Compressor Control Valve Assembly: Testing and Inspection

A/C Compressor Regulator Valve, Checking Activation Signal

- Switch off ignition.

- Connect the Climatronic control module (J255) A/C control head to the vehicle wiring harness.

- Disconnect the connector from the A/C system compressor (to the A/C compressor regulator valve (N280)).





- Recreate the connection between connector - A - and connector - B - on the compressor (to the A/C compressor regulator valve (N280)) using an adapter cable from the connector test kit (V.A.G 1594C).

• 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 the adapter leads.

- Measuring cable (signal wire) to terminal - 2 -.

- Measuring cable (shielded, ground) to terminal - 1 -.

- In Vehicle Diagnosis, Testing and Information System (VAS 5051A), select operating mode Test Instruments: " DSO" (digital storage oscilloscope)

- Setting 5V/div = 0.5 ms/div (5 volts DC voltage and 0.5 milliseconds per unit)

- Start the engine.

- Set the temperature preselect for the driver's and front passenger's side to "Low" on the Climatronic control module (J255) A/C control head.

- Switch on and off the activation of the A/C compressor regulator valve (N280) via the Climatronic control module (J255) A/C control head by operating the " auto" and "econ" 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" or " Econ".

- 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 "Low".





• The Fig. shows a signal with a duty cycle of approximately 80%.

• Impulse width - A - is dependent on the desired cooling output, vehicle voltage, etc. (over the width of region - A -, voltage is regulated via A/C compressor regulator valve ( N280) by the Climatronic control module (J255 ) A/C control head).

• 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 " Low", the A/C compressor regulator valve (N280) is activated so that the maximum permissible current of approximately 0.6 A to 0.8 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.