Rear Head Rest wont go down 1991 300E
 

Just bought a 1991 300E. Both of the head rests do not go down on the rear bench seat. The vacume system works for the door locks. Are the head rests on a vacume system? I see a button on the dash with what looks like a head rest picture but it does not activate them. Thanks
JRR

Do you have an owner's manual? That would tell you what switches are where. Can you hear motors working when you hit the switch? If not check fusebox, and then try swapping a window switch out for the switch you think operates the headrests. The headrests are electric, and most of the switches in the car are simple mechanical rocker type switches and unless the pins are keyed differently they should interchange. If not and I'm totally wrong try to power them somehow with 12v at the plug end behind the switch to see if the motors and gear drives are functional. Should tell you whether it's the switch or the motor/mechanism.

Head Rests
 

Thanks for the tip. Now that I know they are mechanical I know where to look. I am having a fuse box issue. It partially melted so I have anew replacement ready to go in as soon as we get a day over 35 degrees!
JRR

The engine has to be running for the rear seat headrests to go down with the dash switch.

I have a 91 300E. I guess I could be wrong, as I've never had a close look at them, but I was always under the impression that the rear head rest release was vacuum actuated.

my bad - I was talking about the fronts.

??? I may be wrong then
 

read this
http://www.benzworld.org/forums/w140-s-class/1490003-pneumatic-rear-headrests-wont-drop-down.html

I always thought they were powered, like the front headrests. ???

head rest
 

The fronts are definately electrical. Still not sure about the rear though! Just installed the new fuse box. Hope this helps and gets a few things working!

Electrical Switch "Trips" Vacuum Release.
 

Non-Critical System...
'Love those German engineers!

The rear headrests on the 300E are dropped by an electrically actuated vacuum solenoid. It opens and allows vacuum to the headrest mechanism. They then release/fall back.

Aha! I wasn't wrong I just wasn't right.

Rear Head Rest wont go down
 

OK so now that I know it is both electric and vacume what do I look for to fix it? Like I said the door lock are working so I assume a leak is not the issue. JR

Look Here
 

Wonder why they put that on the E-class and not the S-class of the same era?

The vacuum supply for the rear headrests comes directly from the engine with no check valves or reservoirs so the engine has to be running for the headrests to get vacuum. The door lock system is separate with a vacuum pump.

There is a valve under the rear seat bottom on the left hand side for the headrests. There are two vacuum lines, one from the engine and the other continuing to the vacuum pods on each headrest mechanism. The module has 12 volt power, ground and 12 volts when the console switch is pushed.

Pull the white vacuum line off and with the engine running, see if there is vacuum present. Pull the white/blue line and connect to the white line to see if the headrests drop. If they do, check for an electrical/valve problem.