Testing signals from and to air conditioner — AUDI

Testing engine speed regulation and compressor shut-off

Notes:

When the air conditioner is switched on a positive signal is sent to contact 8 on the engine control unit.
The signal causes the engine control unit to maintain a constant idling speed despite the varying power requirement of the air conditioner.
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 circumstances:
Sharp acceleration (full throttle)
In emergency running mode (back-up)
If the coolant temperature exceeds 120°C

Requirements for test:

Air conditioner okay
No faults stored in fault memory of engine control unit
Vehicle at room temperature
(above +15 °C)

Special tools, testers and auxiliary items

Fault reader V.A.G 1551 (or vehicle system tester V.A.G 1552) with cable V.A.G 1551/1
Adapter set V.A.G 1594 A
Test box V.A.G 1598/22

Connect fault reader V.A.G 1551
=> Page
01-2
.
Start the engine.
Select "Read measured value block", Display Group 020, engine at idling speed=>Page
01-137
.

Read measured value block
20
⇒
1
2
3
4
Indicated on display:

Switch off air conditioner.
Specification for display zone 4: "Compr.OFF"

Switch on the air conditioner by pressing the "Auto" key. The compressor should run.
Specification for display zone 1: The idling speed should remain constant. A brief drop in the engine speed (less than 1 second) is acceptable.
Specification for display zone 3: "A/C- High"
Specification for display zone 4: "Compr. ON"

Floor and release the accelerator quickly (short blip).

Specification for display zone 4: The display should change from "ON" to "OFF" for a few seconds (air conditioner compressor shut-off during acceleration).

If the displays are not as described:

Switch off ignition.
Connect test box V.A.G 1598/22 to wiring harness for engine control unit
=> Page
24-23
.
Test for open circuit and short to earth or positive in wiring between air conditioner and contact 8 on engine control unit using the current flow diagram.

=> Current flow diagrams, Electrical fault finding and Fitting locations binder

If there are no faults in the wiring, test operation of air conditioner.

=> Heating, air conditioner; Repair group 01; Performing self-diagnosis of fully automatic air conditioner
Heating, air conditioner
Performing self-diagnosis of fully automatic air conditioner

Testing air conditioner requirement signal

Note:

The air conditioner requirement signal tells the engine control unit that the idling speed must be increased so that the air conditioner can produce the desired interior temperature (regardless of whether warm or cold air is needed).

Special tools, testers and auxiliary items

Fault reader V.A.G 1551 (or vehicle system tester V.A.G 1552) with cable V.A.G 1551/1
Adapter set V.A.G 1594 A
Test box V.A.G 1598/22

Connect fault reader V.A.G 1551
=> Page
01-2
.
Start the engine.
Select "Read measured value block", Display Group 020, engine at idling speed=>Page
01-137
.

Read measured value block
20
⇒
1
2
3
4
Indicated on display:

Switch on air conditioner by pressing "Auto" key and select lowest temperature setting.
Specification for display zone 3: "A/C-High"

If the display is not as described:

Switch off ignition.
Connect test box V.A.G 1598/22 to wiring harness for engine control unit
=> Page
24-23
.

Test for open circuit and short to earth or positive in wiring between air conditioner and contact 10 on engine control unit using the current flow diagram.

=> Current flow diagrams, Electrical fault finding and Fitting locations binder