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

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