it defaults to defrost if there is a problem! could also be the blend door motor not working! I'm in mississauga if you need a hand i would be glad to help! i have a bidirectional scan tool so i scan hvac and test motors in hvac to see if there working! would be glad to help another forum member...
i had a problem like that when i picked up my Z06 new only blowing cold air! if the blower is blowing on all speeds then its not the blower motor! they ad to reflash the hvac pcm! problem solved