hi, ive got an xg van and the vents are stuck on windscreen even though it has vacuum.
i had a look, theres a pretty strong vacuum coming from the black hose before it branches off to everything else under the dash, as soon as i plug it into the t piece (or whatever it is) the vacuum pretty much disappears and nothing works.

also, sometimes as i turn the vent switch i can hear a slight constant hissing coming from under the dash, its volume changes depending on the position of the switch, and i have no idea where its coming from.

Ive tried painting all the insides of the connections i can get to with a thin layer of gasket glue (carefully) to aid the sealing but still no luck.

i haven't checked the hoses under the bonnet yet, but i was spraying a can of that 'start ya bastard' stuff around the manifold looking for leaks the other night and the revs didn't change at all.
dunno if it makes a difference but the air con compressor doesn't kick in, pretty sure it only needs gassing.

ideas? its got me stumped. only thing i can think of is maybe the dash switches are rooted and leaking?

The black vac line comes off the intake from memory. There are also two other lines from the engine bay worth checking - green and orange. I think the green one has to do with activating the heater tap and the orange one has something to do with the thermostat (turns compressor off when engine temp rises). The other lines in the engine bay are mostly to do with the emissions system and probably aren't worth checking. If you have vac at the end of the black line where it plugs into the multi switch then lose vac when you plug it in then maybe the switch is gone. There is also a vacuum reservoir behind the dash (a black tank) which the black vac line also services. (supplies vac when the car is off). There are a fair few joiners behind the dash so you might have to take the dash out for a better look.

ive got most of the dash out atm, that main black vacuum line has a strong vacuum until i plug it it into the joiner and the rest of the hoses, is there any way to check the vent position switch and see if its failed/leaking??

im guessing the green and orange vac lines are okay, i can change between hot/cold and everything else, just i cant move the vents.
ill head out and double check everything now, haven't had a chance to work on it in daylight yet.

OK as far as I know there isn't a way to test the directional switch. I would just go to a wrecker and replace it. Before doing that though it may be worth checking the vacuum motor that controls the flap for the widscreen vents. This flap changes the air between the windscreen and main vents. The motor (ford call it a motor really its just a cylinder with a rod and one end and a plug at the other end for the vac hose) is right up under the ac/heater unit on top of the trans tunnel. I'm probably going a bit too far here as you say you have vac until you plug in the directional switch. Either the switch is dead or one of the motors on the end of the vac lines connected to the directional switch is losing vac. I would check the vac motor that controls that main flap for windsreen/main vents first (plug the black vac line that has vacuum into it and see if it closes.) If that motor works then it is likely the switch. A wrecker shouldn't charge you much for one of those. Sorry to ramble on...see how you go.

i recon that the switch is busted on closer inspection, i think i can hear it hissing if i wiggle the knob up and down without actually turning it. ill try replacing it, if it doesnt fix the stuck vents i think ill put up with them. i dont think i want the whole dash out id never get the prick back in lol

Quick fix is to wedge the main flap open at least that way you will have air out the vents not the windscreen.

cheers for that