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 actuators direct airflow through or around the heater core as needed. The air distribution door actuators control 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 defrost vent/register, air inlet, footwell vent 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 HVAC control module sends a PWM signal to the blower motor speed control to control the blower speed. The blower speed control provides variable ground feed for the blower motor. A delay function provides a gradual increase or decrease in blower motor speed under all conditions.

AUTO

When AUTO is selected:

the HVAC system operates in a manner to achieve and maintain the temperature set by the operator.
the air inlet door is automatically controlled by the HVAC control module based on the temperature setting.
the mode door is automatically controlled by the HVAC control module based on the temperature setting.
the temperature blend door is automatically controlled by the HVAC control module based on the temperature setting.
the A/C compressor is automatically controlled by the HVAC control module, based on the temperature setting. The A/C compressor does not operate if the outside temperature is below approximately 2 °C (35.6 °F).
the blower motor speed is automatically controlled by the HVAC control module based on the temperature setting, but can be manually overridden.

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 footwell vent doors and defrost vent/register doors operate in combination to direct airflow to the instrument panel registers.
the temperature blend doors move to the full cool position. Air temperature can be manually overridden.
the A/C button is illuminated.
the A/C compressor operates if the outside temperature is above approximately 2 °C (35.6 °F).
the blower motor is commanded to the highest speed. The blower motor speed is adjustable.

PANEL

When PANEL mode is selected:

the recirculated air request button is enabled. If the recirculated air request button is selected (indicator on), the air inlet door closes, preventing outside air from entering the passenger compartment. If the recirculated air request button is not selected (indicator off), the air inlet door opens, allowing only outside air into the passenger compartment.
the footwell vent doors and defrost vent/register doors operate in combination to direct airflow to the instrument panel registers.
blended air temperature is available. The airflow temperature can only be cooled below the outside air temperature when the A/C is commanded on.
the blower motor is on and the speed is adjustable.

PANEL-FLOOR

When PANEL-FLOOR mode is selected:

the recirculated air request button is enabled. If the recirculated air request button is selected (indicator on), the air inlet door closes, preventing outside air from entering the passenger compartment. If the recirculated air request button is not selected (indicator off), the air inlet door opens, allowing only outside air into the passenger compartment.
the footwell vent doors and defrost vent/register doors operate in combination to 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.
blended air temperature is available. The airflow temperature can only be cooled below the outside air temperature when the A/C is commanded on.
the blower motor is on and the speed is adjustable.

FLOOR

When FLOOR mode is selected:

the recirculated air request button is enabled. If the recirculated air request button is selected (indicator on), the air inlet door closes, preventing outside air from entering the passenger compartment. If the recirculated air request button is not selected (indicator off), the air inlet door opens, allowing only outside air into the passenger compartment.
the footwell vent doors and defrost vent/register doors operate in combination to direct airflow to the floor duct. A small amount of airflow from the defroster duct and side window demisters is present.
blended air temperature is available. The airflow temperature can only be cooled below the outside air temperature when the A/C is commanded on.
the blower motor is on and the speed is adjustable.

FLOOR-DEFROST

When FLOOR-DEFROST mode is selected:

the recirculated air request button is enabled. If the recirculated air request button is selected (indicator ON), the air inlet door closes, preventing outside air from entering the passenger compartment. If the recirculated air request button is not selected (indicator OFF), the air inlet door opens, allowing only outside air into the passenger compartment.
the mode doors direct airflow to the floor duct, the defroster duct and the side window demisters.
blended air temperature is available. The airflow temperature can only be cooled below the outside air temperature when the A/C is commanded on.
the blower motor is on and the speed is adjustable.

DEFROST

When DEFROST is selected:

the recirculated air request button is disabled. The air inlet door opens, allowing only outside air into the passenger compartment.
the footwell vent doors and defrost vent/register doors operate in combination to direct airflow to the defroster duct and side window demisters. A small amount of airflow from the floor duct is present.
the A/C is turned on in DEFROST. The A/C compressor operates as long as the outside temperature is above approximately 2 °C (35.6 °F).
blended air temperature is available.
the blower motor is on and the speed is adjustable.

MAX DEFROST

When MAX DEFROST is selected:

the recirculated air request button is disabled. The air inlet door opens, allowing only outside air into the passenger compartment.
the air distribution doors operate simultaneously to direct airflow to the defroster duct and side window demisters. A small amount of airflow from the floor duct is present.
the A/C is turned on in MAX DEFROST. The A/C compressor operates as long as the outside temperature is above approximately 2 °C (35.6 °F).
the temperature is set to the highest setting and is not adjustable.
the fan is set to the highest speed and is adjustable.
MAX DEFROST can be exited by pressing the AUTO button.
REAR DEFROST automatically turns on.