HVAC Control Description

HVAC Control Description

Temperature Control
HVAC control module calculates the target temperature control door position based on signals from the temperature selector, inside air temperature sensor, outside air temperature sensor and sunload sensor and controls the temperature control actuator so that the current position of the temperature control door matches its target position.

Fan Speed Control
HVAC control module calculates the target blower fan speed based on signals from the temperature selector, inside air temperature sensor, outside air temperature sensor, ECT sensor and sunload sensor, compares it with the current blower fan speed inputted from the blower motor controller to control the current blower fan speed to the target level.

Air Flow Outlet Control
HVAC control module calculates the target temperature control door position based on signals from the temperature selector, inside air temperature sensor, outside air temperature sensor, ECT sensor and sunload sensor. Using thus obtained target temperature control door position, it further calculates the target air flow control door position and controls the air flow control actuator so that the current air flow control door position becomes the target position.

Air Intake Position Control
HVAC control module determines the position of the air intake control door based on signals from the temperature selector, inside air temperature sensor, outside air temperature sensor and sunload sensor and selects any of the following positions by controlling the position of the air intake control door.
^ FRESH position (FRE)
^ RECIRCULATION position (REC)
^ MIX position (MIX)

A/C Compressor Relay Control
HVAC control module outputs A/C switch ON signal to ECM via BCM when the vehicle state satisfy conditions described below.
^ A/C switch is ON
^ Evaporator temperature is higher than specified value
^ Evaporator temperature sensor malfunction is not detected

Communication of ECM and BCM is established by CAN (Controller Area Network). (For more detail of CAN communication, refer to CAN Communication System Description). ECM turns ON the A/C compressor relay when the vehicle state satisfy conditions described below.
^ A/C switch ON signal is inputted
^ A/C refrigerant pressure is within specified range
^ Engine speed is within specified range
^ Engine coolant temperature is lower than specified value
^ Throttle opening is lower than specified value
^ Vehicle is not in either state of starting or quick acceleration
^ ECT sensor malfunction is not detected
^ A/C refrigerant pressure sensor malfunction is not detected

Condenser Cooling Fan Relay Control
ECM turn ON the condenser cooling fan relay at the same time when ECM turn ON the A/C compressor relay.