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Testing clutch pedal switch > < Testing signals from/to automatic gearbox

A4 Mk1

#Diesel direct injection and glow #plug system (4-cyl.)>06.97
Testing additional signals
Test signals from/to AC

Testing AC compressor cut-off

The engine control unit cuts out the AC compressor:

  • ◆ On rapid acceleration from low speed (detected via change in angle at accelerator position sender and by way of road speed signal)
  • ◆ In emergency program (limp-home mode)
  • ◆ If coolant temperature is more than 120 oC
  • ◆ After every start for roughly 6 seconds

Test prerequisites:

  • ● Air conditioner OK
  • ● No fault in fault memory
 
→ Perform final control diagnosis and actuate AC compressor engagement => Page .
Final control diagnosis    

The AC compressor must come to a stop within 5 s (visual inspection) and then start up and stop again every 5 s.

  • ‒ If the compressor does not come to a halt, connect up test box .
  • ‒ Test cable connection between test box, socket 28 and air conditioner for continuity/short circuit and repair if necessary.

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

Testing AC signal

The AC signal is only required on vehicles with automatic gearbox. On vehicles with manual gearbox, there is no cable connection for the AC signal.

The AC signal informs the engine control unit that the AC needs a higher idling setting to provide the necessary passenger compartment temperature (irrespective of whether cooling or heating is required).
 
→ Read measured value block (function 08) and select display group 02, engine idling
=> Page
Read measured value block 2     ⇒
820 rpm    0.0 %    0    1    0    18.4 oC
  • ‒ Switch on AC, press "Auto" button and select minimum temperature.
  • ‒ Check display in display field 3.
     
    → Desired value:
    X X 1 (AC compressor signal)
    Read measured value block 2     ⇒
    860 rpm    0.0 %    1    1    1    18.4 oC
    • ‒ If desired value is not attained, connect up test box => Page 23-37.
    • ‒ Test cable connection between test box, socket 37 and air conditioner for continuity/short circuit.

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

    Testing clutch pedal switch > < Testing signals from/to automatic gearbox