Theiskell

1: if my vacuum pump pulls 20” pounds of vacuum should the system hold that or is 15” OK
2: the vacuum switch that the wiper arm rests on that tells the system it is ok to close the wiper door. I cannot find what one of the hoses goes to. My diagram shows it going to nothing. Someone said it was a drain, but it has vacuum on it is this right

Alan 71

The 3rd hose is a vent hose and goes through the rubber grommet in the firewall with the other 2 hoses. It shows about 3 inches through the firewall. It doesn't need to connect to anything.
Regards,
Alan

Theiskell

Thanks Alan, With the wipers operating there is vacuum on that hose. It's a new switch is that normal?

7T1vette

Sounds like your lines are connected wrong on that switch. The "vent" tube should only exhaust vacuum when it needs to and should never have continuous vacuum on it. Also, 15" Hg is adequate vacuum; but whether it is 'good' or not depends on your engine. You need to measure idle vacuum with all the vacuum systems disconnected to see what your max. vacuum reading should be. Pull the vacuum supply off the intake manifold feed connector, connect the vacuum gauge to it, and plug off any other lines on that fitting. If the max. reading is not more than 16-17" Hg, then 15" with everything connected is pretty good...at least you don't have a bad leak. If your max. reading is around 20" Hg, you need to find the leaks in the system and should be getting around 18" with accessories connected.

Theiskell

The engine is out,the reading I am getting is with a vacuum pump. I will check the lines going to the switch again and re post

Theiskell

Ok, here is what I have: The switch is hooked up correct, but I still have vacuum on the vent tube when the wiper arm is off the switch. I went through and checked that the rest of the lines are in the correct position, and they are. I am pulling better vacuum now (19” hg) with the wipers down. I found a couple more leaks in the heater lines. Have I said I hate the vacuum system on these cars! Anyway the switch is new am I missing something, if I plug off the vent line it sucks in the boot around the switch.

7T1vette

Trying to diagnose and repair the C3 vacuum system with the engine not running is difficult, at best. You are doing the best that you can [under the circumstances] and your car has a much better chance of working properly, when you reassemble it, as a result. Good work.