Refrigerant Temperature Sensor (G454), Function and Signal Utilization
Refrigerant Temperature Sensor (G454), Function and Signal Utilization
• The connection on which the Refrigerant Temperature Sensor is installed does not possess a valve, therefore Refrigerant Temperature Sensor must only be removed with a discharged refrigerant circuit.
Currently, the Climatronic control module (J255) does not use the measured value from the refrigerant temperature sensor to shut off the A/C compressor. If the vehicle has a refrigerant temperature sensor then the adaptation feature shuts off the temperature signal evaluation. Check using the Vehicle Diagnosis, Testing and Information System VAS 5051 in "Guided Fault Finding".
• The refrigerant temperature sensor was discontinued as of November 2007 as a running change. On vehicles with the Comfort A/C system, make sure the Climatronic control module for the Comfort A/C system is installed. Vehicles with a 6 cylinder TDI engine or an 8 cylinder engine but without a refrigerant temperature sensor may only have the Comfort front control and display unit installed (part number 4L0 820 043, beginning with index letter K). Refer to the Electronic Parts Catalog.
• If the vehicle has the Basis A/C system without a refrigerant temperature sensor, and the sensor is being displayed as a fault, then perform an adaptation to the Basis front A/C control head. It is not necessary to perform this on the Comfort A/C system because it has different versions of the front A/C control head. On the Basis A/C system, "Guided Fault Finding" displays the fault because the refrigerant temperature sensor is missing and the evaluation of the sensor is switched off (by entering in "adaptation"). Refer to Vehicle Diagnosis, Testing and Information System VAS 5051 in "Guided Fault Finding".
• Currently, the refrigerant temperature sensor is not installed in all vehicles (from start of production through the discontinuation as of 11.2007 on vehicles with a 6 cylinder TDI engine or an 8 cylinder engine).
• The measured value from the refrigerant temperature sensor is not evaluated by the Climatronic control module (adaptation has shut off the evaluating). The missing refrigerant temperature sensor will be stored as a fault because the vehicle is supposed to have a refrigerant temperature sensor (solution: change the adaptation to Basis front A/C control head using the Vehicle Diagnosis, Testing and Information System VAS 5051 in "Guided Fault Finding". Or, if the vehicle has a Comfort Climatronic control module, for example, connect a refrigerant temperature sensor , which is OK, to the vehicle wiring harness and secure it to the vehicle (without removing the faulty refrigerant temperature sensor and installing a new refrigerant temperature sensor).
• The refrigerant temperature sensor - B - (with temperature dependent resistor) is installed into refrigerant line - C - (high pressure side of refrigerant circuit) between compressor and condenser). For removing and installing, refer to => [ Refrigerant Temperature Sensor ] Refrigerant Temperature Sensor (G454).
• The Climatronic control module evaluates the measured value from the refrigerant temperature sensor - B - only under certain conditions, even if adaptation is not switched off.
• 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 Climatronic control module 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, removing and installing, refer to => [ Refrigerant Temperature Sensor ] Refrigerant Temperature Sensor (G454).
• 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 Climatronic control module 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 (for example, 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 °C (104 °F)
- Vehicle speed was greater than 50 km/h (31 mph) at least one time before each evaluation
- Vehicle speed is currently less than 5 km/h (3 mph)
- Evaluation by adaptation not switched off.
• A new measurement cycle begins the next time the 50 km/h (31 mph) 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.