What could cause this problem? on 2002 Chrysler Sebring

I sometime get cold air instead of heat coming out of the vents.I replaced the thermostat last year, just flushed the radiator and filled with new antifreeze. Sometime warm air might come out of 2 vents and cold out of the remaining vents.

Asked by for the 2002 Chrysler Sebring
Do you have dual heating controls? Double check the coolant level, make sure it is full.
Plenty of antifreeze. It has Temparture control and a heat, defrost, ac control.
Guess yours is not automatic with dual zone heat; Sounds like the temp/blend door actuator is malfunctioning.