kirenh you put your blower in auto mode? sometimes the blow shifts patterns to cool the cabin. so the air coming from the lower vents is not an issue. now when you set the temperature to 24 hot air comes? these needs to be checked by a technician. the temperatures are not that different. 21 acc temperature, the cabin might be 23-24 and the temperature at the vents might be a little lower than 21.(my guesses) never checked the tempeature. Get the temperature in the compressor(or is it the condensor) if its less than 6degrees the cooling is optimum.