four vacuum solenoids?

My truck has 4 vacuum solenoids on the fender by the wiper motor. All the vacuum diagrams I have found only show a maximum of 3. I noticed my A/C does not kick the idle up, I'm going to try switching the vacuum line for that to another solenoid I think it should go to. But then my question is where does this "fourth" solenoid go to and control?

Here is a picture:

Don't flip the vacuum lines. and yes you only have 3 solenoids. They are covered in the yellow rubber. I ditched the factory carb years ago and went Weber. So much simpler and only 1 or 2 vacuum hoses. Someone who still runs the factory carb should be able to help better.

I wish I could go weber right now, but I still have to pass one more emissions inspection before I get into the exempt category, plus I dont have the coin to drop on the weber right now.

By fourth, I meant the black non rubber covered one behind the set of 3 solenoids. What the heck is this thing, I thought that was the idle up solenoid which is why I was going to switch them. I guess the idle up solenoid is bad then since its not idling up. I'll try switching the solenoid out with another one and see what that does.

I think I still have one left-over solenoid in a parts box here.

Yes, can try to swap to isolate the issue. Make sure to mark the position on the solenoids so you don't forget which is which (note from experience).

The fourth solenoid as I recall activates the kick up diaphragm, which might itself be bad. You should be able to see the vacuum line that runs to it. The solenoid activates when the clutch for the AC compressor engages and the solenoid supplies manifold vacuum to the diaphragm for the kick up.


Hope this helps