Air Handling

WARNING: This page is about a different car, the 2018 Lincoln MKC. However, it is still accessible from the selected car via links, so may be relevant.

Based on the climate control system temperature settings, the temperature door actuators direct airflow through the evaporator and heater cores 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 door position.

The defrost, panel-floor, air inlet 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 FCIM 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 FCIM 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 FCIM 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 FCIM sends a PWM signal to the blower motor control module to control the blower motor speed. The blower motor 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 FCIM based on the temperature setting.
the mode doors are automatically controlled by the FCIM based on the temperature setting.
the temperature doors are automatically controlled by the FCIM based on the temperature setting.
A/C is automatically requested by the FCIM based on the temperature setting. The PCM does not operate the A/C compressor if the outside temperature is below approximately 0 °C (32 °F).
the blower speed is automatically controlled by the FCIM based on the temperature setting.

Off

When the system is OFF:

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