Just got my X and trying to learn all that I can. 2002 7.3

No matter what setting I put the AC on, air will only blow up by the windshield. It will not come out of the vents.

Any advice on what I should check? I am a beginner mechanic and need all the help I can get.

 

Vacuum lines or pump issue, maybe fuse to pump, fuse 27...
here is a link with more troubleshooting. It applies to excursions https://www.ford-trucks.com/forums/1...t-vents-2.html

 

4x4 vacuum switch is a common problem which causes the AC to default to the defroster. It’s located on the passenger fender right behind the battery, they crack and cause a leak. Part is about 50 bucks and takes all of 5 minutes to replace. Take a look at that ,fixed mine after two years of frustration. Good luck.

 

To clarify, as this may not be obvious to someone new to the trucks (I had to learn it)...

Ford used vacuum to control the HVAC flapper system that routes air to various places. It's designed such that if you do not have vacuum to the under-dash flapper controllers or valves, the flapper system defaults to the defrost position. This is the "safe" position as defrost is the most-safe need.

So by your HVAC not able to select anything but defrost, that implies you're not getting any vacuum to the truck, or the controls are not working correctly, or one of more of the control diaphrams are not working.

Further, given yours is a diesel, note that diesels do not have intake manifold vacuum like a gasser (there's no throttle plate) so your vacuum is provided by a vacuum pump, located on the right inner fender under the hood. It's a little pump mounted near the hood, and has vac lines going into a vacuum reservoir, a black rectangular box right next to it. You'll see a black vac line heading back toward the interior, and that's the supply line to the under dash stuff.

FINALLY, Ford also uses that same vacuum system to control the front hubs on the SOTF 4x4 system; that vacuum pulls in a plate that locks in the front hubs.

First test: is the vacuum pump working? Do you hear it running when you turn the key on (it may be faint, stand on the passenger side with the hood up while someone turns the key on, no start)? You typically should hear the pump run a few seconds or so.

If you have a leak in the vacuum system, the pump will run constantly. If that is happening, find and repair the leak; as noted above, it's commonly the SOTF hubs. If that's the case, you can temporarily remove the lines going forward to the hubs, put a vac cap on the lines going back to the vac system, and manually engage the hubs until you get around to fixing the vac lines.

If the pump is not coming on, find the vac fitting that goes into the black reservoir and carefully remove it; you should hear hissing (that's air leaking into the reservoir) and the pump should start immediately. If neither of those happen then you have a pump problem.

Top tip: on my 2001 Ex, the pump is on the same circuit as my reverse lights and turn signals. If you do not have turn signals or reverse lights then (as noted above) it's possibly a blown fuse (on mine, under the dash, on the right fourth fuse up...15A?)

Start there, then come back with what you've learned.

GA