I was curious about the air vent flaps and starting taking things apart and followed various vacuum lines. I found out there is a relationship between the intake manifold, the PSE pump, and the air vent flaps. Below is a diagram with lots of picture of how these parts connect to each other. Afterwards, I will discuss my understanding of why they are connected to each other and how they work.
Locations and points of reference:
- The dashpot (#100) is located in the front passenger wheel well
- The distributor (#85) is located behind the outer side panel of the passenger foot well
- The switchover valve block is located under the glove box
- The PSE pump is located under the rear seat (next to the car’s 12V battery)
Below are the dashpot (#100) location pictures:
The green line on the dashpot (see picture above) connects to the distributor (#85). The grey line eventually goes to the back of the intake manifold, but it first goes to the engine compartment and connects to some sort of plug that just extends the vacuum line to behind the firewall. From there, it comes out from behind the firewall to the back of the intake manifold:
Above you can see the vacuum line connecting to an adapter that just extends the vacuum line to behind the firewall.
The above picture shows the vacuum line coming from behind the firewall (see plastic vacuum hose on far right of picture) connecting to a rubber hose then connecting directly to the back of the intake manifold where the vacuum assist port is located.
Getting back to the dashpot. The green line connects to the distributor (#85). The distributor is located behind the right plastic wall in the front passenger foot well:
In the above picture, the green line on the top of the distributor goes to the dashpot. The green line on the bottom of the distributor goes to the Switchover Valve Block (located under the glove box). The clear line on the bottom of the distributor goes to the PSE pump port labeled SRU (Manifold Vacuum Assist).
Above is a partial picture of the switchover valve block and the green vacuum hose that connects the switchover valve block to the distributor. Sorry for the bad picture, but it’s the only one I have. The green vacuum hose is not connected because I was documenting some work because I had broken connectors at the time. Anyway, you get the idea.
Above is a picture of the PSE pump which is located under the rear seat next to the car’s 12V battery. The clear line from the distributor (#85) connects to the SRU (Manifold Vacuum Assist) port on the PSE pump.
So, why are these components connected and how does all this work?
From what I can tell, the main reason these components are connected to eachother is to provide vacuum to control the air vent flaps.
Here’s a good explanation of how the air vent flap system works:
When you press the button on the climate control module to change the direction of air flow (for example, from the windshield to your feet), electrical signals are sent to the switchover valve which will open/close specific valves to control specific vent actuators. Opening/closing specific valves by itself does not open/close the vent actuators. The vent actuators are opened when vacuum is present on the line.
There is a vacuum line connected to the switchover valve. When the switchover valve opens a valve for a specific vacuum line, vacuum becomes present on that line which opens the actuator (and thus the air flap). When the switchover valve closes the valve, vacuum is removed from the line and the pressure on that line returns to atmospheric levels. This closes the vent actuator (and thus the air flap).
Of course, there are two sources of vacuum: The intake manifold and the PSE pump.
When the car engine is running, the intake manifold will provide the primary source of vacuum. When the car engine is not running, but the ignition key is in position #2, the PSE pump provides the primary source of vacuum.
There is also a dashpot located between the intake manifold and the switchover valve and PSE pump. I'm just guessing, but I think the primary reason for the dashpot is to zone the intake manifold line from the PSE pump vacuum line. If the car engine is not running, the PSE pump provides the vacuum. If the dashpot wasn't there, the PSE pump would run forever unsuccessfully trying to achieve a constant 17psi vacuum.
I hope this helps you. I rushed a bit to put this together to help answer someone else’s question.