A/C Compressor Regulator Valve, Checking Switch-on Signal

A/C Compressor Regulator Valve, Checking Switch-On Signal

Special tools, testers and auxiliary items required

• Connector Test Set (V.A.G 1594C)

• DSO Measuring Leads 1 & 2 (VAS 5051/8)

• Vehicle Diagnosis, Testing And Information System (VAS 5051/)

Preparation

- Switch off ignition.

- Remove the front noise insulation - 1 -.

Test Sequence

• The A/C Compressor Regulator Valve (N280) activation and the current measured by the Climatronic Control Module (J255), which flows via the A/C compressor regulator valve, is displayed in the Climatronic control module measured values. Check using vehicle diagnosis, testing and information system VAS 5051 / under "Guided Fault Finding".

• 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 related terminal contacts), two standard sockets for banana connectors - C - and two wires with 0.5 mm 2 diameter.

V8 Vehicles:

- Disconnect electrical connector - B - on A/C compressor regulator valve - A -.

- Establish the connection between connectors - A and B - to the A/C compressor regulator valve using an adapter cable from the (V.A.G 1594C).

- Connect the (VAS 5051/8) to the adapter lines.

• Measuring lead (signal wire) to terminal 2 of connector - B -.

• Measuring lead (shielding, Ground) to terminal 1 of connector - B -.

For All Vehicles:

- Select the "Test instruments: DSO" (digital storage oscilloscope) on the (VAS 5051/).

- Then select the 5 V/Div = 0.5 ms / Div (5V DC and 0.5 milliseconds per unit) setting.

- Start the engine.

- Set the temperature rotary knob on the Climatronic control module to cold.

- Switch the A/C compressor regulator valve activation on and off by pressing the Auto and AC buttons.

Shown on the oscilloscpoe, depending on the Climatronic control module setting:

• There is no square-wave signal when OFF is selected (indicator light in the AC button is off (the A/C compressor regulator valve is not activated).

• With Auto selected and the AC button pressed (the indicator light in the AC button is on) there is a square-wave signal with an impulse width - A - between 75% and 100% (the A/C compressor regulator valve is activated).

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

• Impulse width - A - depends on the desired A/C output, vehicle voltage etc. (over the width of region - A -, voltage is regulated via the A/C compressor regulator valve by 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 depending on the Climatronic control module setting and the environmental conditions (duty cycle between 100% and larger than 30%, the A/C compressor regulator valve is activated so the compressor output necessary to reach the specified temperatures is achieved).

• With the Auto setting and the temperature rotary knob set to Cold for example, the A/C compressor regulator valve is activated so the maximum permitted current of approximately 0.65 A flows via 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.