A/C Signal: Testing and Inspection

NOTES:
- The A/C compressor is switched off (during acceleration by the Engine Control Module (ECM) and at wide open throttle by the Transmission Control Module (TCM) via the kickdown switch.

- A/C compressor shut-off is bi-directional ("in "and "out").

- IN: Shortly before switching the A/C compressor on, voltage is applied to the ECM which causes the Idle Air Control (IAC) valve to open a little more to adjust to the higher load.

- OUT: When accelerating from a stand still position and at lower speed, the A/C compressor is shut off for approx. 12 seconds via control by the ECM. If the accelerator pedal is released early enough, the duration is reduced to a minimal 3 seconds.

TEST CONDITIONS
^ A/C function OK.
^ No codes stored in DTC memory.
^ Vehicle at room temperature, i.e. warmer than 15°C (59°F).

TEST PROCEDURES
- Start engine and let idle.
- Switch A/C on, push "AUTO" button, set temperature to "LO" and blower speed to "HI."

Compressor symbol must light up.
A/C compressor must run.

- Using VAG 1551 scan tool, initiate "Basic Setting" function 04, display group 000,
A/C compressor must stop (check visually).


- Switch A/C off (press "minus" button for fresh air blower in A/C control head repeatedly, until all indicators are off), let engine continue to idle.
- Using VAG 1551 scan tool, initiate "Read Measuring Value Block" function 08, display group 004, refer to Diagnosis with Scan Tool, Address Word 01/Basic Setting/Display Group Diagnostic Charts Testing and Inspection
.

- Display will appear as shown:

Read Measuring Block Value 4 -->
1 2 3 4

NOTE: Do not use the shift inputs (identified by an X during the RPM in crease check.

- Switch on A/C as described.

Specified Value: X1X_XX.

If specified values are obtained:

- Press "arrow" button.
- Select "End Output" function 06.
- Press -Q- button to confirm input.

If display value changes:
- The following display is possible: "A/C system not switched on as described."

If the display value does not change, even though the A/C system was switched on as described:





- Check wiring for continuity between connector terminal C11 and ECM or TCM using wiring diagram.

If wiring is OK:
- Check A/C system or automatic transmission.

If "X1X XX" is displayed:
- Briefly push accelerator pedal to wide open throttle position.

Display must briefly change to XOX XX and, after releasing accelerator pedal, change back to X1X XX.

If the values change as described:
- Check whether compressor is switched off when depressing accelerator pedal suddenly (visual inspection).

If the compressor is not switched off:
- Check A/C system.

If the values do not change as described:
- Replace ECM.