FRONT AUTOMATIC AIR CONDITIONING SYSTEM : Air Flow Control

WARNING: This page is about a different car, the 2011 Nissan Quest. However, it is still accessible from the selected car via links, so may be relevant.

DESCRIPTION

A/C auto amp. changes duty ratio of front blower motor control signal to control air flow continuously. When air flow is increased, duty ratio of front blower motor control signal gradually increases to prevent a sudden increase in air flow.
In addition to manual control and automatic control, air flow control is compose of starting air flow control, low coolant temperature starting control, high in-vehicle temperature starting control, and fan speed control at door motor operation.

AUTOMATIC AIR FLOW CONTROL

A/C auto amp. decides target air flow depending on target front air mix door opening angle.
A/C auto amp. changes duty ratio of front blower motor control signal to control air flow continuously so that air flow matches to target air flow.
When air outlet is VENT or B/L, the minimum air flow is changed depending on sunload.

Fig 1: Automatic Air Flow Control Graph
Courtesy of NISSAN MOTOR CO., U.S.A.

STARTING AIR FLOW CONTROL

When front blower motor is activated, A/C auto amp. gradually increases duty ratio of blower motor control signal to prevent a sudden increase in discharge air flow. It takes approximately 8 seconds for air flow to reach HI from LOW.

NOTE: Do not perform the starting air flow control when the discharge outlet is set to DEF.

Fig 2: Starting Air Flow Control Graph

Courtesy of NISSAN MOTOR CO., U.S.A.

LOW COOLANT TEMPERATURE STARTING CONTROL

If the engine coolant temperature is 56°C (133°F) or less, to prevent a cold discharged air flow, A/C auto amp. suspends front blower motor activation for the maximum 150 seconds depending on target front air mix door opening angle. After this, front blower motor control signal is increased gradually, and front blower motor is activated.

Fig 3: Low Coolant Temperature Starting Control Graph

Courtesy of NISSAN MOTOR CO., U.S.A.

FAN SPEED CONTROL AT DOOR MOTOR OPERATION

When front mode door motor is activated while air flow is more than the specified value, A/C auto amp. reduces temporarily fan speed so that front mode door moves smoothly.

HIGH IN-VEHICLE TEMPERATURE STARTING CONTROL

When front evaporator fin temperature is high [intake air temperature sensor value is 35°C (95°F) or more], to prevent a hot discharged air flow, A/C auto amp. suspends front blower motor activation for approximately 3 seconds so that front evaporator is cooled by refrigerant.