Air Handling

WARNING: This page is about a different car, the 2017 Ford Escape. However, it is still accessible from the selected car via links, so may be relevant.

All airflow from the blower motor passes through the evaporator core. Based on the climate control system temperature settings, the temperature door actuator directs airflow through or around the heater core as needed. The air distribution door actuator controls the airflow to the defrost, floor or panel register vents. The air source is from outside air or recirculated passenger compartment air as determined by the air inlet mode door position.

The air inlet door actuator, air distribution door and temperature door actuators are stepper motors. There is no feedback circuit or potentiometer for these actuators. The pins labeled Door A, B, C and D are for the different phases (coils) of the motor. All the phases for a given motor are fed from a common power lead, the pin labeled Door Power and the HVAC control module controls each phase by turning a low side output on or off for the different phases. The motor turns or "steps" through a series of motions to position the actuator. The HVAC control module tracks the actuator positions by counting steps and periodically calibrates itself so it knows how many steps there are for the full range movement of the actuator. The HVAC control module sets Diagnostic Trouble Codes (DTCs) by monitoring the current flow through a given phase. If it sees too much current it identifies it as a short circuit. If it does not see any current it identifies it as an open circuit.

The blower motor is controlled using a blower motor resistor. The blower motor resistor uses 3 resistance elements that are wired in series on the ground side of the blower motor. The blower motor has 4 speeds:

for low speed, all 3 resistors are used
for medium-low speed, 2 resistors are used
for medium-high speed, 1 resistor is used
for high speed, the blower motor is provided a path directly to ground and the blower motor resistor is not used

The HVAC control module grounds 1 of the 4 circuits to control the blower motor speed.

OFF

When the system is OFF:

the air inlet door closes, preventing outside air and allowing only recirculated air.
the blower motor is off.

Max A/C

When MAX A/C mode is selected:

the air inlet door closes, preventing outside air and admits only recirculated air.
the recirculated air indicator is illuminated (recirculated air forced on).
the A/C button is illuminated.
the A/C compressor operates if the outside temperature is above approximately 2 °C (35.6 °F).

PANEL

When PANEL mode is selected:

the mode doors direct airflow to the instrument panel registers.
the recirculated air request button can be enabled.
blended air temperature is available. The airflow temperature can only be cooled below the outside air temperature when the A/C is commanded on.

PANEL-FLOOR

When PANEL-FLOOR mode is selected:

the mode doors direct airflow to the floor duct and the instrument panel registers. A small amount of airflow from the side window demisters and defrost duct is present.
the recirculated air request button can be enabled.
blended air temperature is available. The airflow temperature can only be cooled below the outside air temperature when the A/C is commanded on.

FLOOR

When FLOOR is selected:

the mode doors direct airflow to the floor duct. A small amount of airflow from the defroster duct and side window demisters is present.
the recirculated air request button can be enabled.
blended air temperature is available. The airflow temperature can only be cooled below the outside air temperature when the A/C is commanded on.

FLOOR-DEFROST

When FLOOR-DEFROST is selected:

the mode doors direct airflow to the floor duct, the defroster duct and the side window demisters.
the recirculated air request button can be enabled, but can automatically turn off.
blended air temperature is available. The airflow temperature can only be cooled below the outside air temperature when the A/C is commanded on.

DEFROST

When DEFROST is selected:

the mode doors direct airflow to the defroster duct and side window demisters. A small amount of airflow from the floor duct is present.
the recirculated air request button can be enabled, but can automatically turn off.
the A/C is automatically commanded on and remains on until the system is either turned off or the airflow mode has changed and the A/C button is pressed.
the A/C compressor operates as long as the outside temperature is above approximately 2 °C (35.6 °F).