My trusty 760T wagon has suddenly quit blowing air through the various orifices. Fan motor blows, heater and A/C works etc. but the selector switch does not allow me to change from vent to heater to defrost etc. It appears to be stuck between floor and defrost but is not fully blowing air. Where do I start? I have the dash somewhat apart and have found the air flap actuator but I'm not sure how to determine if this is the problem.