Vacuum pump runs constantly

[spastik monkey]

I've recently noticed my vacuum pump runs constantly with the key on. The AC defaults to defront but will switch to whatever setting after a few seconds once the engine starts running. Any idea what would cause this?

[F250SixOH]

Solenoid or a leak in your hubs most likely

[spastik monkey]

Is there an easy check for this? I have a set of SS ESOF lines coming.

[F250SixOH]

First take off the line that goes to the solenoid and hook your vacuum gauge to it. It should pump up quickly and hold constant. This confirms no leaks in the pump or tank. Then reconnect and hook up gauge after the solenoid. See what happens then. If that still is fine then connect the vacuum gauge to the line that goes to the hubs and pump it to 10 or 15psi. If there are no leaks it should hold constant. If there are leaks, then you need to troubleshoot farther. Usually it is the solenoid that goes bad. (In my case it was) This should be enough to get you started

[spastik monkey]

The pump builds pressure, and it build pressure in the tank when the red line to the solenoid was disconnected. Is there a definitive check for this solenoid?

[F250SixOH]

For the solenoid you can simply put your finger over the line going to the hub. If the pump builds vacuum and stops then it's fine. If the pump keeps going then the solenoid is bad. That's probably the most simple test that I can think of for it right now

[spastik monkey]

I know that when I click it into 4wd the vents go to defrost. Where does one get one of these aforementioned solenoids?

[F250SixOH]

Originally Posted by spastik monkey

I know that when I click it into 4wd the vents go to defrost. Where does one get one of these aforementioned solenoids?

The stealership and you will be happy to know that the solenoid has been superseded to an $80 part. Might be cheaper on Tousley.

Part number for my 05 is 7C3Z-9H465-A

If you just want to live with manual hubs and keep good working air conditioning you can just plug the line before the solenoid

[spastik monkey]

I switched the solenoid. Still does it. However if I disconeect tje line going to the solenoid and check vacuum there it builds pressure fine. Theres no audible leak

[F250SixOH]

That's really weird. Check the electrical connection as well.