My car was fitted with an auxiliary heater fan from new (shown on Heritage cert.] and still has it. Looking inside at the heater it appears to have a fan there as well which doesn't run when fan switched on, the one under he bonnet does-was this normal? I'll be removing the aux. fan to make more room under the bonnet and will 'reinstate' the inside fan.
Can't find any reference to auxiliary fans and have never seen another.