1995 f150 when using ac, an the vehicle reaches 40mph the air switches from ac vents to defrost, then i slow down to 35mph it switches back to vents constant problem

SOURCE: ac will not blow thru ac vents, only thru defrost vents.

if vent doors are operated by vacuum check for loose or broken vacuum hoses in the engine compartment , or check the fuse box for any ac/heat fuses if it is a electricaly controoled system

Jim Goldsmith

• 2005 Answers
• Posted on May 28, 2009

SOURCE: 1999 f350 ac blows from defrost vents instead of ac vents

check for a vacuum line that has fallen off the diaphram vacuum "switch can" near the vent shift lever at the heater box under the dash passenger side

SOURCE: AIR FLOW STUCK IN DEFORST VENT WILL NOT SWITCH TO FLOOR OR AC VEN

I found a broken vacuum hose on top of the intake which runs the controls

SOURCE: Ford F150 2003 When I press the max cool on the AC the air comes out of the windshield defrost vent iinstead of the cabin vents and is not as cold as it use to be. Summer in Texas Help !

You did not mention if the system you have is electronic(digital control) or manual(control knobs) but what your problem is, is a vacuum leak. Defrost and heat or the default postions for no vacuum. If it works ok until you press max air Then you will need to check the outside blend door vacuum motor. It will be the white vacuum line going from the control head.

SOURCE: My AC air registers only have air coming out of the defrost ducts

In every car, there are fins or flaps inside the dash that rotate that distributes the air flow from the blower to the desired opening, ie defrost, floor etc... This flap is controlled by a linkage which is connected to the selector switch. It may be the linkage is no longer connected, or the fins inside the dash are stuck. If the selector switch moves freely with little or no resistence its possible the linkage is no longer connected, otherwise the flaps need to be physically looked at.