Hey guys have researched for weeks on end trying to work out why my heater isn’t working 2004 Ba xr6T, have checked connections with icc, heater core hoses are hot, hvac plugs are good no coolant leaks, only thing I can notice is I can’t see movement with the mixer shaft at all switching between ac and heat icc displays ac and everything works, how can I diagnose this issue is there a way to definitely confirm mixer shaft is broken or faulty hvac? Cannot confirm ac works as my pump is gone don’t wanna spend hundreds at mechanics just to diagnose , thanks legends