2003 XC90 - CCM codes: air quality sensor: signal too low/too high

[Volvo Kush]

Vehicle: XC90 2003 2.9 T6
Problem: A/C clutch doesn't engage. (initial thread: http://goo.gl/nU3WiL )

Got my CMM codes read today:
CCM-001F air quality sensor: Signal too high
CCM-0020 air quality sensor: Signal too low
CCM-0004 compressor: Faulty signal

Where are these sensors located? I would want to attempt cleaning them before paying for the replacement.

Thanks in advance