High Pressure Sensor (G65), Checking Pressure Signal
High Pressure Sensor (G65), Checking Pressure Signal
• After the A/C compressor is switched off in this vehicle, it may take a relatively long time for the pressure on the high pressure side to decrease (the expansion valve(s) is/are cold, the pressure on the low pressure side increases quickly after deactivation, the expansion valve(s) closes/close and the refrigerant can only flow slowly to the low pressure side).
- Remove plenum chamber cover.
- Disconnect the connector - A -.
Connector assignment high pressure sensor
Terminal - 1 - ground
Terminal - 2 - signal output (square wave signal to Climatronic Control Module (J255) ).
Terminal - 3 - positive (terminal 75)
• With harness connector - B - disconnected, the compressor will not switch on.
• The high pressure sensor - A - is an electronic component, which creates a square wave signal, the duty cycle ratio changes with pressure in the refrigerant circuit.
Check the pressure signal from the high pressure sensor
- A - Pressure on the high pressure side in the refrigerant circuit in bar (absolute pressure)
- B - square-wave signal duty cycle
- C - Characteristic curve
• Climatronic control module switches on the compressor (by actuating A/C Compressor Regulator Valve (N280) ) as soon as no compressor shut-off condition is present.
• If the duty cycle is greater than 12% (absolute pressure corresponds to approximately 1.8 bar (26 psi)) and smaller than 87.5% (absolute pressure corresponds to approximately 32 bar), the pressure is within the permissible range.
• The compressor is not switched on if the duty cycle is smaller than 12% or greater than 87.5% (A/C Compressor Regulator Valve is not activated).
• The duty cycle and pressure calculated by the Climatronic control module is displayed in the measured value block using Vehicle diagnosis, testing and information system VAS 5051 in the "Guided Fault Finding" function.
• At absolute pressure, 0 bar corresponds to absolute vacuum. Normal ambient pressure equals approximately 1 bar absolute pressure (14.5 psi). 0 bar pressure corresponds to an absolute pressure of one bar on most pressure gauges (indicated by -1 bar below 0).
• Climatronic control module sends the request to switch on Coolant Fan (V7) to Engine Control Module (ECM) via the CAN-Bus system, ECM then switches on the coolant fans directly or via Coolant fan control module (J293) (depending on version, at a certain pressure in the refrigerant circuit or independent of pressure as soon as compressor is switched on).
• Climatronic control module sends the request for increased Coolant Fan speed via Comfort CAN-Bus system to Engine Control Module (ECM) with compressor activated, depending on pressure calculated in refrigerant circuit. The fan speed determined by the Climatronic control module is displayed in the measuring value block using Vehicle Diagnosis, Testing and Information System VAS 5051 in "Guided Fault Finding" function.
• The signal generated from High Pressure Sensor (G65) is also used to control the engine. Climatronic control module sends the information to the Engine Control Module (ECM) via the CAN-Bus system (the necessary torque to drive the compressor depends on the pressure in the refrigerant circuit). Depending on the version of the engine control module, the signal in the measured values block will be displayed as a duty cycle using Vehicle Diagnosis, Testing and Information System VAS 5051 in "Guided Fault Finding" function, (the A/C system and, depending on engine, the fuel injection and ignition system or the diesel direct injection and pre-glow plug system).
• Depending on the version of the Climatronic control module 127% for the signal duty cycle and 51 bar (740 psi) for the pressure in the refrigerant circuit will be displayed in the Climatronic control module measured values block if the pressure signal from the high pressure sensor is missing without an entry stored in the DTC memory. Check using Vehicle Diagnosis, Testing and Information System VAS 5051 in "Guided Fault Finding".
This pattern appears on oscilloscope screen (for example on diagnostic operation system (VAS 5051 A) ) when the following conditions are met:
- Ignition switched on (B+ at terminal 3 and Ground (GND) terminal 1 on High Pressure Sensor present)
- Oscilloscope settings: 5 V/div. DC (5V per unit DC) 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).
• To connect High Pressure Sensor, for example, measuring leads from connector test kit (V.A.G 1594 C) may be used.
• The display shows a signal that is transferred when the pressure in the refrigerant circuit is approximately 7 bar (101 psi), it corresponds to an approximate duty cycle of 25% (with compressor not engaged, an ambient temperature of 30 °C (86 °F)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 (corresponds to frequency of 50 Hertz).
• The duty cycle is determined by the ratio of impulse width - A - and signal distance - B -.