Bought a 2003 lariat a while back, and could never get air flow from the defrosters or from the floor vents. Today I pulled the electronic control unit out of the dash just to take a look and found that the vac line plug (6 vac hoses) had been unplugged from the unit and a jumper vac hose put in from the vac supply line to the dash vent line. Without the jumper and with the vac stuff plugged back into the control unit, I just get defrost. In jumpering that vac hose to other positions, I can get floor air, defrost air, and floor/defrost. So far I havn't got dash/defrost. If I can get that I'll just leave it there I guess. "Won" an ebay auction last nite for the factory service manuals, maybe I can get some info there when I get it. When I select different modes, the lights on the control unit display correctly, so dunno what's going on. Any ideas? Tracka96

 

sounds to me like the seller tried to fix the vac problem backwoods style to get rid of the truck, afterall a truck with no a/c will not sell as great as one with a/c. if it were me i would take it to the local automotive a/c shop and have a diagnosis done, around here the a/c shop does free diagnosis. then take there opinion go home and go at it with the comfort of knowing exactly where the problem is.

 

Sounds like the vacuum source line is off or broken and leaking. Fix that.....OR,,,,
Connect that newly added vacuum source line to the vacuum source line near the vacuum plug/manifold that plugs in top the controlhead.