I've got a '96 Bronco XL 302. Just today my A/C selector malfunctioned. THe compressor and fan speed selector seem to be working fine, but nothing will come out of the regular vents, just the defroster vents. I think there is a chip that regulates the flow of the system, I've heard they're pricey, I hope that isn't the problem. I'd love some advice.
-Shep

 

I had the same problem...its more than likely that you have a vaccuum leak somewhere in the control system. Its all buried behind the glovebox and dashboard but mine was just a single vaccuum line that had come loose. and instead of the previous owner figuring out where it used to be connected, he just tied a knot in it so it wouldn't hiss at him. Go figure.

 

It's not electronic other than the plain switches built into the control that select the fan speed & compressor clutch. The temp is cable-operated, but everything else is vacuum-operated. The supply line runs thru a rubber grommet in the top of the ventilation box under the R hood hinge, and another line comes out to the fresh/recirculate vacuum motor. You can probably see the supply line by looking up from the passenger footwell - it comes thru the plastic grate for recirculating air and goes up into the dash to the control. Follow it & the others & you'll probably find the leak, but don't forget to check the engine compartment side, too. The reservoir is glued to the side of the ventilation box that faces the R exhaust manifold.

 

what is a good way to check for a slight leak.
Mine will make the AC default to the defrost and floor vents, only sometimes and usually only when I am using the cruise control too.
I was told the reservoir runs out of vacuum and that's when it defaults? (not sure if I'm saying that right).

 

Thanks everybody for the advice. I fixed the problem. Turns out, it was a loose vacuum tube from the reservoir. I had seen the tube loose a day before but fugured it couldn't have been the tube for the reservoir. I couldn't believe that they just "push on" for my '96. Also, the A/C had worked that day despite the hose being loose. I guess it had finally lost pressure after a day or so? Thanks again, I think I look into securing the tubes a little tighter.

 

Get a vacuum pump (like the MityVac) and pull a vacuum on the supply line that goes thru the grommet by the R hood hinge. The system should hold vacuum until you switch the mode, and then only drop & hold again.