Mazda 6. Manual - part 90

CONTROL SYSTEM 

U–33

U

A/C Compressor Automatic Control

•

The climate control unit determines A/C ON/OFF mode based on the ambient temperature. When A/C is in ON 
mode, an ambient temperature computation value is calculated based on the ambient temperature, set 
temperature, and temperatures from various sensors. This value is used to determine the temperature of the 
air passing through the evaporator. The temperature of this air determines whether the climate control unit 
turns the magnetic clutch (A/C signal) off or on. When the ambient temperature is high/low, the climate control 
unit lowers/raises the magnetic clutch off temperature. This improves cooling comfort.

.

Correction
Defroster correction

•

To improve defrost effect when the DEFROSTER switched on, select A/C mode and set the A/C signal ON/
OFF temperature is set at 5.0/4.0

°

C. However, when in ambient temperature correction, defroster correction 

does not take place.

Ambient temperature correction

•

When the ambient temperature is below –5

°

C {23

°

F}, this correction fixes the A/C compressor in OFF mode to 

protect the A/C compressor (that is, to prevent A/C compressor fluid compression). If the A/C switch is pressed, 
only the indicator will indicate; the A/C compressor will not operate.

Windshield mist prevention correction

•

To prevent the air blown from the defroster when the heater is started in winter from clouding the windows, the 
blower motor and the A/C signal output are switched off for 6 seconds after the ignition is turned to ON 
position. This control only operates if the airflow is in HEAT, HEAT/DEF, or DEFROSTER mode during airflow 
volume automatic control.

1

A/C switch

2

Set temperature

3

MODE switch

4

Ambient temperature

5

Cabin temperature

6

Sunlight intensity

7

Signals

8

Climate control unit

9

Output

10

A/C relay

11

A/C compressor

12

Operation

A6E8540T009

1

A/C mode ON/OFF decision

2

Ambient temperature

3

A/C  ON

4

A/C  OFF

5

A/C ON/OFF mode determination when A/C is in 
ON mode.

6

Varies with an ambient temperature computation 
value.

7

Evaporator temperature

8

A/C signal on

9

A/C signal off

U–34

CONTROL SYSTEM 

MAX COLD correction

•

When temperature is set to MAX COLD (temperature setting dial is turned to the left), the A/C signal ON/OFF 
temperature is at 5.0/4.0

°

C. However, when in ambient temperature correction, MAX COLD correction does 

not take place.

A/C Compressor Manual Control

•

A/C ON (A/C mode, ECO mode) or OFF mode is selected by operating the A/C switch.

A/C ON/OFF mode determination in A/C mode

.

A/C ON/OFF mode determination in ECO mode

.

End Of Sie

A/C mode

Operation condition

A/C ON MODE

A/C MODE (A/C display)

A/C compressor is set in ON mode
A/C compressor operates below evaporator freezing level so that the 
evaporator temperature is within a certain range

ECO MODE (ECO display)

A/C compressor is set in ON mode
Magnetic clutch operates at higher evaporator temperature level than 
manual A/C mode to reduce A/C compressor operation time and 
improve driving economy

A/C OFF MODE

A/C compressor does not operate

A6E8540T010

1

Evaporator temperature

2

A/C  ON

3

A/C  OFF

A6E8540T011

1

Varies with an ambient temperature computation 
value.

2

Evaporator temperature

3

A/C  ON

4

A/C  OFF

CONTROL SYSTEM 

U–35

U

SENSOR FAIL-SAFE FUNCTION

A6E854001044T09

•

If the input signals received from the sensors are abnormal, the climate control unit will assume a malfunction 
and fix the values for the temperature signals from the sensors as shown below to prevent abnormal A/C 
control.

End Of Sie

SENSOR SIGNAL DELAY FUNCTION

A6E854001044T10

•

Sometimes signals received from sensors will indicate abnormal readings. For example, intermittent or 
obstructed sunlight (when the vehicle is traveling on city streets or through highway tunnels) causes the sensor 
signals to be abnormal. When the vehicle is parked and the doors are opened/closed, sunlight intensity, 
ambient temperature, and cabin temperature signals may be interrupted or may vary suddenly and extremely 
due to heat radiation from the road. If control is carried out faithfully according to the signals input by the 
sensors, conditions in the passenger compartment may become uncomfortable and control will not be smooth. 
The climate control unit delays the input signals for sunlight intensity, ambient temperature, and cabin 
temperature. It then takes an average value of the readings it receives so that control remains stable, as shown 
below.

•

In winter, once the engine is stopped and then restarted and the temperature around the engine remains high, 
the ambient temperature sensor will detect the engine heat, therefore, the system controls do not operate 
according to the actual ambient temperature. To prevent this from happening, each control operates based on 
the ambient temperature data stored in the climate control unit prior to the engine being stopped, as long as the 
engine coolant temperature is 55 

°

Cor above when the engine is restarted.

.

End Of Sie

Sensor

Temperature fixed in case of malfunction

Cabin temperature sensor

25

°

C {77

°

F}

Ambient temperature sensor

15

°

C {59

°

F}

Water temperature sensor

85

°

C {185

°

F}

Evaporator temperature sensor

0

°

C {32

°

F}

Solar radiation sensor

0 W/m

2

 {0 kcal/m

2

·s}

A6E8540T012

1

Sunlight intensity delay (example)

2

Actual sunlight intensity

3

Sunlight intensity input

4

Time

5

Ambient temperature delay (example)

6

Actual ambient temperature

7

Ambient temperature input

8

Cabin temperature delay (example)

9

Actual cabin temperature

10

Cabin temperature input

U–36

CONTROL SYSTEM 

ON-BOARD DIAGNOSTIC FUNCTION

A6E854001044T11

Outline

•

Based on the sunlight intensity and temperature signals from the various sensors, the climate control unit 
performs very complex control to the output actuation devices. Therefore, the operating condition of the output 
devices may vary due to input conditions, even though the controls on the climate control unit are not changed. 
As a result, when a malfunction occurs in the control system, it may be difficult to reproduce the symptom and 
to isolate the malfunctioning part of the system. To avoid such difficulty, the climate control unit is programmed 
with a on-board diagnostic function which input system is malfunctioning. It can also check the output system 
separately from the input system.

•

The on-board diagnostic function has three modes: present failure indication, past failure indication, and output 
device operation check.

•

The climate control unit terminal 1F is connected to the body ground by the body grounding of the A/C check 
connector, whereby voltage fluctuation occurs. The climate control unit detects this voltage fluctuation and 
activates the on-board diagnostic function.

.

A6E8540T013

1

Normal  control

2

Warm up the engine

3

Turn the ignition switch to LOCK position

4

Short the A/C check connecotr to the body ground 
using a jumper wire

5

Light the solar radiation sensor with 60 W lamp at a 
distance 100 mm {3.9 in}

6

Start the engine

7

On-board diagnostic

8

Present failure indication

9

Diagnostic trouble code(s) indicated

10

A/C switch on

11

Past failure indication

12

Press REC/FRESH switch and AUTO switch at the 
same time

13

Past failure memory deletion

14

Rear defroster indicator light flashes once

15

AUTO switch on

16

Output device operation check

17

Check indicator lights illuminate for 4 seconds.

18

Step 1

19

Step 2

20

Step 3

21

Step 4

22

REC/FRESH switch on