1981 mercedes 380sl climate control - PeachParts Mercedes-Benz Forum

dima4855 · #1 02-21-2006, 03:51 AM

Greetings,
I just bought a 1981 mercedes benz 380 sl and having issues with the climate control.
Heater:
when I turn the temp wheel to 85 with the ac switch on off and hit auto lo or auto hi, no heat comes out, blower doesen't blow. I can turn on ac switch and turn it off and then cold air starts blowing, but only cold air and it is blowing everywhere except for the three vents in the center. Defrost and bilevel also blow cold air.
A/C:
A/C works and cools fine except no air comes out from the three center vents.

What I've done to troubleshoot:
1. Tapped on the climate control servo in the engine compartment (it stamped manufactured in USA). Checked all vacuum line.
2. Check and replaced the fuse in the passenger compartment.
3. Pulled off the center console and double check all wiring (to my best abilities).
4. Checked the vaccum line on the driver compartment, even unplugged everything and had the green hose go direct to the intake. Still same problem.
5. There is a clicking noise coming from what appears to be a cylinder thingy at the foot of the passenger compartment. Mounted on the firewall.
There is three of those things in a row with what appears to be a vacuum line coming out of it.

mbdoc · #2 02-21-2006, 09:25 AM

IF you can't get heat in DEFROST then the servo is the most likely problem.

Check out the ad in the SL forum for un-wired tools.. they have a kit to by-pass you old non-functioning servo.

dima4855 · #3 02-22-2006, 02:01 AM

but isn't true that if the servo was bad I would get cold air blowing out of the vents with the ac off and the temp set to 85?
In addition, if that was the case how can I bypass the servo with a mechinical vaccum pump.
I thought the bad part would be the valve/butterfly that opens up the heater/outside air vent?
I will check out the post in the sl gallery.
Thanks bunches.
Dmtiri

Richard Wooldridge · #4 02-22-2006, 10:19 AM

Hi there,
If your blower won't run in the auto-lo or auto-hi positions there isn't enough vacuum to operate the "main" vacuum switch. It's the one with the green body. It requires around 10" of vacuum to operate, and is in series with the blower motor. Usually there is a leaky diaghram on one of the air flap controls. My car had a plugged check valve under the engine hood that was obstructing the vacuum to the heater. If you cannot get heat in the defrost position, the servo unit under the hood is most likely also bad. As MB Doc says, check out the unwired tools servo upgrade, it is the best way to go if you are going to keep the car. The original servo units are unreliable and very troublesome, and can cause your battery to run down if they jam in the wrong position. You can go to the unwired tools web site and download their vacuum diaghrams, which are very helpful in locating vacuum leaks.

dima4855 · #5 02-22-2006, 07:07 PM

where is this main vacuum switch?

Richard Wooldridge · #6 02-22-2006, 08:32 PM

On my 450SL it was behind the glove box liner. I could see it from underneath, but it was easier to see by removing the glove box liner. It was the one farthest to the right (passenger) side on my 450SL. On my 450SL there were 7 or 8 vacuum switches/controls behind the glovebox.