W124 vacuum vent line

[Zulfiqar]

In a W124.131 there is a black vacuum line that goes into the cabin, it supposedly vents the vacuum valve on the pump which controls the transmission modulator. in my car it is also shared by the resonance flaps..

anyway - does this black line actually have some sort of thing to connect to in the cabin, I pulled it out because the resonance flaps would get hung up and also the modulator would act funny sometimes.

When I pulled it out, it felt that there was nothing holding it - good news is that the system does not hang now.

[jay_bob]

Whenever you have a vacuum actuator you apply vacuum to make it do whatever it does (for example, change the shift behavior of the transmission, or activate the EGR valve).

In order to relax the actuator you have to relieve the vacuum by admitting air into the system. In the under hood environment you don't want to be pulling ambient air into the system, it is wet and dirty air.

So the air inlet draws from the cleanest, driest source of air available, which is the cabin. The "vent" hose is sucking air from the cabin to the actuator to break the vacuum and release the actuator when the system decides it is time to do that.

The end of the hose just hangs out under the dashboard and that is all it is supposed to do.

[Zulfiqar]

Originally Posted by jay_bob

Whenever you have a vacuum actuator you apply vacuum to make it do whatever it does (for example, change the shift behavior of the transmission, or activate the EGR valve).

In order to relax the actuator you have to relieve the vacuum by admitting air into the system. In the under hood environment you don't want to be pulling ambient air into the system, it is wet and dirty air.

So the air inlet draws from the cleanest, driest source of air available, which is the cabin. The "vent" hose is sucking air from the cabin to the actuator to break the vacuum and release the actuator when the system decides it is time to do that.

The end of the hose just hangs out under the dashboard and that is all it is supposed to do.

Thanks..

[Wusha]

Thank you, this solved my mystery black hose.