Checking signals from / to air conditioning system: Audi 2.8 (ACK, ALG)

ALG
Special tools,
testers and auxiliary items required

V.A.G 1594 A
V.A.G 1598/22
VAS 5051

or

V.A.G 1551 with V.A.G 1551/3 A

Checking engine speed adaptation 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 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 via the same wire to shut off the air conditioner compressor.
The engine control unit will shut off the air conditioning compressor in the following cases:
In the event of heavy acceleration (full throttle)
In the emergency programme (emergency running mode)
If the coolant temperature is more than 120°C

Test requirements:

Air conditioning system OK
No faults recorded in fault memory of engine control unit
Vehicle at room temperature (warmer than + 15 ° C)

Test sequence

Connect fault reader V.A.G 1551 => Page
01-2
.
Read measured value block, Display Group 020, Engine idling =>Page
01-147
.

Read measured value block 20
⇒
1
2
3
4
Display readout:

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

Switch on the air conditioner by pressing the "Auto" key. The compressor must run.
Specification for display zone 1: Idling speed must remain constant (brief drop in speed for less than 1 s is permitted).

Specification for display zone 3: A/C-high
Specification for display zone 4: Compr. ON

Abruptly depress the accelerator and release again (brief burst of throttle).
Specification for display zone 4: Display switched for several seconds from "ON" to "OFF" (compressor shut-off on vehicle acceleration).

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
24-24
.
Use current flow diagram to check for open circuit and short to earth or positive in wiring between contact 8 on engine control unit and air conditioner.

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

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

=> Air conditioner; Repair Group 01; Self-diagnosis for air conditioner
Air conditioner
Self-diagnosis for air conditioner