Heating and Air Conditioning: Description and Operation

In the air thermo sensor and the air inlet sensor, a negative characteristic thermistor which converts the temperature surrounding the sensors to a resistance value is used. The sensor power supply (5 V) of the automatic compressor control unit is applied to each sensor. The voltages at each terminal of the air thermo sensor (10) and the air inlet sensor (9) are divided by the resistance value of each sensor and by resistance inside the automatic compressor control unit.

By turning the air conditioning switch from OFF to ECONO or A/C, the operation mode of the compressor is switched over. If it is turned to the first level, it becomes the ECONO mode, and the voltage at terminal (3) of the air conditioning switch becomes battery voltage. Then, if it is turned to the second level, it switches to A/C mode and the voltage at terminal (4) of the air conditioning switch becomes battery voltage.

The output [terminal (1)] of the automatic compressor control unit occurs when the conditions listed below are satisfied.

1. Air conditioning switch is ON (in ECONO or A/C modes).
2. The temperature surrounding the air thermo sensor (air temperature of the evaporator blower) is 4 °C (39 °F) or more.
3. The temperature surrounding the air inlet sensor (evaporator inlet air temperature) is 4 °C (39 °F) or more.