Air only comes out of dash (in your face)??? - 1988 Ford F 150

check for a fuse for that control switch if it controls power
it may be a switch that moves valves to allow air to the vent actuators check for air line connections
talk with a kenworth service centre.

usually a faulty blend door under the dash

The ducts have dampers that work off of a vacuum and control the flow of air to the different air vents at the top, bottom and face of the dash. Sometimes the vacuum lines come loose or break. You'll need to look under the dash to see if any of these conditions exist.

I think your problem is the head unit that selects where the air comes out ie. Face, floor, defrost, or hi-level face and floor. If that's not working then it will not let you switch location that you want the air to come out.

Does your vehicle have manual or automatic climate control ? You system is stuck in floor an defrost mode ?

Item Part Number Description 1 18A318 Vacuum control motor-floor/defrost door 2 - Defrost air flow 3 18A478 Floor/defrost door 4 18476 Heater core 5 19860 Evaporator core 6 19805 Blower motor 7 - Outside air inlet 8 19A813 Air inlet door 9 18A318 Vacuum control motor-air inlet door 10 - Recirculated air inlet 11 18B545 Temperature blend door 12 18A559 Panel door 13 - Panel air flow 14 18A318 Vacuum control motor-panel door 15 - Floor air flow 16 - Vacuum from the engine intake manifold 17 19A563 A/C vacuum check valve 18 19A566 Vacuum reservoir tank and bracket 19 19980 EATC control
Pull the control panel an check for vacuum

Item Part Number Description 1 White Air inlet door 2 Yellow Floor/defrost door 3 Red Floor door 4 Blue Panel door 5 Black Source vacuum 6 - Not used


VACUUM APPLICATIONS CHART-ELECTRONIC AUTOMATIC TEMPERATURE CONTROL Switch Port Vacuum Harness Hose Color Func- tion Manual Override Selector Buttons OFF MAX A/C NORM A/C VENT FLOOR FLOOR/ DEF DEF 1 White Air inlet 2 Yellow Floor/ panel (partial) 3 Red Full floor 4 Blue Panel 5 Black
Source

2 possible problems, #1 is the control switch on the dash has malfuntioned(less likely) , #2 is the motor under the dash that changes the blower position is not working properly.

Please rate my answer ............Thanks

TSB 03-01-38-005d, is to replace the foam in the mode door valve.
foam comes loose and prevent the mode door from moving.
The whole dash must be removed to installed the new foam.
Part number gm
89018656

check the hoses connected to the vacuum advance ball, it has probably begun to decompose...

I have had ductwork under the dash come undone and cause this-depending on your vehicle, the ducting to your face/feet vents may snap into place. Also the switch that directs the air may not be working, or just not directing to those vents for some reason. Take a quick look underneath and see if you can see anything obvious. Sometimes a vent has just come undone from the rest of the system and needs to be popped back on.