Wiper door safety valve problem?

[Scott M.]

I have a question.
With the car running, wipers off and the wiper door closed...
If the passenger side wiper arm becomes "un-parked", is the vent hose on the wiper door safety valve supposed to have a constant vacuum leak to atmosphereric pressure?
I guess another scenario would be if you where driving along one rainy day and then the rain stops, you turn your wipers off, but for some reason they don't go down all the way...
1. of course the wiper door won't close
2. a vacuum is actively being applied to that safety valve, which seems vents to atmosphere
Couldn't you eventually lose all the vacuum in the tank, causing the headlights to pop up and a less than desireable performance from your engine?
Thoughts anyone?

[Paul D.]

Re: Wiper door safety valve problem?

Only if the hoses are hooked up wrong. If the wiper system is operating correctly now, try swapping the vacuum source hose and the one that goes to the vacuum relay valve. Leave the vent hose alone. I think that switch allows vacuum to the wiper door relay when open, but seals the source port when closed. The vent hose releases the vacuum to the relay valve. Originally, the hoses were color coded there and the valve had color dots on it to indicate which hose went where. I don't claim to be an expert, but did spend a lot of time working on the wipers/headlamps on my 71 years ago. Chip.

[Jack H.]

Re: Wiper door safety valve problem?

With the engine running, you'll be making/replacing vacuum lost to the venting process faster than you're losing it. Plus, designers were careful to route that vacuum vent line from the switch in the cowl back through the grommet in the firewall so the stub end wasn't in an open to the rain environment allowing it to 'suck' airborne moisture back into & through the system.

Think for a minute... When you tell the wipers to actuate (or ask the headlights to raise), vac is vented on the control lines in the cockpit at the actuating switches. Plus, in the case of the wipers, vac is vented in the cowl (via the vent hose to the engine compartment) by the wiper park switch for as long as the wipers are in operation and doesn't stop venting until the wipers re-park.

By your line of thought, the Corvette would run out of vacuum if you drove for any extended period of time in the rain with the wipers in operation. We know that doesn't happen, eh?