Refrigerant Temperature Sensor: Description and Operation

Refrigerant Temperature Sensor G454, Function And Signal Utilization

CAUTION: The connection on which Refrigerant Temperature Sensor G454 is installed does not possess a valve, therefore Refrigerant Temperature Sensor G454 must only be removed with a discharged refrigerant circuit.

- Refrigerant Temperature Sensor G454 is not installed on all vehicles at this time, e.g. not installed on vehicles with 6 cyl. gasoline engine







- Refrigerant Temperature Sensor G454 - B - (with temperature dependent resistor) is installed into refrigerant line - C - (high pressure side of refrigerant circuit) between compressor and condenser.
- Measured value of Refrigerant Temperature Sensor G454 - B - is evaluated by the front Climatronic Control Module J255 only under certain conditions.

NOTE:
- In the refrigerant circuit, there is essentially a direct relationship between temperature and pressure, if there should be too little refrigerant in the refrigerant circuit (less than 50% of the specified capacity), the temperature in the refrigerant circuit rises more strongly than intended for this pressure when A/C system is operating.
- The front Climatronic Control Module J255 evaluates the temperature in the refrigerant circuit and switches the compressor off in the event the temperature rises above the value that was stored for this operating condition at the outside temperature currently measured.
- In addition to insufficient refrigerant, a soiled condenser or faulty actuation of the coolant fans may also be the cause for excessive refrigerant temperature.
- Refrigerant Temperature Sensor G454, removing and installing







- To prevent the compressor from switching off already when the maximum permissible refrigerant temperature is exceeded briefly (may occur under certain conditions of operation), the front A/C control head Climatronic Control Module J255 switches off compressor only if refrigerant temperature - A - rises above the temperature characteristic curve marked with - D - in the table a minimum of 30 seconds at the outside temperature - B - currently measured and under the operating conditions described below. Excessive refrigerant temperature is measured in several consecutive measurement cycles, compressor can no longer switch on (repair malfunction cause, check and erase DTC memory).
- Since on this vehicle the refrigerant pressure is not evaluated together with refrigerant temperature and depending on operating conditions it is possible that temperature in refrigerant circuit can also rise sharply for a brief period with a correctly charged system (e.g. running at Wide Open Throttle (WOT) at high outside temperatures), refrigerant temperature is evaluated only under certain operating conditions.

- Engine speed less than 1000 RPM)
- Compressor switched on for at least 2 minutes
- Passenger compartment temperature less than 40 degrees C
- Vehicle speed was greater than 50 km/h at least one time before each evaluation
- Vehicle speed is currently less than 5 km/h

NOTE:
- A new measurement cycle begins the next time the 50 km/h limit is exceeded
- If detected that the temperature characteristic curve - C - is exceeded in several measurement cycles, a DTC is entered in DTC memory as a warning of a possible malfunction.