Checking Pressure Signal From High Pressure Switch -G65-
Checking Pressure Signal From High Pressure Switch -G65-
The oscilloscope shows this display when the following conditions are met.
- Ignition switched on (B+ and Ground available at High Pressure Switch -G65-)
- Setting on oscilloscope:
5 V/Div. = (5V per unit DC voltage)
5 ms/Div. (5 Milli seconds per unit)
- Measuring lead (signal lead) connected to socket -7- of test box.
- Measuring lead (shielded wire) connected to socket -14- of test box (Ground (GND)).
NOTE:
- 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 C and properly filled refrigerant circuit)
- The impulse width -A- depends on the pressure in the refrigerant circuit (if pressure increases, area -A- is getting wider).
- The signal distance -B-is always 20 milli seconds (corresponds to frequency of 50 Hertz).
- The duty cycle is determined by the ratio of impulse width -A- and signal distance -B-.
Connector assignment at High Pressure Switch -G65-
Terminal 1: Ground (GND)
Terminal 2: Signal output (square wave signal to -E87-)
Terminal 3: B+ (terminal 75)
NOTE:
- With harness connector -B- disconnected, the compressor will not engage.
- The high pressure sensor -A- is an electronic control module, which 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:
- The A/C control head -E87- switches the compressor on as soon as no compressor cut-off condition exists (by activating the A/C Compressor Regulator Valve -N280-):
- If the duty cycle is greater than 12% (absolute pressure corresponds approx.; 1.8 bar), if smaller than 87.5% (pressure corresponds to approx.: 32 bar).
- 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).
- The duty cycle and the calculated pressure by A/C Control Head -E87- is displayed in the measuring value block (display group 001). Measuring Value Blocks (Function 08)
- At absolute pressure, 0 bar corresponds to absolute vacuum. Normal ambient pressure corresponds to approximately 1 bar absolute pressure. 0 pressure corresponds to an absolute pressure of one bar on most pressure gauges (indicated by -1 below 0).
- The A/C Control Head -E87- sends the request to switch on the coolant fans to the Engine Control Module (ECM) via the CAN-bus comfort system, the ECM switches via the coolant fan control module the coolant fans on.
- Independent from pressure in refrigerant circuit as soon as compressor is switched on.
- The A/C Control Head -E87- sends the request for increased coolant fan speed to the Engine Control Module (ECM) via the CAN-bus comfort system:
- Vehicles with gas engines request 100% fan speed currently at approx.: 26 bar pressure in the refrigerant circuit.
- The signal generated from High Pressure Sensor -G65- is also used to control the engine. The A/C Control Head -E87- sends the information to the Engine Control Module (ECM) via the CAN-bus comfort system (the necessary torque to drive the compressor depends on the pressure in the refrigerant circuit). The signal is displayed as duty cycle in measuring value block depending on ECM version.
Test step 6:
Activation for A/C Compressor Regulator Valve -N280-
Test Step 6.1:
Test Step 6.2:
Test Step 6.3:
