A/C System Signals, Checking
A/C System Signals, Checking
Special tools, testers, measuring instruments and auxiliary items required
- VAG 1551/1552 Scan Tool using VAG 1551/3 Adaptor cable
- VAG 1598/22 Test Box
- Fluke 83 multimeter
- VW 1594 Adaptor kit
- Wiring diagram
Checking requirements
- A/C function OK
- No malfunctions stored in DTC memory
- Vehicle temperature: +15 °C (59 °F) minimum
- A/C system switched ON
A/C compressor shut-off, checking
The A/C control head signals the Engine Control Module that the A/C compressor will be switched ON via the A/C compressor signal.
Using the same wiring, the A/C compressor is switched OFF by the ECM under the following circumstances:
- Hard acceleration from low speed
- Engine is running under an emergency program
- Engine Coolant Temperature exceeds +120 °C (248 °F)
- During every engine start for approx. 6 seconds.
Checking
- Connect VAG 1551/1552 Scan Tool.
- Start engine and let idle.
- Press 0 and 1 buttons to select Address word 01: "Engine electronics"
Display will appear as shown (example only)
038906018M 1.9l R4 EDC 00AG 1813 ->
Coding 0001 WSC XXXXX
- Press -> button.
Display will appear as shown
Rapid data transfer HELP
Select function XX
- Press 0 and 3 buttons to select Function 03: "Output Diagnostic Test Mode".
Display will appear as shown
Rapid data transfer Q
03 Output Diagnostic Test Mode (DTM)
- Press Q button to enter input.
Display will appear as shown
Output Diagnostic Test Mode (DTM) ->
Cold Start injector N108
Press -> button.
Display will appear as shown
Output Diagnostic Test Mode (DTM) ->
EGR valve N18
- Press -> button.
Display will appear as shown
- A/C compressor shut-off is checked via Output DTM.
- The A/C compressor must stop within 5 secs, (visual check) then start approx. every 5 secs. and then stop.
Output Diagnostic Test Mode (DTM) ->
A/C compressor interruption
If A/C compressor NOT switched OFF
- Proceed with Function 03: Output DTM, until completed.
- Press 0 and 6 buttons to select Function 06:" End output".
- Press Q button to enter input.
- Connect VAG 1598/22 Test Box to ECM wiring harness.
- Check wiring for open circuit between Test Box sockets 16 and A/C system using Wiring diagram.
- Wire resistance: 1.5 Ohms maximum
A/C system signal to ECM (engine speed adaption), checking
The A/C system signal ensures that the Engine Control Module maintains A/C system operation constant regardless of load at idle.
Test sequence
- Connect VAG 1551/1552 Scan Tool.
- Start engine and let idle.
- Press 0 and 1 buttons to select Address word 01: "Engine electronics"
Display will appear as shown (example only)
038906018M 1.9l R4 EDC 00AG 1813 ->
Coding 0001 WSC XXXXX
- Press -> button.
Display will appear as shown
Rapid data transfer HELP
Select function XX
- Press 0 and 8 buttons to select Function 08: "Read measuring value block".
- Press Q button to enter input.
Display will appear as shown
Read measuring value block HELP
Input Display group number XXX
- Press 0, 0 and 2 buttons to select "Display group 2"
- Press Q button to enter input.
Display will appear as shown (1 to 4 Display zones)
Read measuring value block 2 ->
1 2 3 4
- Switch ON A/C by pressing 'Auto" button and selecting lowest temperature.
- A/C compressor must run.
- Observe display in Display zone 3.
- Specified Value: 1 X 1 (A/C system signal)
Read measuring value block 2 ->
1 2 111 4
If specification not obtained
- Connect VAG 1598/22 Test Box to ECM wiring harness.
- Check wiring for open circuit between Test Box socket 48 and A/C system using Wiring diagram.
- Wire resistance: 1.5 Ohms maximum