Master Vaccum Switch/Door locks - PeachParts Mercedes-Benz Forum

mgcanuck · #1 05-27-2008, 01:31 PM

I'm trying to diagnose my door lock vacuum problems. New check valve in engine compartment. The lines and actuators all work and hold vacuum (when tested after the master switch in the door). However, the master switch itself seems to be leaking.

Can someone verify proper operation of this valve? It seems that on locking, it holds vacuum, and unlocking it dumps all the vacuum (or the other way around). I can hear a *swish* as the vacuum is released. Is this correct? It seems it only holds vacuum when the pin is absolutely seated in the switch. It might also be the check valve that is in-line on the vacuum line to the switch itself? I have tested that valve and it seems to leak when i plug it with a golf tee, though not when i put my thumb over it...Argggh....

pizzachef · #2 05-27-2008, 04:56 PM

When you hear the *swish* its probably the vacuum rushing from the reserve tank into the unlock (or lock, whichever state you're moving to) circuit. But if there was a leak at the main switch, you'd probably hear a constant hiss that gradually falls off as your vacuum reserve depletes.

The master valve in the driver's door should hold vacuum for which ever position its in, so if the knob is down, the port leading to the 'lock' circuit should hold vacuum (with the common port plugged) and vice versa. If the check valve is leaking, you'd lose all your vacuum once the engine is shut off, even if you never move the master switch.

If you lose vacuum when you unlock, it may be one of the rubber boots on one of the door elements...I had a couple that had disintegrated. But you said you just replaced all your actuators...maybe test them individually at the vac lines under the floor mats?

mgcanuck · #3 05-27-2008, 06:06 PM

Hey thanks...just to clarify. I did all my testing with a MityVac at the door. So i know all the lines/actuators work because i can make them go/stay up or down this way. However, when i test the switch itself, it hisses off vacuum as soon as the pin is pulled out (door unlocked i think). It makes sense to me it should be a closed vacuum circuit--ie, that vacuum is just routed to the lock/unlock lines with no loss. Must be the switch!

pizzachef · #4 05-27-2008, 06:42 PM

Yup, its just a 3-way valve, one common port in the middle and two "selected" ports. When the knob is up, the common port is connected to one port, when the knob is down, the common port is connected to the other.

I actually bought one when I thought mine was bad, and mine turned out to be good, and the one I bought was the wrong one for my car anyway. I don't remember if its the black one or the white one (its probably the white one since that ones a good bit cheaper and I didnt know any better at the time), but if its the one you need, you can have it for the cost of shipping. I'll post an update when I find it.

mgcanuck · #5 05-27-2008, 08:21 PM

Hey! Awesome...let me know, thanks a bunch!

tangofox007 · #6 05-27-2008, 08:49 PM

Quote:

Originally Posted by mgcanuck

It makes sense to me it should be a closed vacuum circuit--ie, that vacuum is just routed to the lock/unlock lines with no loss.

No, it's not a closed system. Each actuation reduces the vacuum level in the reservoir. If the lock circuit is under vacuum, the unlock circuit is vented to the atmosphere, and vice versa. In reality, the work is being done by atmospheric pressure, not vacuum.

mgcanuck · #7 05-28-2008, 03:06 AM

so where is the loss in my system then? If vacuum is required to raise the door buttons, then venting to atmosphere as you say should make them go back down, no? Not happening.....and this is all with hand-pump vacuum.

tangofox007 · #8 05-28-2008, 10:04 AM

Quote:

Originally Posted by mgcanuck

If vacuum is required to raise the door buttons, then venting to atmosphere as you say should make them go back down, no?

No. The door lock actuators are not spring loaded to one or the other position. They require vacuum to move in both directions. The switch basically connects the vacuum reservoir to either the lock or unlock side of the actuator. And vents the opposide side.

If you think it, I suspect that it will become very obvious that spring-loaded actuators would be a very poor choice in a door lock system.

ichbineinekrous · #9 05-28-2008, 01:21 PM

The master switch in the drivers side door will release vacuum by design, the amount determines how many times you will be able to lock and unlock before recharging the system. I have gotten the system working in my 2 cars on 3 seperate occasions by doing nothing more than testing the system for leaks and detaching and re-attaching the three and 4-way connector along the driver and pass. side front floor. On one car I had to disconnect and plug the fuel door pod because it was leaking, and most recently had to disconnect the rear pass. side door to make the system functional. I've sealed the inlet of the vac. reservoir on both cars with silicone with good results.

Cr from Texas · #10 06-08-2008, 02:44 PM

Even with a small leak, you should be able to lock and unlock with the engine running unless your vacuum pump is weak. With the engine running, how much vacuum do you have at the large T off the brake booster line? Put a guage on that main line and if necessary, plug all of the other T connections. Mine will draw about 23" of vacuum.

mgcanuck · #11 06-08-2008, 07:40 PM

I pull 20" off the booster line..I get only about 12" at the 4-way connector to the check valve (door locks). This is ok, as it's still enough to shift the car. HOwever, when my check valve is plugged in, i only get about 5"! I pumped vacuum and it held at about 10"....i locked/unlocked the car and the vacuum dropped a bit then slowly came up. I've tested each vacuum line on the car floor, front/back, driver/passenger, trunk lock. They all hold vacuum.

I'm just wondering that since my 3/2 valve (going to the tranny) was leaking, maybe this extra demand is lowering the overall vacuum? That doesn't make sense, since that check valve is one-way, right?

After pumping up the reservoir line manually, the locks are now operating. However, i'm not sure the car will shift....that's next test..So maybe the resevoir needed to be completely recharged to keep the whole vacuum system at proper vacuum when hooked up??

mgcanuck · #12 06-08-2008, 08:04 PM

Hey, that totally seemed to have worked (pumping up vacuum at the 4-way connector). Once the reservoir was back up, the locks all work perfect, the car shifts properly and shuts down.

*Update

Reservoir went down overnight. I got enough vacuum to work the locks while running car for a bit, however not enough to shift properly. So, it would seem the 3/2 valve leak is still the issue. Getting a new one shortly.