Driver Door Won't Unlock

[MBKid]

The driver's door lock on my 1995 C280 will lock via the vacuum system by the key at every lock point (driver, passenger, trunk) but will not unlock at any of the lock points. Now I can manually push over the key at the driver's door lock until it pushes up the lock, but the vacuum system will not push up the lock.

So after researching this great forum and other well known Mercedes forums I started inspecting some possible causes and here's what I found:

1. I have the much written about crack in the vacuum valve block located under the hood near the firewall/ECU. The crack is right at the silver ball bearing, but I can't tell if it's actually leaking or just a cosmetic crack.

2. I took off the driver's door panel and confirmed that air is being push and pulled by the vacuum pump via the yellow vacuum line to the door actuator. I have a vacuum tester but have never used it and so I can't confirm a leak anywhere in that line, but my thinking is if it's enough suction to lock the door and its pushing air out when trying to unlock, there may not be a leak.

3. I also have the much written about intermittent constantly humming vacuum pump I the trunk only when the AC is on. I'm assuming this is due to a cracked bellow that many have written about, but I have not taken apart the dash/glove box to check.

4. The driver's side passenger door lock has the same problem as the driver's door lock. It will lock but not unlock.

So what should my next move be? Replace the vacuum valve block (part #129 800 14 78)? Do the AC bellow replacement job as it may be related to the door lock? Do some kind of vacuum leak test (any help for a first timer on this would be much appreciated)? Buy a new driver's door lock actuator?

As the owner of a 1995 C280 and a 1996 C36 myself (both have this exact same lock problem BTW) I love these w202 forums and have used them many times over the years.

[Greeno]

I would start by making sure you have pressure and vacuum at the door lock actuator when it is trying to lock and unlock the door. If not it could be the PSE (vacuum) pump. You can also check the vacuum element in the door with a vacuum/pressure pump. They sell them at auto parts stores. Listen for leaks. Watch to see if the door locks and unlocks.

[MBKid]

I would start by making sure you have pressure and vacuum at the door lock actuator when it is trying to lock and unlock the door. If not it could be the PSE (vacuum) pump. You can also check the vacuum element in the door with a vacuum/pressure pump. They sell them at auto parts stores. Listen for leaks. Watch to see if the door locks and unlocks.


I appears to be the vacuum element (actuator) in the door as the PSE is providing enough vacuum and I checked with a vacuum tester and air compressor. Since its the driver's door, I'll need to remove the window to get the unit out and inspect. I'll post what I find when it's out.

[dzywicki]

1. I have the much written about crack in the vacuum valve block located under the hood near the firewall/ECU. The crack is right at the silver ball bearing, but I can't tell if it's actually leaking or just a cosmetic crack.


3. I also have the much written about intermittent constantly humming vacuum pump I the trunk only when the AC is on. I'm assuming this is due to a cracked bellow that many have written about, but I have not taken apart the dash/glove box to check.


I also have a 95 C280 and I recently went through your item #3 which included replacing the vacuum valve block under the hood. I had the crack too,but I don't think it was actually leaking. My problem for #3 was the bellows on the drivers side footwell. It's not too bad to diagnose which bellows it is. There is another vacuum control block under the glove box. If you remove the glove box and the panel underneath the passenger side dash, you can get the valve block out and check each line to see if/which one is leaking. 2 or 3 are accessible without removing the dash, the others require dash removal. I missed the drivers side bellows the first time I checked everything because I checked individual lines and the drivers side bellows is driven off of a T-line to the same bellows on the passenger side. I took the dash off twice, the second time only took about 45 minutes. I did a writeup on benzworld.org if you're interested. I also cataloged the part numbers for the bellows and proces from different places (BMA was the cheapest)

I have not had door lock problems, so can't help you there.