Compressor HVAC: Testing and Inspection

Engagement signal for A/C Compressor Regulator Valve -N280-, checking

- Switch ignition off.
- Connect A/C control head to vehicle wiring harness.







- Disconnect harness connector on A/C compressor.
- Recreate connection to regulator valve between connector A and connector B, using adapter cable from V.A.G 1594 A connector test kit.

NOTE:







You can create an adapter cable for this test. E.g. use connectors A and B (part number 1J0 973 702 and 1J0 973 802 and relevant terminal contacts), two suitable sockets for connectors C and two 0.5sq mm diameter wires.







- Connect DSO-measuring cable VAS 5051/8 to two adapter cable.
- Measuring cable (signal wire) to terminal -2-.
- Measuring cable (shielded, ground) to terminal -1-.
- Select operating mode "Test instrument" on VAS 5051: DSO (Digital Storage Oscilloscope) on
- Setting 5V/Div =, 5ms/Div (5 volt DC voltage and 5 milli seconds per unit)
- Start engine
- Select preset temperature to "Lo" on A/C control head.
- Switch activation of A/C Compressor Regulator Valve -N280- on and off, by pressing the "Auto" and "Econ" button on the A/C Control Head - E87 -.

Depending on button pressed on A/C Control Head -E87- the oscilloscope displays:
- During operating mode "OFF" of "Econ" no square wave signal (the regulator valve is not activated).







- During operating mode "Auto" and temperature selection "Lo" a square wave signal with an impulse width -A- between 75% and 100% (the regulator valve is activated)

NOTE:
- The illustration shows a signal with a duty cycle ratio of approx. 80%.
- The impulse width -A- is dependent of the required cooling performance, the vehicle voltage etc. (via the width of range -A- the current is regulated through A/C Compressor Regulator Valve -N280- by the A/C Control Head -E87-.
- The signal distance -B- is always 2 milli seconds (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 selection on the A/C Control Head -E87- and measured surrounding conditions (duty cycle between 100% and greater than 30%, the regulator valve is so activated that the necessary compressor output is reached to attain the selected temperature).
- During operating mode "Auto" and temperature selection "Lo" the A/C Compressor Regulator Valve -N280- is activated in such a way that the maximum permissible current of 0.8 A flows through -N280- (maximum compressor output).
- In controlled operation, the activation period is dependent on the requested cooling performance, the vehicle voltage etc. The activation period is at least so long that an average current of 0.3 A flows.

Test step 7:

Sunlight Photo Sensor -G107-

Test Step 7.1 - 7.2:

Test Step 7.3 - 7.4:

Test Step 7.5 - 7.8: