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System control At high increasing pressure At high increasing pressure, the crystal is “deformed“ more, so the change of resistance is larger. The test voltage decreases proportionately. Pulse width modulated signal Microprocessor Voltage Test voltage Silicon crystal resistor 208 065 t p Pulse width signal The pulse width increases in proportion to the increasing pressure. Period duration 20 ms At a high pressure of 3.7 MPa 37 bar , the pulse width is 18 ms. This is equivalent to 90 of the period duration. Pulse width 18 ms 208 066 Using the digital memory oscilloscope of the new vehicle diagnosis system VAS 5051, it is possible to visualise the pulse width signal. 38 Disconnected safety switch in the In the refrigerant circuit with restrictor, the low refrigerant circuit with restrictor pressure and the high pressure are often monitored by two separate safety switches. Low pressure Air conditioner low pressure switch F73 switches off the compressor when the pressure drops below approx. 0.17 MPa 1.7 bar in the F73 refrigerant circuit, for example. This pressure drop can occur if the refrigerant level in the circuit is too low. The compressor is protected. High pressure Magnetic clutch high pressure switch F118 switches off the compressor when the pressure exceeds approx. 3.0 MPa 30 bar for example. The absolute values should always be regarded F118 as being system specific. 208 067 Coolant temperature switch with pilot lamp The compressor constitutes an additional load for the engine. t p To avoid overheating the coolant when the engine is under heavy load, e.g. when travelling uphill, the additional compressor load is switched off. For this purpose, the coolant temperature is 208 069 monitored additionally by a coolant temperature switch with a pilot lamp. The primary monitoring device is the coolant temperature sender with indi