1. Field of the Invention
The present invention relates to an air conditioning system, and more particularly to an air conditioning system suitable for use in vehicles.
2. Description of the Prior Art
A typical conventional air conditioning system, for example, a typical conventional air conditioning system for vehicles is constituted, for example, as shown in FIG. 8. A refrigerant such as freon gas is circulated in circulation route 1 formed from pipe 2. Compressor 3, condenser 4, expansion valve 11 and evaporator 5 are provided in circulation route 1 in this order in the circulation direction of the refrigerant which is shown by arrow "A". The endothermic surface of evaporator 5 is exposed to the interior of the vehicle (not shown). After the refrigerant is compressed by compressor 3, the refrigerant is transformed in phase from a high-pressure gas to a high-pressure liquid in condenser 4 and further to a low-pressure gas as it passes through expansion valve 11 and evaporator 5. When the refrigerant is transformed from liquid phase to gaseous phase (vapor phase) by evaporator 5, the refrigerant absorbs heat from the interior of the vehicle and the vehicle interior is cooled. Expansion valve 11 is provided between condenser 4 and evaporator 5. Expansion valve 11 reduces the pressure of the refrigerant to a relatively low pressure so that the liquefied high-pressure refrigerant can be easily vaporized when it passes through evaporator 5.
Compressor 3 is driven by engine 6 of the vehicle via pulley 6A, V belt 8 and pulley 7A attached to electromagnetic clutch 7. Electromagnetic clutch 7 controls the drive of compressor 3. Electromagnetic clutch 7 is initially controlled by an air conditioner switch (not shown). When the air conditioner switch is turned "on", electromagnetic clutch 7 is actuated and compressor 3 is driven by engine 6.
A receiver tank 9 is provided in circulation route 1 at a position between condenser 4 and evaporator 5. Receiver tank 9 temporarily stores the refrigerant which has been in a liquid phase. On top of receiver tank 9, an inspection hole 9A is provided for observing the liquefaction of the refrigerant. Pressure sensor 10 is attached to receiver tank 9. Pressure sensor 10 detects the pressure of the refrigerant in receiver tank 9. When the pressure in receiver tank 9 exceeds a predetermined pressure, a signal is sent to a control unit (not shown). The control unit sends an "off" signal to clutch 7 when pressure sensor 10 detects an excessive pressure, and the clutch is released and compressor 3 is stopped. The bursting of pipe 2 or other components can thus be prevented by stopping compressor 3. When the pressure of the refrigerant reduces to another predetermined pressure from the excessive pressure, pressure sensor 10 sends a signal to the control unit. The control unit sends an "on" signal to clutch 7, and compressor 3 is driven again. This on-off operation of compressor 3 in accordance with the detection of the pressure of the refrigerant by pressure sensor 10 is automatically controlled. Damage to pipe 2 or other components and the overheating of compressor 3 can be prevented by this control.
In such a conventional air conditioning system, there are the following problems. For example, in a case where foreign materials intervene between the cylinder and the piston of compressor 3, the compressor may be locked In such a case, the refrigerant cannot circulate in circulation route 1, and the cooling ability of the system quickly decreases. The driver of the vehicle cannot determine whether the reduction of the cooling ability is caused by the lock up of compressor 3 or by the leakage of the refrigerant. Therefore, in the conventional air conditioning system, a rotation detecting sensor is attached to the outside of compressor 3, and the lock of the compressor is detected by the sensor.
In such a conventional air conditioning system, however, since the size and type of compressor 3 vary depending upon the type of vehicle, it is often necessary to reconstruct the compressor in order to attach the rotation detecting sensor to the outside of the compressor. The working or processing of the reconstruction of the compressor is very time consuming and costly.
Moreover, even if the rotation detecting sensor is attached to the compressor, refrigerant leakage cannot be detected.