Control functions and principles of automatic air conditioning

Control functions and principles of automatic air conditioning

A necessary outlet temperature (TAO)

TAO is the blower air temperature necessary to keep the temperature inside the car at the set temperature. This is calculated by the air conditioner ECU according to the state of the temperature control switch or control lever and the signals from the sensors (ie, the interior temperature sensor, the outside air temperature sensor, and the solar sensor).

According to this TAO, the air conditioner ECU causes the automatic air conditioner amplifier to output the drive signal to the servo motor and the blower motor to realize the operation of the automatic control system (except the compressor control).



Outlet temperature control chart


If the temperature control switch or control lever is placed in the MAX COOL (maximum cold air) or MAX WARM (maximum warm air) position, the microcomputer adopts a fixed value without calculation. This is done to increase sensitivity.

Two temperature control

1 Configuration

The temperature control system includes components such as an air temperature sensor inside the car, an air temperature sensor outside the car, a solar sensor, an evaporator sensor, a temperature setting resistor, an air mixing control servo motor, and an air mixing control servo motor amplifier. In microcomputer-controlled automatic air conditioners, programmable switches such as blower speed control switches have been eliminated.

2 Run

The microcomputer installed in the automatic air conditioner amplifier calculates the opening of the air mix control windshield based on the calculated TAO and the letter (TE) from the evaporator sensor. SW (opening signal) allows the air mixing control servo motor to determine the direction of the power supply, driving the air mixing control servo motor in the manner shown in Figure 1-4, thereby controlling the blower air temperature.


Temperature control operation diagram


(1) When SW is close to 0: When the calculated TAO and temperature signal TE from the evaporator sensor are almost equal, SW is close to 0. At this time, the microcomputer installed in the automatic air conditioner amplifier turns off TR1 and TR2, preventing the air mixing control servo motor amplifier from sending current to the air mixing control servo motor, thereby keeping the air mixing control windshield in the same position at that time.

(2) When SW is less than 0: When TAO is less than TE, SW <0, indicating that the air temperature of the blower needs to be reduced. At this time, the microcomputer installed in the automatic air conditioner amplifier turns on TR1 and turns off TR2. This allows the air mix control servo motor amplifier to send current to the air mix control motor, turning the motor to the COOL (cold) side, thereby moving the air mix control windshield to reduce the blower temperature. At the same time, the potentiometer installed in the air mixing control servo motor detects the angle that the air mixing control windshield has actually moved. If the value thus obtained is equal to the SW value, the microcomputer turns off TR1 to stop the servo motor.

(3) When SW is greater than 0: When TAO is greater than TE, SW> 0, indicating that the air temperature of the blower needs to be increased. At this time, the microcomputer installed in the automatic air conditioner amplifier turns off TRl and turns on TR2, so that the air mixing control servo motor amplifier sends current to the air mixing control servo motor, and the motor is turned to the WARM (hot) side, thereby moving the air Mixed control of windshield to increase the air temperature of the blower. At the same time, the potentiometer installed in the air mixing control servo motor detects the actually moved angle of the air mixing control windshield. If the obtained value is equal to the SW value, the microcomputer turns off TR2 to stop the servo motor.

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