A/C Switch
- When the A/C system is turned on, MCU should see battery voltage signal at pin No. 41 (Violet/Gray wire). At the same time, when the air conditioning 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:
- 3 & 5 Series - Check connection at low pressure cut-out switch of air conditioning system. Low pressure cut-out switch is located behind right side headlights.
- 635CSi - Check Black wire at evaporator temperature regulator. Evaporator temperature reguator is in passenger compartment, on left side of center console.
- 735i - Check Black/Red/Green wire at compressor relay.
- If battery voltage is not present at MCU pin No. 41 when A/C is turned on, check the following:
- 3 Series - Check Black/Violet wire at A/C control switch assembly.
- 5 Series - Check Violet/Green wire at A/C relay. A/C relay is in relay box on left side of engine compartment.
- 635CSi - Check Green/Yellow wire at A/C selector switch.
- 735i - Check Black/Blue/Yellow wire at A/C Motronic Relay. Check relay for proper operation. Relay is in auxiliary relay box.
NOTE:
On models with self-diagnostic system, a code 40 will be set if battery voltage is not read at both MCU pins No. 40 and 41 when A/C is turned on.