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Testing speed signal > < Testing auxiliary signals

A4 Mk1

TDI diesel injection and glow plug system (4-cyl.) 08.99 ä
Testing auxiliary signals
Testing signals from and to air conditioner

Testing air conditioner compressor shut-off

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

Test conditions

  • ● Air conditioner OK
  • ● Air conditioning system switched on
  • ● No faults recorded in fault memory
 
→ Start final control diagnosis and activate conditioner compressor interruption .
Final control diagnosis    

The air conditioner compressor should cut out within 5 seconds (visual check), then start and stop again every 5 seconds.

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 23-47.

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

Test box V.A.G 1598/31, socket

Air conditioner operating and display unit, contact

29

=> Current flow diagrams, Electrical fault finding and Fitting locations binder
  • ‒ Rectify any open/short circuit as necessary.

Testing air conditioner signal

The air conditioner signal informs the engine control unit that the air conditioner needs a higher idling speed in order to provide the desired interior temperature (both when cooling and when heating).

The increase in idling speed resulting from the air conditioner signal depends on the control unit version and is not activated in all vehicles.

  • ‒ Read measured value block, Display Group 02, engine running at idling speed => Page 01-81
  • ‒ Observe display in display zone 3, the air conditioner must not be switched on.
 
→ Indicated on display:
Read measured value block 2    ⇒
    860 rpm    0.0 %    0    1    0    18.4 5C
  • ‒ Switch on air conditioner, press the "Auto" key and select the lowest temperature.
  • ‒ Select lowest temperature and highest blower speed. The air conditioner compressor must run.
  • ‒ Check display in display zone 3.
 
→ Specification: X X 1 (air conditioner compressor signal)
Read measured value block 2    ⇒
    900 rpm    0.0 %    1    1    1    18.4 5C

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 23-47.

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

Test box V.A.G 1598/31, socket

Air conditioner operating and display unit, contact

34

=> Current flow diagrams, Electrical fault finding and Fitting locations binder
  • ‒ Rectify any open/short circuit as necessary.

Testing speed signal > < Testing auxiliary signals