neat

I think I understand the wiper door vacuum system, but I'd like someone to confirm that I follow everything properly, so please correct me on the following statements where I've messed up. I also have a question or two at the end:

When relaxed, the relay valve allows vacuum to pass from the center (yellow) port to the lower (green) port. This pulls on the 'open' side of the actuator. This creates a situation in which if the control circuit fails, it is likely the door will open.

When vacuum is applied to the small port of the relay via the white striped hose, the relay allows vacuum to pass from the center (yellow) port to the top (red) port. This pulls on the 'closed' side of the actuator.

The safety valve center port receives vacuum from the over ride valve. If the wiper arm is up, the safety valve connects the center port to atmosphere. If the wiper arm is down, depressing the valve plunger, vacuum is routed to the bottom port and onto to the relay valve. If this valve were laying on the bench, it should not pass air between the center and bottom ports while relaxed.

The over ride valve gets vacuum from the wiper control solenoid. It is open or closed manually.

The wiper control solenoid is normally open, allowing vacuum to pass through it to the rest of the system and ultimately to the small port on the relay. When you turn the wipers on, the solenoid closes, vacuum is cut off from the system - and ultimately from the small port on the relay. This allows the relay to return to a relaxed position, pass vacuum to the green port, and pull on the 'open' side of the actuator.

I am wondering why the wiper door is not always open when the car is off? When you shut the car off, the vacuum reservoir still feeds the center port on the relay indefinitely (until the reservoir leaks down). The wiper solenoid and safety switch are open to atmosphere once the engine stops running, which means there is no pull on the small port on the relay, allowing the relay to return to the relaxed position. In it's relaxed position, why doesn't the vacuum from the reservoir pull open the wiper door?

If I follow everything right, there needs to be constant vacuum on the small port on top of the relay to keep the wiper door from opening, right?

Thanks!

zwede

From what I remember, this doo-hickey is a check valve:



So the vacuum tank is just a reservoir and supplies vacuum to both the power as well as the control circuit after the engine is off. Therefore the lights & wiper door stays down.

Dave J

When the wiper arm is up, and the plunger is extended on the safety valve, there should be no vacuum escaping to atmosphere on the center port. If you put a vacuum gauge on the center port, it should hold vacuum, and not leak down.

Think about why the wiper arm would be up. Pulling the override valve or activating the wiper control solenoid does expose the circuit to atmosphere. The loss of vacuum from the safety valve would de-energize the spring plunger in the relay, passing vacuum to the lower port, in turn raising the wiper door. This would then activate the wiper switch, turning on the wipers and then raising the safety valve plunger if the wiper solenoid was used.

While the wipers are in use, everything works fine. The issue is when the wiper solenoid is de-energized and passes vacuum to the safety valve. There is now a vacuum leak at the safety valve using your analogy.

This is true. Let me also add that the safety valve should hold vacuum and not leak down at this point.

This is also true. If it did, you would have mass chaos with your wiper door and the wipers. The center port should hold vacuum at this point. It really doesn't matter what the bottom port does here.

Alan 71

Hi neat,
To your last question.... not necessarily.
There are 2 important keys to the operation of the head-light doors and wiper door.
First, if all seals in the actuators and relays are good the doors stay in the position they are as the vacuum leaks down.
Second, the system depends on the fact that the 'control' hoses are small (white) and the 'servo' hoses are large (red, close; green, open; yellow, supply). Because of this difference when you start the car after the vacuum has leaked down the 'control' function is re-established BEFORE the 'servo' function is, (because of the hose's smaller capacity), and the doors stay where they are.
IF the system has leaking relays the 'servo' side of the system may power up first, then the doors open briefly until the the 'control' side of the system powers up and returns the doors to their 'as set' position. The problem is often known as 'winking headlight door and dancing wiper door syndrome'.
Big Fun.
Regards,
Alan

neat

The way I understand it is:

There should be a vacuum leak at the safety valve at this point. Only once the wipers have returned to the park position and pressed the safety valve plunger should vacuum be routed from the vent port to the bottom port - and in turn to the relay which will ultimately result in closing the wiper door. I think the idea was to prevent the door from closing on the wipers if they were up for some reason.

If I read you correctly, I am wrong thinking the safety valve operates in this manner?