Vacuum control motors are used to position these airflow control doors.
SECTION 412-01: Air Distribution and Filtering
2000 Expedition/Navigator Workshop Manual
DESCRIPTION AND OPERATION
Procedure revision date: 06/17/1999
There are two sources of air available to the air distribution system:
- outside air
- recirculated air
Recirculated air is only used during MAX A/C, AUTOMATIC (if equipped with EATC) and OFF modes.
Air distribution within the vehicle is determined by the function selector switch position, if equipped with manual A/C, or is controlled by the electronic automatic temperature control system in the AUTOMATIC mode but can be overridden by the driver if desired. Airflow control doors are used to direct airflow within the heater air plenum chamber. Vacuum control motors are used to position these airflow control doors.
The air distribution system is designed to provide airflow from the defrost nozzle when no vacuum is applied to any of the vacuum control motors. This is done to prevent a situation where defrost cannot be obtained due to a system vacuum leak.
Air enters the passenger compartment from the:
- instrument panel A/C registers.
- heater outlet floor duct.
- windshield defroster hose nozzle.
- side window demisters.
- rear seat airflow duct (if equipped).
Passenger compartment air is exhausted from the vehicle through open windows or cab air vents.
Vacuum control motor - panel/defrost door
Panel/defrost door (full vacuum position)
Side window demister airflow
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
Vacuum to emission control
Vacuum from the engine intake manifold
A/C vacuum check valve
A/C vacuum reservoir tank and bracket
A/C-heater function selector switch
Floor/panel door (full vacuum position)
Vacuum control motor - floor/panel door
Panel vent airflow
Check vacuum control to the panel defrost motor ( vac,diaphragm )