74 F100 has factory AC, it has a throttle advance solenoid so that when the air is on it speeds up the engine off idle, where can i get a replacement solenoid?

 

That solenoid isn't for AC. Called an "idle stop" solenoid, its job is to maintain the engine idle speed when the ignition is on. When the ignition is shut off, the solenoid retracts, which allows the throttle plates to shut. This is to keep the engine from dieseling. Idle stop solenoids were added as emissions equipment became more common, which typically lead to higher combustion chamber temperatures. You'll notice the solenoid is mounted on a bracket that can be moved closer or farther away from the carburetor body via a long set screw; this is how curb idle speed is adjusted on motors equipped with the solenoid.

To answer your question, though, these are hard to find. I'd see if you can get lucky with Napa or Rock Auto.

 

I believe the A/C style solenoid started in 77, or possibly 80. It was a 2 step solenoid that acted as an anti-dieseling solenoid and a second step for higher A/C RPM.

Motorcraft CS4 is what I have written down. I googled that and got a ton of frivolous info... hmmm...

Josh

 

This solenoid is tied to a factory wiring harness on the engine and only advanced the throttle or worked when the air conditioning was turned on. I did see it work before it finally quit and this was the only time it engaged.

 

The solenoid SHOULD have been active with KEY ON. So a PO wired it into the A/C compressor harness and must have done a good job if it looks factory.

As FMC400 pointed out, the solenoid is considered an ANTI-DIESELING solenoid.

Josh