Vacuum pump was replaced about 3 months ago because the old one was dead. No problems with the new one after installation but now it runs non stop. If I let the truck idle for a few minutes before I cut on the AC it blows out of the vents, then after about 30 seconds it switches to half vent and half defrost.

I searched the old threads but do not see what I am looking for.

This is what I can tell you. If I unplug the hose that goes into the AC box under the hood the pump shuts off. That tells me that there is a vacuum leak under the dash. I opened up the glove box and unplugged the 3 hose (black, grey, white) connection and plugged that and the pump stops so I know the leak is after that connection.

What I am trying to figure out is, does this tell me the control panel for the AC has a leak inside or is there something else I need to be looking for?

 

i thought my leak was in the same place when i plugged them off it cut out i never did find a leak in the heater vacuum lines it was in inside the pass side wheel well where the vacuum line splits into a T the line going in was cracked good luck vacuum leaks are frustating as hell to find

 

Check out the link below.

https://www.ford-trucks.com/forums/8...ml#post7788534

I bet your solenoid valve is bad?

Read through the thread above and scroll down to one of my posts where I show a photo of the various vacuum line things to look at.

Hope this thread helps you fix your problem or places to look?

Good luck.

 

Thought I would post an update to let you know what I found. Unfortnately I did not find anything but somehow I fixed the problem.

I took the front dash apart so I could acess everything related to the vacuum lines. Then I removed all the lines and put them right back on making sure they were all connected securely. I turned the key on and waited for the vacuum pump to turn off and within 30 or 40 seconds it shut off. I cycled everything thru on the AC control panel and the vacuum pump never came back on. I also let the truck run for about 10 minutes and never did notice that the pump came on and I checked it frequently with my hand to see if was running. Sorry I was not able to post a solution but maybe someone else having the same problem might have a place to start.