Audi Workshop Service and Repair Manuals

The air conditioner compressor signal informs the engine control unit that the compressor will be switched on in 140 ms.

The engine control unit can send a signal via the same wire to shut off the air conditioner compressor.

The engine control unit will shut off the air conditioner compressor in the following cases:

• ◆ On accelerating sharply from low speeds for approx 4 s (recognition from change in angle on throttle valve potentiometer and speed signal).
• ◆ At full load in 1st gear for a maximum of 12 seconds.
• ◆ If the throttle valve control unit is defective and the engine speed is less than 1500 rpm.
• ◆ After each engine start for approx 6 seconds.
• ◆ During the learning process for idle stabilisation for approx 15 seconds.

Test conditions

• ● Air conditioner functioning properly.
• ● No faults recorded in fault memory of engine control unit.
• ● Passenger compartment temperature warmer than +15 °C.

• ‒ Connect the V.A.G. 1551 fault reader .
• ‒ Start the engine.
• ‒ Select the function "Reading measured value block" (function 08) and Display Group 20 % Page.

• ‒ Observe readout in display zone 4.

• Specified value: Compr. OFF

• ‒ Switch on the air conditioner by pressing the "Auto" key. The compressor must run.

• Specification for display zone 3: A/C - high
• Specification for display zone 4: Compr. ON

• ‒ Abruptly floor the accelerator and release again (brief burst of throttle).

When the accelerator is floored quickly, the readout in display zone 4 should jump from "ON" to "OFF" for a few seconds (compressor shut off during acceleration).

If the display is not as described:

• ‒ Switch the ignition off.
• ‒ → Connect the V.A.G 1598/22 test box to the wiring harness for the engine control unit
  => Page 24-8.
• ‒ Test for an open circuit and short to earth or positive in the wiring from contact 8 on engine control unit to the air conditioner.

=> Current Flow Diagrams, Electrical Fault Finding and Fitting Locations binder

• ‒ If there are no faults in the wiring, check the operation of air conditioner.

=> Air conditioner; Repair Group 01; Self diagnosis for air conditioner