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 and compares it with the current blower fan speed input 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 the obtained target temperature control door position, HVAC control module further calculates the target air flow control door position and controls the air flow control actuator so that the current air flow control door matches its 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)

- When the defrost switch is turned on or the "MODE" (air flow) switch is selected to "D/F" mode, HVAC control module fixes the position of the air intake control door to the FRESH position (FRE)

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 Description and Operation 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 input
- 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
- Ignition switch is turned on and defrost switch is turned on.
- Ignition switch is turned on and defrost "MODE" (air flow) switch is selected to "D/F" mode.

Condenser Cooling Fan Relay Control

ECM turns on the condenser cooling fan relay at the same time when ECM turns on the A/C compressor relay.