Audi Workshop Service and Repair Manuals

Testing air conditioning compressor signal and air conditioning compressor shut-off

The air conditioning 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 to shut off the air conditioning compressor via the same connection.

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

• ◆ During strong acceleration from low road speed for approx. 4 s (recognition from angle change at throttle valve potentiometer and road speed signal).
• ◆ At full load in 1st gear for approx. 12 seconds.
• ◆ If the throttle valve control unit is defective and the engine speed is less than 1500 rpm.
• ◆ After every start, for approx. 6 seconds.
• ◆ During the learning process for idle stabilisation for approx. 15 s.

Test conditions

• ● Air conditioning system OK
• ● No fault stored in fault memory

• ‒ Read measured value block, Display Group 20, engine at idling speed

• ‒ Observe readout in display zone 4.

• Specified result: Compr. OFF

• ‒ Switch on air conditioning system.

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

If specified result is not attained:

• ‒ Connect the V.A.G 1598/22 test box to the wiring harness for the engine control unit.
  .

The following wiring connections should be checked for open circuits and/or short to positive or negative:

• ‒ Rectify short circuit or open circuit if necessary.