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Dynamic seat pump only runs when vacuum return line is unplugged
So I tore apart the interior and found an air line disconnected under passenger side rear floor. I reconnected it and pump runs but wouldn’t build pressure. I disconnected the vacuum return line from pump and noticed I couldn’t suck air from that line. When I leave it disconnected the pump runs and now builds pressure and seats work. I assume I shouldn’t leave the line disconnected but any ideas why it would be blocked? “Can’t suck or blow air in that line.
the picture below is the line that was disconnected under the floor inside car. Which I believe is the vacuum return line
Thanks that definitely helps. I’m thinking one of the vacuum switches must be set to pull vacuum and it can’t or shouldn’t be. I have unplugged the pump several times but never the fuse yet. I would think the vacuum return line has to be able to switch between vacuum when needed and being able to sucking fresh air somehow or the pump could never build pressure.
Thanks that definitely helps. I’m thinking one of the vacuum switches must be set to pull vacuum and it can’t or shouldn’t be. I have unplugged the pump several times but never the fuse yet. I would think the vacuum return line has to be able to switch between vacuum when needed and being able to sucking fresh air somehow or the pump could never build pressure.
or maybe I’m still missing something
If you're up to pulling your PSE pump, aka central locking vacuum pump, it may be worth a look inside. Untreated vacuum leaks can lead to overheating the motor inside and melting the plastic manifold within that contains the flow paths to your lines. There are also solenoids coils, a couple circuit boards and a lot of solder points inside that can fail as well. This quickly turns into how far do you want to go down the rabbit hole if you don't have SDS at your disposal to troubleshoot malfunctions.
If the pump itself is a problem, you can try to repair it in some cases, gamble on buying used ($200-ish) or buy new ($600-ish). From what I've read , I believe these need to be reprogrammed when replaced as well. This weekend I'll be replacing a pump motor with a new one ($60) and utilizing a used manifold from a bad ebay deal. The key to success is mitigating any vacuum leaks in your system to prevent excessive pump run time, prior to replacing the pump. I believe you can also adjust your pump run time and it's explained in the W220 wiki PSE section. If my repair doesn't go as planned, I'll suck it up and buy new and just chalk it up as a learning opportunity.
My trunk release actuator had a massive leak, the line to my dynamic seat pump had a split (which also had a burned out motor) and my central locking pump manifold was melted with a failing motor. So FWIW, you may have several issues that you haven't diagnosed yet.
I'll try to document what I do in case its of use to anyone. I'm sure this topic has probable already been beaten to death over the past 20 years.
This is a picture of the circuit board inside that pump. The airline closest to the electrical connector on the pump is attached to the integrated circuit with the "nozzle" on top. I believe it is an air pressure sensor. The air line farthest from the electrical connector is attached to the pump motor. When the pump is running it pumps air into all the air lines for the seats and headrests. If there are no air leaks in any of the lines, the lines pressurize and the air pressure sensor tells the pump motor to shut off. I don't believe there is a "vacuum line" anywhere in this seat/headrest module. This is only my opinion from tearing the pump apart and reading a few posts on rear headrests won't retract. I have no MB diagnostic tool or service manual.
I just bought a used S550 and my rear headrests won't retract. My pump was overheating and tripping a relay to shut off. I believe I have some cracked air lines and the air line to the pressure sensor IC never pressurized and told the pump motor to shut off. Again, this is my opinion from reading some posts and looking at the guts of the pump. This is my first post and I may be completely wrong.
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