Mazda Training manual — part 289

AIR CONDITIONING
SG02 - Control System [Manual Air Conditioning]

SG02-7

TC070-15-01H

Evaporator temperature sensor

A/C signal on/off is controlled by the climate control unit turning the A/C signal
(magnetic clutch) on and off based on the temperature of the air passed through the
evaporator when both the A/C and fan switches are on. This keeps the evaporator
surface temperature within the specified range to prevent the evaporator from being
frosted.

Look at the chart below, Control Reference Value. The predetermined value “t1” must
be above freezing point. The difference between “t1” and “t2” are usually 2 – 3 ºC.

t1 =4.5, t2=5.5 (Mazda 3)

The difference value in temperature between “t1” and “t2” is referred as hysteresis
that prevents continuing repetition of changes ON and OFF at a specified
temperature.

Character of Evaporator Temperature Sensor

Temperature – Resistance Temperature – Voltage (PCM input)

AIR CONDITIONING
SG02 - Control System [Manual Air Conditioning]

SG02-8

TC070-15-01H

Look at both graphs, “Temperature – Resistance” and “Temperature – Voltage (PCM
input)” and read the resistance and voltage at each given temperature as below.

Resistance kilo-ohm, Voltage V at -10 ºC

Resistance kilo-ohm, Voltage V at 0 ºC

Resistance kilo-ohm, Voltage V at 10 ºC

Insert “higher” or “lower” in the blanks of the explanation below.

The higher temperature it senses, the resistance it creates, therefore the
CPU detects voltage.

Look at the wiring diagram below. The left one shows the circuit of evaporator
temperature sensor extracted from the control system wiring diagram. And the right
one is a rearranged diagram of the circuit.

The evaporator temperature sensor is grounded through the climate control unit. The
circuit operates with 5 V power supply. The voltage between the resister R and the
evaporator temperature sensor varies according to the temperature that the sensor
senses. The CPU detects this variation of the voltage (potential) which is equivalent
at the terminal N of the climate control unit.














What do you think is the voltage at the terminal N if the resistance of the evaporator
temperature sensor is 0 ohm?
V

What do you think is the voltage at the terminal N if the resistance of the evaporator
temperature sensor is infinity?
V

Apply the ohm’s low and calculate the constant value of the resister R’s resistance.

ohm

AIR CONDITIONING
SG02 - Control System [Manual Air Conditioning]

SG02-9

TC070-15-01H

A/C relay

A/C relay is classified as Type A as shown in the table below. Its function is to be
checked by measuring the continuities.







*

* It requires supplying battery voltage.

Magnetic clutch

Mazda 3 [Z6, ZY] Mazda 3 [LF, L3]

1. Bolt
2. Pressure plate
3. Shim
4. Snap ring
5. A/C compressor pulley
6. Screw
7. Clamp
8. Screw
9. Stator and thermal protector
10. A/C compressor body

1. Bolt
2. Pressure plate
3. Shim
4. Snap ring
5. A/C compressor pulley
6. Snap ring
7. Screw
8. Clamp
9. Stator and thermal protector
10. A/C compressor body

AIR CONDITIONING
SG02 - Control System [Manual Air Conditioning]

SG02-10

TC070-15-01H

A bimetallic (Indirect sensing type) type thermal protector is shown in the figure below.

1. Thermal protector

Mazda 3



Magnet clutch function can be checked by directly applying the battery voltage as
shown in the figure below.