Audi Workshop Service and Repair Manuals

Requirements for test:

• ● Air conditioner okay
• ● No faults stored in fault memory
• ● Vehicle at room temperature
  (above +15 °C)
• ● Engine at operating temperature.

Testing AC compressor signal

The engine control unit receives the information that the air conditioner will be switched on shortly via the air conditioner ready signal.

Test sequence

→ Display on VAS 5051:

• ‒ Read data block Display group 002, engine running at idling speed => Page 01-96.
• ‒ Check display in display zone -3-.
• ‒ Specification: 0 X 0

Note:

Display value "X" can be ignored during test procedure.

• ‒ Switch on air conditioner, press the "Auto" key and select the lowest temperature.
• ‒ Specification: 1 X 1
• ‒ Press the ◂ button to exit from the function "08 - Read data block".
• ‒ Select diagnosis function "06 - End output".
• ‒ Switch off ignition.

If the specification is not obtained:

• ‒ Connect test box V.A.G 1598/31 to wiring harness for engine control unit. Do not connect to the engine control unit itself.
  => Page 23-37.
• ‒ Test for open circuit and short to positive or earth in the following wiring connection:

• ‒ Rectify any open/short circuit as necessary.

Testing AC compressor shut-off

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

• ◆ Heavy acceleration from low speeds (control unit detects angle change at accelerator position sender -G79 and receives road speed signal)
• ◆ In the emergency programme (emergency running mode)
• ◆ If the coolant temperature rises above 120 °C
• ◆ For about 6 seconds after every engine start

Test sequence

• ‒ Switch on air conditioning system.
• ‒ Select the function "Final control diagnosis" and activate air conditioner compressor shut-off => Page 01-55.

• ◆ The air conditioner compressor should stop running within 5 seconds (visual check), and then start and stop repeatedly every 5 seconds.

• ‒ Finish off final control diagnosis.
• ‒ Select diagnosis function "06 - End output".

• ‒ Switch off ignition.

If the conditioner compressor is not switched off:

• ‒ Connect test box V.A.G 1598/31 to wiring harness for engine control unit. Do not connect to the engine control unit itself.
  => Page 23-37.
• ‒ Test for open circuit and short to positive or earth in the following wiring connection:

• ‒ Rectify any open/short circuit as necessary.