.

If you do have to pull your dash do a serch in this forum on "center vents" or "center vents not working" or "Will Sadie ever run again"

You will get plenty of info on pulling dashes, repairing heater boxes and changing vacume actuators for both center vents, defrost vents and legroom actuators.

John Roncallo

Please read http://www.peachparts.com/shopforum/mercedes-benz-sl-discussion-forum/90889-center-vents-not-working-560sl-post1238486.html#post1238486

Well, it was a semi-senior moment. The module in question does say "Becker Auto Radio" on it, so I assumed it was stereo-related.

WRT the problem. All of the actuators are holding vacuum. The vacuum controller is distributing vacuum correctly when the buttons are pushed on the control unit. But the mounting of the flaps in the heater box has broken out around the rivets. I got it back into position and am going to try a repair with a large amount of JB Weld. See picture for start of repair.

Another issue is that the dash temp sensor is TU - as in open circuit. I picked up the new part this morning, so maybe with some beter input the temp control unit will start doing something.

Stay tuned.

You might wish to navigate to http://users.adelphia.net/~rmsmithco and follow the links for a couple of ideas...

You know I forgot all about that web sight. It's going to help allot of people. I'm glad I had a small part in it.

John Roncallo

Mostly back together with the new in-dash sensor and sort-of-repaired heater box. Good news is that there is better air control - less going to the windshield, a faint trickle to the footwells, the center vents move, and the recirculate switch seems to work.

Bad news is that there's still no temperature control. So I need to figure out how to test the resistance reading at the heat control module, and if that's OK, replace the module.

Thanks to the guys for all the suggestions and links - this is the forum at its best!

your input was very welcome, and invaluable...
Now, Lets see some more of that 12-pot beast!

I continued to investigate my 560's always-on heat. I took resistance readings from the two sensors and the temp wheel. The readings from the sensors were in spec. But the readings from the temp wheel were odd:

MIN - 1.31 k ohms, spec is 1.6 k
22 deg - 5.14 k ohms, spec is 3.15 k
26 deg - 8.6 k ohms, no spec
MAX - 8.1 k ohms, spec is 1.6 k ???

My questions:

Is the MAX reading a misprint? How can low and high temp have the same reading?

Are these readings far enough out to justify a replacement of the wheel?

FWIW, here's what's behind the 380 Glove box. Actuators are disconnected for the pic.

http://www.peachparts.com/shopforum/...6&d=1190813719

I've got the printed version of the ACC manual and I just checked it.

MIN (engaged) 1.6K ohm
22C 3.15K ohm
MAX (engaged) 1.6K ohm

and the recommended resolution if the values are off is to connect a new temperature wheel.