High Pressure Sensor / Switch: Testing and Inspection
High Pressure Sensor (G65), Checking Pressure Signal
• Vehicles with automatically regulated A/C system: Climatronic Control Module (J255) evaluates the signal from High Pressure Sensor (G65) and actuates the compressor via the A/C Compressor Regulator Valve (N280).
• Vehicles with manually regulated A/C system: A/C Control Module (J301) evaluates the signal from High Pressure Sensor (G65) and actuates the compressor via the A/C Compressor Regulator Valve (N280).
• The cooling output cannot be checked when the high pressure sensor is removed; the Climatronic control module / the A/C control module does not switch on the compressor. Check using Vehicle diagnosis, testing and information system (VAS5051B) in "Guided Fault Finding" function.
• Depending on the version of the high pressure sensor, an insufficient measuring value for the pressure in the refrigerant system will be sent by the high pressure sensor at low outside temperatures (lower than 5 °C) (even though the A/C system is OK and the refrigerant circuit is properly filled). In the A/C control module or in the Climatronic control module, part number 8P0 820 043 up to index AH can register in incorrect DTC memory entry at low outside temperatures (lower than 5 °C) (DTC memory entry: high pressure sensor "lower values not met"). If the fault is displayed as a sporadic fault at an outside temperature greater than 5 °C, calculated by the A/C system, and if the A/C function is OK, then clear the DTC memory (no additional steps are necessary).
• Different component locations depending on engine, high pressure sensor in vehicles with 2.0 L Diesel engine is installed not on refrigerant line from expansion valve to condenser but rather on refrigerant line from compressor to condenser
• Currently on 4 cylinder vehicles, it is possible to disconnect the high pressure sensor connector without have to remove any other components because the connector is accessible from above.
• After switching off the A/C compressor in this vehicle, it may take a relatively long time for the pressure on the high pressure side to decrease. This is because the expansion valve is cold and the pressure on the low pressure side increases quickly after shutting the compressor off, then the expansion valve closes and the refrigerant flows slowly to the low pressure side.
- Remove the noise insulation (for example, on 6 cylinder vehicles).
- Disconnect the connector - A -.
Connector assignment high pressure sensor (G65)
Terminal - 1 - ground
Terminal - 2 - signal output (square-wave signal to the Climatronic control module / to the A/C control module)
Terminal - 3 - positive (terminal 75)
• When connector - A - is disconnected, the A/C compressor will not switch on.
• The high pressure sensor - B - is an electronic control module, which creates a square wave signal, the duty cycle ratio changes with pressure in the refrigerant circuit.
The pressure signal from the high pressure sensor (G65)
- A - Pressure on the high pressure side in the refrigerant circuit in bar (absolute pressure)
- B - square-wave signal duty cycle
- C - square-wave signal duty cycle characteristic line
• The Climatronic control module / the A/C control module switches the compressor on, as long as there are no compressor shut-off conditions (by controlling the A/C compressor regulator valve (N280) ). Check using Vehicle diagnosis, testing and information system (VAS5051B) in "Guided Fault Finding" function.
• Depending on the version of the high pressure sensor, an insufficient measuring value for the pressure in the refrigerant system will be sent by the high pressure sensor at low outside temperatures (lower than 5 °C) (even though the A/C system is OK and the refrigerant circuit is properly filled). In the A/C control module (J301) or in the Climatronic control module (J255) , part number 8P0 820 043 up to index AH can register in incorrect DTC memory entry at low outside temperatures (lower than 5 °C) (DTC memory entry: high pressure sensor "lower values not met"). If the fault is displayed as a sporadic fault at an outside temperature greater than 5 °C, calculated by the A/C system, and if the A/C function is OK, then clear the DTC memory (no additional steps are necessary).
• If duty cycle is greater than 12% (corresponding to approximately 1.2 bar absolute) and less than 78% (corresponding to approximately 32 bar absolute).
• The compressor is not switched on if the duty cycle is smaller than 12% or greater than 78% (the A/C Compressor Regulator Valve (N280) is not activated).
• The duty cycle and the pressure calculated by the Climatronic control module / the A/C control module is displayed in the measured value block of the Vehicle diagnosis, testing and information system (VAS5051B) in "Guided Fault Finding" function.
• In terms of absolute pressure, 0 bar corresponds to an absolute vacuum. Normal ambient pressure equals approximately 1 bar absolute pressure. 0 bar pressure corresponds to an absolute pressure of approximately 1 bar on most pressure gauges (indicated by -1 below 0).
• The Climatronic control module / the A/C control module sends the request to increase the Coolant fan (V7) RPM to the engine control module via the Data bus regardless of the calculated refrigerant circuit pressure and when the A/C compressor is on. Depending on version with a certain pressure in the refrigerant circuit or not depending on pressure as soon as the A/C compressor is switched on. Request determined by the Climatronic Control Module (J255) / A/C Control Module (J301) is displayed in measuring value block (Read measured values block) and Vehicle diagnosis, testing and information system (VAS5051B) in "Guided Fault Finding" function.
• The request for the coolant fan is currently sent at the following duty cycle:
• Pressure in refrigerant circuit less than approximately 9 bar (6 bar when pressure was greater than 9 bar), no request.
• Pressure in refrigerant circuit greater than approximately 9 bar (6 bar) up to approximately 20 bar, request of 30 to 100% (depending on pressure).
• If the refrigerant circuit pressure is greater than 20 bar, a 100% request will be made.
• The signal generated from high pressure sensor is also used to control the engine. Climatronic control module / A/C Control Module sends the information to the Engine Control Module (ECM) via the CAN-Bus Comfort system (the necessary torque to drive the A/C control module depends on the pressure in the refrigerant circuit). Depending on version of ECM, the signal in the measured value block is displayed as the duty cycle using Vehicle diagnosis, testing and information system (VAS5051B) in "Guided Fault Finding" function (for respective ECM installed).
This pattern appears on oscilloscope screen (for example on Vehicle diagnosis, testing and information system (VAS5051B) when the following conditions are met.
- Ignition switched on (B+ at terminal 3 and Ground (GND) terminal 1 on High Pressure Sensor (G65) present)
- Making the adjustment on the oscilloscope: 5 V/Div. = (5 volt per unit DC voltage) 5 ms / Div. (5 milliseconds per unit)
- Measuring lead (signal wire) connected to terminal 2 on high pressure sensor.
- Measuring lead (shielding) connected to terminal 1 (Ground -GND- on high pressure sensor).
• The illustration shows the signal, which is sent when the refrigerant circuit pressure is approximately 7 bar. This conforms to a approximate 25% duty cycle. With compressor not engaged, an ambient temperature of 30 °C and properly filled refrigerant circuit.
• The impulse width - A - depends on the pressure in the refrigerant circuit (if pressure increases, area - A - gets wider).
• The signal distance - B - is always 20 milliseconds. This corresponds to frequency of 50 Hertz.
• The duty cycle is determined by the ratio of impulse width - A - and signal distance - B -.
• Use the measuring leads form the (V.A.G 1594/C) or an adapter lead for this test. To do this, e.g. use connectors - A - and - B - (part number 1J0 973 703 and 1J0 973 803 and relevant terminal contacts. Refer to Electronic Parts Catalog (ETKA)), two standard sockets for banana connectors - C - and three wires with 0.5 mm 2 diameter.
