A/C Switch
- When the A/C system is turned on, MCU should have a battery voltage signal at pin No. 41 (Violet/Gray wire). At the same time, when the A/C compressor is engaged, MCU receives a signal at pin No. 40 (Black/Gray wire). These signals tell MCU to adjust idle speed (if necessary).
- If battery voltage is not present at MCU pin No. 40 when compressor clutch engages, check the following:
- 325 Series, 525i & 535i - Check connection at A/C low pressure cut-out switch, located behind passenger's side headlights.
- 735i - Check Black/Red/Green wire at A/C compressor relay.
- If battery voltage is not present at MCU pin No. 41 when A/C is turned on, check the following:
- 325 Series - Check Black/Violet wire at A/C control switch assembly.
- 525i & 535i - Check Violet/Green wire at A/C relay, located in relay box on left side of engine compartment.
- 735i - Check Black/Blue/Yellow wire at A/C-Motronic relay, located in auxiliary relay box. Check relay operation.
NOTE:
On models with self-diagnostic system, a Code 40 will set if battery voltage is not read at MCU pins No. 40 and 41 when A/C is turned on.