A/C Compressor Regulator Valve (N280), Checking Switch-On Signal
A/C Compressor Regulator Valve (N280), Checking Switch-On Signal
• Perform the electrical test of the activation of the A/C Compressor Regulator Valve using the using the Vehicle Diagnostic Tester in the "Guided Fault Finding" function.
• The Vehicle electrical system control module (J519) actuates the A/C compressor regulator valve. The request to activate the A/C compressor regulator valve and the required current strength for regulating the compressor output to attain the desired temperature at the evaporator is sent via the data bus from the Climatronic control module (J255) , to the Vehicle electrical system control module. The Vehicle electrical system control module then activates the A/C compressor regulator valve.
• If a malfunction is detected in the activation of the A/C compressor regulator valve, an entry is made in the event memory of the Vehicle electrical system control module and the Climatronic control module. When reading out the event memory of the Climatronic control module, you will be prompted to query the event memory of the Vehicle electrical system control module using the Vehicle Diagnostic Tester in the "Guided Fault Finding" function.
• The activation of the A/C compressor regulator valve is displayed in "Read measured values" of the Vehicle electrical system control module using the Vehicle Diagnostic Tester in the "Guided Fault Finding" function.
• The A/C compressor regulator valve is only present for mechanically driven A/C compressors.
Test Sequence
- Remove the noise insulation - 1 -.
- Disconnect the electrical harness connector - B - at the A/C compressor regulator valve.
- Using an adapter cable from the Connector test kit (V.A.G 1594 C) recreate the connection between terminal - A - and terminal - B - on the A/C Compressor Regulator Valve.
• The figure shows a 4 cylinder and 6 cylinder engine. Depending on the engine, the arrangement of the connector for the A/C Compressor Regulator Valve at the A/C compressor can differ.
• The A/C compressor regulator valve is activated by the Vehicle electrical system control module (J519) upon request from the Climatronic control module (J255). Check using the Vehicle Diagnostic Tester in the "Guided Fault Finding" function.
• The above figure shows an A/C compressor where connector - A - to the vehicle wiring harness is connected directly to the A/C compressor regulator valve (connector - B -). Depending on the version of the A/C compressor, the connector - B - may also have a short line (for example in an 8 cylinder TFSI engine).
• The activation of the A/C compressor regulator valve is displayed in the "Read measured values" function of the vehicle electrical system control module (J519) and the Climatronic control module. The maximum control current depends on the version of the Climatronic control module. Check using the Vehicle Diagnostic Tester in the "Guided Fault Finding" function and.
• The measured current flowing through the A/C compressor regulator valve is displayed in the "Read measured values" function of the Climatronic control module and in the "Read measured values" function of the Vehicle electrical system control module. Check using the Vehicle Diagnostic Tester in the "Guided Fault Finding" function.
• If the required actual current is not flowing through the A/C compressor regulator valve, check the positive and ground connections of the Vehicle electrical system control module and the wire connections between the Vehicle electrical system control module and the A/C compressor regulator valve for short circuit, contact resistance and interchanged wires according to the wiring diagram.
• An adapter cable can also be used for this test. To do this, for example, use one connector each - A - and - B - (part number 1J0 973 702 and 1J0 973 802 and relevant terminal contacts), two standard sockets for banana connectors - C - and two wires with a diameter of 0.5 mm 2.
- Connect the DSO Measuring Lead 1 & 2 (VAS 5051/8) to the adapter cables.
• Measuring lead (signal wire) to terminal - 2 - of connector - B -
• Measuring lead (shielding, Ground) to terminal - 1 - of connector - B -
- Set the measuring equipment: DSO (digital storage oscilloscope) operating mode on the vehicle diagnostic tester.
- Select the setting 5V/div = 0.5ms/div (5V DC and 0.5 milliseconds per unit).
- Start the engine.
- On the Climatronic control module (J255) , set the temperature preselection to "LO" (maximum cooling output).
- Press the AC button on the Climatronic control module to switch the activation of the A/C compressor regulator valve on and off.
The following is displayed on the oscilloscope screen depending on the Climatronic control module setting:
• In operating mode "OFF" or "AC off" (indicator lamp in the AC button does not illuminate), there is no square wave signal (the A/C compressor regulator valve is not activated).
• In operating mode "Auto" and "AC on" (indicator lamps in the AC buttons illuminate), there is a square wave signal with an impulse width - A - between 75% and 100% (the control valve is activated).
• The Fig. shows a signal with a duty cycle of approximately 80%.
• Impulse width - A - depends on the desired cooling output, vehicle voltage, etc. (over the width of region - A -, the voltage is regulated via the A/C compressor regulator valve by the Vehicle electrical system control module on the basis of the request from the Climatronic control module).
• The signal distance - B - is always 2 milliseconds (corresponds to frequency of 500 Hertz).
• The duty cycle is determined by the ratio of impulse width - A - and signal distance - B -.
- The impulse width of the square-wave signal changes (duty cycle between 100% and greater than 30%, the A/C compressor regulator valve is activated so that the required compressor output is obtained to reach the specified temperatures) depending on the setting on the Climatronic control module and the measured environmental conditions.
• In the "Auto" and "AC on" setting (the indicator lamps in the AC buttons illuminate) and with a temperature preselection of "LO", the A/C compressor regulator valve is activated so that the maximum permissible current of approximately. 0.85 A flows through the A/C compressor regulator valve (maximum compressor output).
• In control mode, the duration of the activation depends on the required A/C output, the vehicle electrical system voltage, etc. The activation is at least long enough so that a mean current of 0.3A is achieved.