Safety concept

The safety concept is intended to inhibit any system malfunction, particularly unintentional control operations, through the monitoring of signals and function-relevant parameters.

If faults are detected, the system is switched over or shut down depending on the components concerned. The driver is informed of any faults by the display, and detected faults are stored for diagnostic purposes.

In order to ensure high system availability, existing faults, as far as possible, are cleared with terminal 15 ON.

This is done by resetting the logistics counter to zero. However, the fault memory content in the EEPROM is retained and can be read out for diagnostic purposes. The system is then operational again. Fast fault detection means that existing faults are detected before control operations can take place.

Only lowering is permitted if:

• the power supply voltage drops below the permissible minimum of 9 volts.
• the permissible compressor duty periods, and therefore compressor temperatures, based on a temperature duty period algorithm* are exceeded.

A reset is carried out if the voltage is within the required range of 9 to 16 volts or after expiry of the compressor pause period of approximately 100 seconds.<

Only raising is permitted if:

• The permissible control down period of 40 seconds is exceeded.
• The reset takes place the next time the vehicle is driven or after the next control-up procedure.

No control if:

• The permissible supply voltage of 16 volts is exceeded.

The reset takes place as soon as the voltage is within the required range.

* Temperature duty period algorithm: 

In order to prevent overheating problems when the compressor is running or when outside temperatures are very high, a temperature duty period algorithm has been implemented.

T_Start (starting temperature) is assumed from the coil resistance of the exhaust valve and the theoretical temperature change is calculated on the basis of the change in coil resistance.