Abstract: In an air conditioning system for a vehicle, a duct case has defined therewithin a cold-air passageway and a hot-air passageway. A heater is arranged within the duct case for heating air flowing through the hot-air passageway. An air-mixing damper is arranged for angular movement within the duct case at a location upstream of the heater, for adjusting flow rate of air passing through the cold-air passageway and flow rate of air passing through the hot-air passageway. A plurality of cold-air blowing openings open to the hot-air passageway at a location downstream of the heater. A cold-air bypass passage is provided for leading cold air before passing through the heater to the cold-air blowing openings. The cold air led by the cold-air bypass passage is blown from the cold-air blowing openings into flow of the hot air having passed through the heater such that the cold-air flow is intersected with the hot-air flow, thereby forcibly mixing the hot air and the cold air with each other.