High Pressure Safety Valve HVAC: Testing and Inspection
A/C Compressor Regulator Valve, Checking Activation Signal
- Switch off ignition.
- Unplug connector at air-conditioner compressor.
- Reproduce the connection between connector - A - and connector - B - at regulator valve using an adapter cable from Connector Test Kit (V.A.G 1594 C).
• The activation of the A/C Compressor Regulator Valve (N280) and the current flowing via the A/C Compressor Regulator Valve (N280) is measured by the Climatronic Control Module (J255) front A/C control head is displayed in the control head measured value block Vehicle diagnosis, testing and information system VAS 5051 in "Guided Fault Finding" function.
• An adapter cable can also be used for this test. To do this, 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 0.5 mm 2 diameter.
- Connect DSO Measuring Leads 1 & 2 (VAS 5051/8) to adapter leads.
- Measuring cable (signal wire) to terminal - 2 -.
- Measuring cable (shielded, ground) to terminal - 1 -.
- On Diagnostic Operation System (VAS 5051 A), set measurement mode: DSO (Digital Storage Oscilloscope)
- Setting 5V/Div = 0.5 ms/Div (5 volts DC and 0.5 milliseconds per unit)
- Start engine.
- Set pre-select temperature to "Lo" on front A/C control head Climatronic Control Module (J255)
- Use the "Audio" and "Off/On" buttons on the Climatronic Control Module (J255) front A/C control head to switch the activation of the A/C Compressor Regulator Valve (N280) on and off.
Shown on screen of oscilloscope, depending on setting of front A/C control head Climatronic Control Module (J255):
- No square wave signal (regulator valve is not activated) for operating mode "OFF".
- A square wave signal with an impulse width - A - between 75% and 100% (regulator valve is activated) for operating mode "Auto " and temperature setting "Lo".
• The Fig. shows a signal with a duty cycle of approximately 80%.
• Impulse width - A - is dependent on desired cooling performance, vehicle voltage etc. (over the width of region - A -, voltage is regulated via A/C Compressor Regulator Valve (N280) by front A/C control head Climatronic Control Module (J255)).
• 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%, regulator valve is activated so that required compressor output is obtained to reach the specified temperatures) depending on setting at front A/C control head Climatronic Control Module (J255) and measured surrounding conditions.
• For operating mode setting "Auto" and temperature setting " Lo", A/C Compressor Regulator Valve (N280) is activated so that the maximum permissible current of approximately 0.65 A flows via A/C Compressor Regulator Valve (N280) (maximum compressor output).
• In control mode, actuation time is governed by required cooling output and vehicle electrical system voltage, for example. It is however always of sufficient duration to achieve a mean current of 0.3 A.