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FULL-AUTO AIR CONDITIONER SYSTEM [FULL-AUTO AIR CONDITIONER]

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2016 – MX-5 – HVAC

FULL-AUTO AIR CONDITIONER SYSTEM [FULL-AUTO AIR CONDITIONER]

Outline

  • The climate control unit performs the following controls based on the input signals from the each dial/switch and each sensor.

Control item

Control description

Airflow temperature control

  • Airflow temperature automatic control

    • MAX HOT and MAX COLD correction

    • Engine coolant temperature correction

Airflow volume control

  • Airflow volume manual control

  • Airflow volume automatic control

    • Engine coolant temperature correction (warm-up correction)

    • Mild start correction

    • MAX HOT and MAX COLD correction

    • Start-up window fogging prevention correction

    • Defroster correction

Airflow mode control

  • Airflow mode manual control

  • Airflow mode automatic control

    • Engine coolant temperature correction (warm-up correction)

Air intake control

  • Air intake manual control

    • RECIRCULATE mode control under severe heat

    • FRESH control in defroster mode

A/C compressor control

  • A/C compressor manual control

  • A/C compressor automatic control

    • Defroster correction

  • A/C cut-off control

Supplementary function

Sensor signal delay function

Fail-safe

On-board diagnostic feature (See ON-BOARD DIAGNOSTIC.)

Functions

Airflow temperature control
  • The airflow temperature control operates the air mix actuator in conjunction with the set temperature and vehicle conditions, and switches the air mix damper position.

  • The climate control unit calculates the opening angle characteristic of the air mix actuator based on the set temperature, solar radiation amount, and the airflow mode.

  • The air mix actuator opening angle characteristic decreases as the sunlight intensity increases.

  • The airflow temperature is automatically controlled continuously.

  • The following are the airflow temperature control corrections.

    • MAX HOT and MAX COLD correction

    • Engine coolant temperature correction

    MAX HOT and MAX COLD correction

  • When the temperature is set to 29 °C or 84 °F, the air mix actuator opening angle is fixed at fully open, and when set to 15 °C or 60 °F, it is fixed at fully closed.

    Engine coolant temperature correction

  • The engine coolant temperature correction sets the opening angle of the air mix actuator more to the HOT side than during normal control when the engine coolant temperature is lower than the specified value to prevent discomfort caused by cold air blown from the vents after the engine is started in winter.

  • The engine coolant temperature correction is not performed when the ambient temperature is 15° C {59 ° F} or more.

Airflow volume control
  • The airflow volume control changes the operation of the blower motor according to the operations of the airflow volume control dial or temperature control dial and the vehicle environment to change the airflow volume.

  • The airflow volume control has automatic and manual controls.

  • The airflow volume automatic control performs the following corrections:

    • Engine coolant temperature correction (warm-up correction)

    • Mild start correction

    • MAX HOT and MAX COLD correction

    • Start-up window fogging prevention correction

    • Defroster correction

    Airflow volume automatic control

  • The climate control unit calculates the blower motor applied voltage characteristic based on the set temperature and ambient temperature.

  • The climate control unit compares the blower motor applied voltage characteristic with the target temperature (calculated control value T3) and then determines the blower motor applied voltage (AUTO voltage).

  • The calculated control value T3 is the target cabin temperature as set by the climate control unit based on the difference between the set temperatures and temperatures input from the sensors.

  • The calculated control value T3 is constantly calculated according to the changes in the set temperature and the signals input from the sensors.

    Airflow volume manual control

  • The climate control unit changes the blower motor applied voltage in seven steps according to the operation of the airflow volume control dial.

Airflow volume setting

Blower motor applied voltage (reference)

1st

3.8 V

2nd

5.6 V

3rd

7.4 V

4th

9.1 V

5th

10.5 V

6th

11.9 V

7th

14.0 V

    Engine coolant temperature correction (warm-up correction)

  • The engine coolant temperature correction (warm-up correction) controls the blower motor applied voltage in conjunction with the increase in the engine coolant temperature to prevent a high volume of cold air from flowing out of the air vents after starting the engine in the winter.

  • The engine coolant temperature correction (warm-up correction) is not performed during defroster correction, or when the cabin temperature is 20 °C {68 °F} or more and the airflow mode is in VENT mode.

    Mild start correction

  • The mild start correction prevents a high volume of air from blowing out of the air vents when the blower motor is started.

    MAX HOT and MAX COLD correction

  • The MAX HOT and MAX COLD correction fixes the blower motor applied voltage as indicated in the table when the temperature is set to MAX HOT or MAX COLD.

  • The MAX HOT correction is not performed during engine coolant temperature correction (warm-up correction).

Correction

Set temperature (°C/°F)

Blower motor applied voltage (V)

MAX HOT correction

29/84

12.1: AUTO-HI

MAX COLD correction

15/60

B+: MAX-HI

    Start-up window fogging prevention correction

  • The start-up window fogging prevention correction prevents the windows from fogging when all of the following conditions are met.

    • Right after engine start

    • Heater is operated

    • Air is blowing from vents for defrosting

    Defroster correction

  • When the airflow mode is set to the defroster, the defroster correction adds a correction +2 V to the blower motor applied voltage to increase airflow volume.

Airflow mode control
  • The airflow mode control drives the airflow mode actuator in conjunction with the MODE dial and the vehicle conditions, and switches the position of the airflow mode door.

  • The airflow mode control has automatic and manual controls.

  • The airflow mode automatic control performs the following correction.

    • Engine coolant temperature correction (warm-up correction)

    Airflow mode automatic control

  • The climate control unit determines the airflow mode based on the current air mix actuator opening angle.

    Airflow mode manual control

  • The climate control unit switches the airflow mode according to the operation of the MODE dial.

Airflow mode

Air vent

Vent

Center vent, side vent

Bi-level

Center vent, side vent, front heat

Heat

Side vent (low volume), front heat, side demister (low volume), defroster (low volume)

DEF/HEAT

Side vent (low volume), front heat, side demister, defroster

Defroster

Side vent (low volume), side demister, defroster

    Engine coolant temperature correction (warm-up correction)

  • The engine coolant temperature correction (warm-up correction) prevents cold air from coming out of the lower vents after engine start in winter.

  • The engine coolant temperature correction (warm-up correction) switches the airflow mode in conjunction with the increase in the engine coolant temperature.

Air intake control
  • The air intake control drives the air intake actuator and switches the air intake door position in conjunction with the operation of the MODE dial and the vehicle conditions.

  • The air intake control performs the following controls.

    • Air intake manual control

    • RECIRCULATE mode control under severe heat

    • FRESH control in defroster mode

    Air intake manual control

  • The climate control unit switches the air intake mode by the operation of the recirculate switch.

Air intake mode (recirculate switch operation)

RECIRCULATE indicator light

FRESH???RECIRCULATE

On

RECIRCULATE???FRESH

Off

    RECIRCULATE mode control under severe heat

  • When the vehicle is driven at a very low speed with the A/C on under severe heat conditions, the climate control unit may change the air intake mode from FRESH to RECIRCULATE automatically. Due to this, load on the A/C compressor is reduced.

  • When the air intake mode is switched to RECIRCULATE, the indicator on the RECIRCULATE switch turns on.

    FRESH control in defroster mode

  • The FRESH control in the defroster mode switches the intake mode to FRESH when the airflow mode is set to the defroster.

  • The FRESH control in the defroster mode improves the effect of defrosting by switching the air intake mode to FRESH.

  • The FRESH control in the defroster mode switches the air intake mode to FRESH even if the system was set manually to RECIRCULATE.

A/C compressor control
  • The A/C compressor control turns the A/C on/off based on the climate control unit operation and signals from each sensor.

  • The A/C compressor control has automatic and manual controls.

  • The A/C compressor automatic control performs the defroster correction.

    A/C compressor automatic control

  • The climate control unit determines the A/C compressor mode on or off based on the ambient temperature.

  • The climate control unit determines the A/C signal (magnetic clutch) on or off in conjunction with the air conditioner operation such as A/C compressor on mode or AUTO ECO mode.

  • In the A/C compressor on mode, the A/C signal (magnetic clutch) on/off is determined based on the ambient temperature and the temperature of the air passing through the evaporator.

  • In AUTO ECO mode, the A/C signal (magnetic clutch on or off) on or off is determined based on the ambient temperature calculation value and the temperature of the air passing through the evaporator.

  • The ambient temperature calculation value is calculated based on the ambient temperature, set temperature, and the cabin temperature.

  • When the ambient temperature is low, the A/C signal (magnetic clutch) off temperature is set lower to prevent window fogging.

    A/C compressor manual control

  • The climate control unit switches the A/C compressor mode on or off according to the operation of the A/C switch.

A/C mode (A/C switch operation)

A/C indicator light

OFF ??? ON

On

ON ??? OFF

Off

    Defroster correction

  • The defroster correction turns the A/C compressor mode on to prevent window fogging when the airflow mode is set to the defroster.

    A/C cut-off control

  • The PCM performs A/C cut-off control based on the input signal from the climate control unit and outputs an operation signal to the A/C relay (magnetic clutch).(See A/C CUT-OFF CONTROL [SKYACTIV-G 2.0].)

Sensor signal delay function
  • The amount of solar radiation, and the ambient and cabin temperatures may change due to factors such as direct and intermittent sunlight (traveling through a city or a highway tunnel), or radiant heat from the ground under parked vehicles as well as the opening and closing of doors.

  • If control was performed based exactly on these variations, the air conditioning function would be negatively affected and smooth control could not occur.

  • In order to prevent this, the climate control unit delays and smooths the input signals for solar radiation, and the ambient and cabin temperature as shown in the following figure, achieving stable control.

  • When the engine is restarted after being temporarily stopped, the ambient temperature sensor may detect a temperature higher than the actual ambient temperature.

  • To prevent this, if the engine coolant temperature is 55 °C {131 °F} or more, each control is performed based on the data for the ambient temperature before the engine was stopped that was stored in the climate control unit.

Fail-safe
  • If a malfunction is detected by the malfunction detection function, the fail-safe function performs the following controls to prevent an operation malfunction of the full-auto air conditioner system and malfunction of output devices.

Fail-safe function table

Part where malfunction is determined

Malfunction determined when ignition is switched ON

Ignition switched ON under malfunction condition

Ambient temperature sensor

Ambient temperature sensor input value is fixed at value right before malfunction

Ambient temperature sensor input value fixed at 15 °C {59 °F}

Passenger compartment temperature sensor

Passenger compartment temperature sensor input value is fixed at value right before malfunction

Passenger compartment temperature sensor input value fixed at 25 °C {77 °F}

Evaporator temperature sensor

Evaporator temperature sensor input value fixed at 0 °C {32 °F}

???

Solar radiation sensor

Solar radiation sensor input value fixed at value right before the malfunction

(Solar radiation sensor input value is 1450 W/m2 or more)

Solar radiation sensor input value fixed at 0 W/m2

ECT sensor

ECT sensor input value fixed at 85 °C {185 °F}

???

Air mix actuator (potentiometer)

Air mix actuator drive signal is stopped right after the malfunction is determined

  • However, fixed at MAX COLD when manually set temperature is at 15 °C or 60 °F and fixed at MAX HOT when manually set temperature is at 29 °C or 84 °F

Control based on ambient temperature (Reference: Graph 1)

  • However, fixed at MAX COLD when manually set temperature is at 15 °C or 60 °F and fixed at MAX HOT when manually set temperature is at 29 °C or 84 °F

Airflow mode actuator (potentiometer)

Airflow mode actuator drive signal is stopped right when the malfunction is determined

  • For manual operation, only vent or defroster mode is operable

Control based on ambient temperature (Reference: Graph 2)

  • For manual operation, only vent or defroster mode is operable

Air mix actuator (motor lock)

Air mix actuator drive signal is stopped right after the malfunction is determined

Resumes output of the air mix actuator drive signal normally for 20 s after the ignition is switched ON (engine off or on). After that, motor output is stopped if a malfunction is detected.

Airflow mode actuator (motor lock)

Airflow mode actuator drive signal is stopped right when the malfunction is determined

Resumes output of the airflow mode actuator drive signal normally for 9 s after the ignition is switched ON (engine off or on). After that, motor output is stopped if a malfunction is detected.

Block Diagram

System Wiring Diagram

Structural View

Operation

Airflow temperature control

1. Based on the signals (1) from each sensor which change according to the temperature setting dial operation and the vehicle conditions, the climate control unit performs airflow temperature determination (2) when the ignition is switched ON (engine off or on).

2. The climate control unit drives (3) the air mix actuator based on the results of the airflow temperature determination and corrections.

3. The climate control unit detects the current air mix actuator opening angle based on the potentiometer voltage (4).

4. The climate control unit compares (5) the target actuator opening angle with the potentiometer voltage.

5. When the potentiometer voltage differs from the target actuator opening angle, the climate control unit drives (6) the air mix actuator motor.

6. When the potentiometer voltage matches (7) the target actuator opening angle, the climate control unit stops (8) the air mix actuator motor.

Airflow volume control

1. When the ignition is switched ON (engine off or on), the BCM turns the blower relay on (1).

2. When the blower relay turns on, the blower fan controller goes on operation standby.

3. Based on the operation of the airflow volume control dial and the temperature setting dial, the airflow mode condition, and the signals from each sensor (2), the climate control unit performs airflow volume determination (3) when the ignition is switched ON (engine off or on).

4. The climate control unit sends a blower speed signal (4) to the blower fan controller based on the results of the airflow volume determination and the corrections.

5. The blower fan controller operates (5) the blower motor based on the blower speed signal.

Airflow mode control

1. Based on the MODE dial operation and the signals (1) from each sensor which change according to the vehicle conditions, the climate control unit performs airflow mode determination (2) when the ignition is switched ON (engine off or on).

2. The climate control unit drives (3) the airflow mode actuator based on the results of the airflow mode determination and corrections.

3. The climate control unit detects the current airflow mode actuator opening angle based on the potentiometer voltage (4).

4. The climate control unit compares (5) the target actuator voltage with the potentiometer voltage.

5. When the potentiometer voltage differs from the target actuator voltage, the climate control unit drives (6) the airflow mode actuator motor.

6. When the potentiometer voltage matches (7) the target actuator voltage, the climate control unit stops (8) the airflow mode actuator motor.

Air intake control

1. The climate control unit performs air intake mode determination (2) based on the signals (1) from the operation of the RECIRCULATE switch and the MODE dial and the PCM when the ignition is switched ON (engine off or on).

2. The climate control unit drives (3) the air intake actuator based on the results of the air intake mode determination and corrections.

3. When the air intake actuator moves to FRESH or RECIRCULATE, the motor locks (4).

4. If the motor locks and is under excessive load, the current flowing from the climate control unit increases more than the specification. (Lock current)

5. When the climate control unit detects lock current (5), it stops (6) the air intake actuator motor.

A/C compressor control

1. Based on the operation of each switch/dial and signals (1) from each sensor which change according to the vehicle conditions, the climate control unit performs A/C compressor mode determination (2) when the ignition is switched ON (engine off or on).

2. The climate control unit sends (3) the A/C signal to the PCM according to the result of the A/C compressor mode determination and corrections.

3. The PCM turns the A/C relay on (4) based on the A/C signal and the signals from each sensor which change according to the vehicle conditions.

4. When the A/C relay turns on, the magnetic clutch turns on (5).

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