One point of clarification:
The 'demons' in the system when you do NOT explicitly set a mode (defrost, bi lev, feet, etc) is that the system tends to :
When its cold out - the system will blow cold air on the windshield until the car engine is warmed, then it will swtich modes to blow the warm air on your feet. it will then, as it approaches temperature, switch to bi-lev with cooler air to ease into the desired temerature. it will also vary fan speed.
This is true for any mode in which you did NOT explicitly set the output.