My passenger side fan doesn't come on. The other one kicks in when it should and the car stays cool in warm, sunny humid conditions.
Is one linked exclusively to the AC or should they come on in tandem? When I turn on the AC (for what that's worth) neither kick in.
Ultimately, the fans are both simultaneously controlled by the thermo fan switch. When the thermo fan switch is triggered, ground is applies to both fan relays via multiple power feeds in the fuse box. Hence, both fans turn on. The AC relay works independently of the thermo fan switch and triggers (per the wiring diagram) the RH fan when the AC is engaged. The entire 308 series, Boxers and 328 cars use exactly this set-up.