Expansion Valve: Testing and Inspection
A/C Compressor Regulator Valve, Checking Activation Signal
- Switch off ignition.
- Remove noise insulation.
- Mark connector - A -.
• In vehicles with an 8 cylinder engine, this connector is not installed at the compressor, but rather at the engine above the motor.
• In vehicles with an electric engine mount, ensure the proper allocation of connectors at the engine mount and at the A/C compressor regulator valve (N280), these components have the same connections. If the connectors are transposed, an error will not be stored (the components have approximately the same electric values), the engine mount will be actuated by the Climatronic Control Module (J255), and the A/C compressor regulator valve (N280) by the Engine Control Module.
- Disconnect connector - A - from socket - B - for the A/C Compressor Regulator Valve (N280).
- Reestablish the connection between connector - A - and connector - B - on A/C Compressor Regulator Valve (N280) 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) and measured by the Climatronic Control Module (J255) are displayed in the Climatronic Control Module (J255) measured value block => Vehicle Diagnosis, Testing and Information System VAS 5051 in the "Guided Fault Finding" function.
• An adapter cable can also be used for this test. To do this, e.g. 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 lead (signal wire) to terminal - 2 - of connector - A -
- Measuring lead (shielding, Ground) to terminal - 1 - of connector - A -
- In Vehicle Diagnosis, Testing and Information System (VAS 5051 A), select operating mode Test Instruments: DSO (digital storage oscilloscope), a => Vehicle Diagnosis, Testing and Information System VAS 5051 in the "Guided fault finding" function.
- Make the following setting at the Vehicle Diagnostic, Testing and Information System (VAS 5051 A): 5V/div = 0.5ms/div (5V DC and 0.5 milliseconds per unit)
- Start engine.
- At the Climatronic Control Module (J255) A/C control head, set the temperature preselect for the driver's and front passenger's side to maximum cooling (e.g., to temperature setting "Lo", or turn both rotary switches to the "cold stop" position).
- Switch on and off the controller of the A/C compressor regulator valve (N280) via the Climatronic Control Module (J255) A/C control head by pressing the Auto, Econ ON/OFF or A/C and ON/OFF buttons.
Shown on screen of oscilloscope, depending on setting of A/C control head Climatronic Control Module (J255):
- No square wave signal (A/C Compressor Regulator Valve (N280) is not activated) for operating mode "OFF" and "Econ" or "A/C off".
- A square wave signal with an impulse width - A - between 75% and 100% (A/C compressor regulator valve (N280) 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 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 depending on the Climatronic control module (J255) A/C control head setting and the measured environmental conditions (duty cycle between 100% and greater than 30%, the A/C compressor regulator valve (N280) is activated so that the compressor output necessary to reach the specified temperatures is achieved).
• For operating mode setting "Auto" and temperature setting "Lo" for example, the A/C Compressor Regulator Valve (N280) is activated such that the maximum permissible current of approximately 0.65 A flows via the 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.