Switch on dashboard does not change air direction to flow & vents
I have a 1999 F150, 4.2L, V-6. The switch on the dashboard that has the A/C, Floor, Defrost, Vent/Floor, etc. directions on it will turn on and off, however, it will not change the airflow directions when switched to the different locations/settings. Everything goes to the defrost. The other dashboard switches work fine for hot/cold and speed control. Can you help?
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Re: switch on dashboard does not change air direction to...
Defrost is the default mode so if the system fais, you alays have defrost. The mode doors are controlled by vacuum motors. I would suspect a vacuum leak in the engine compartment on the hose going from the engine through the firewall and into the heater controls. Some systems have a vacuum storage canister that can also leak. The canister stores vacuum when vacuum drops going up a hill.
Or, you have a bad heater control head that is not passing vacuum to the vacuum motors on the mode doors.
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Vacuum Control Motor-, Panel/Defrost Door
Panel/Defrost Door (Full Vacuum Position)
Defrost Air Flow
Side Window Demister Air Flow
Temperature Blend Door (Full Heat Position)
A/C Evaporator Core
Air Inlet Duct Door (Full Vacuum Position)
Outside Air Inlet
Vacuum Control Motor-, Air Inlet Duct Door
Recirculated Air Inlet
A/C Vacuum Reservoir Tank and Bracket
Vacuum from the Engine Intake Manifold
A/C-Heater Function Selector Switch
Vacuum to the 4x4 Hub Solenoids
Water Diverter Valve (Full Vacuum Position)
Floor/Panel Door (Full Vacuum Position)
Floor Air Flow
Vacuum Control Motor-, Floor/Panel Door
Panel Vent Air Flow
I the short answer is yes. The truck has a flow-thru vent feature as does most GM products. When the fan switch is off the outside air would flow into the truck. I thought you could still direct the air by way of the control panel, but by the wiring diagram it looks like everything is disabled when the fan switch is in the off position.
The "blender" would refer to the blend actuators that change the flow of air from floor to vent to defrost or combinations. Properly working blend doors will allow you to direct air to the dash vents, the floor, the defroster, the floor and defroster or the floor and dash vents. If it is not working the heater will still work but you will hae no control oer where the air flows.
From what I hear it is a vacuum line issue. Mine is doing the exact same thing. So, I am going to get a diagram and try checking the vacuum lines to see if any are loose or tore
I go under the dash and feel the air flowing out the floor and it is coming out of the defrost, also. I noticed under the drivers side today that air is flowing and there seems to be a gap in between a part under there. There was some material stuff I saw around the edge of it that sticky brown stuff and it sometimes before came out my vents all the time. Anyways, not sure if my air is just not sealed good to blow out the vents but it is something that happened not long ago and we've not done anything under our dash area.
You have a vacuum leak,defrost is the default postion,no vacuum to controls. Check the small black vacuum line that goes thru the firewall on the passenger side of the firewall and trace it back to see if you can locate a leak. It will go to a vacuum resivior then to the intake manifold.