Refrigerant Pressure Sensor / Switch: Testing and Inspection
Pressure Signal Of High Pressure Sensor G65, Checking
- Remove radiator grille.
- Disconnect connector - A -.
Connector assignment at High Pressure Sensor G65
Contact 1 ground
Terminal 2 signal output (square wave signal to Climatronic Control Module J255)
Contact 3 Positive (terminal 75)
NOTE:
- With harness connector - B - disconnected, the compressor will not switch on.
- High pressure sensor - A - is an electronic control module; it creates a square wave signal, the duty cycle ratio changes with pressure in the refrigerant circuit.
Pressure signal from High Pressure Sensor G65
A Refrigerant system pressure, high pressure side in bar (absolute pressure)
B Signal ratio of square wave signal
C Characteristic curve
NOTE:
- Climatronic Control Module J255 switches on compressor (by actuating A/C Compressor Regulator Valve N280) as soon as no compressor shut-off condition is present:
- If duty cycle is greater than 12 % (corresponding to approx. 1.8 bar absolute) and less than 87.5% (corresponding to approx. 32 bar absolute)
- The compressor is not switched on if the duty cycle is smaller than 12 % or greater than 87.5% (A/C Compressor Regulator Valve N280 is not activated).
- Duty cycle and pressure calculated by Climatronic Control Module J255 is displayed in measured value block (display group "001") Vehicle Diagnosis, Testing and Information System VAS 5051 in "Guided Fault Finding" function.
- In terms of absolute pressure, 0 bar corresponds to an absolute vacuum. Normal ambient pressure equals approx. 1 bar absolute pressure. On the scales of most pressure gauges, 0 bar corresponds to an absolute pressure of one bar (can be seen from -1 mark below 0).
- The Climatronic Control Module J255 transmits request to switch on coolant fans to Engine Control Module (ECM) via Comfort data bus, ECM switches coolant fans on via coolant fan control module.
- As soon as compressor is switched on, irrespective of pressure in refrigerant circuit
- Climatronic Control Module J255 transmits request for increased coolant speed via Comfort data bus to Engine Control Module (ECM) with compressor activated, depending on pressure calculated in refrigerant circuit. The fan speed determined by Climatronic Control Module J255 is displayed in the measured value block (display group "022") 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 J255 sends information to Engine Control Module (ECM) via the Comfort data bus (necessary torque to drive compressor depends on pressure in refrigerant circuit). Depending on engine control unit version, signal is displayed as duty cycle in measured value block. Vehicle Diagnosis, Testing and Information System VAS 5051 in "Guided Fault Finding" function.
This pattern appears on oscilloscope screen (e.g. 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 G65 present)
- Oscilloscope settings:5 V/div. DC (5 V per unit DC) 5 ms/div. (5 milliseconds per unit)
- Measuring lead (signal wire) connected to terminal "2" on High Pressure Sensor G65.
- Measuring lead (shielding) connected to terminal "1" (Ground -GND- on High Pressure Sensor G65).
NOTE:
- To connect High Pressure Sensor G65, e.g. 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, it corresponds to an approximate duty cycle of 25% (with compressor not engaged, an ambient temperature of 30 degrees 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 (corresponds to frequency of 50 Hertz).
- The duty cycle is determined by the ratio of impulse width - A - and signal distance - B -.