Heating apparatus for motor vehicles

A heating apparatus for motor vehicles, comprising:

• an air flow passage provided with a first and second port which are adapted for taking in air from the vehicle compartment and for taking in air from outside the motor vehicle, respectively;
• an air intake door provided in said air flow passage in proximity to said first and second ports, said air intake door being arranged to selectively assume a first position to close said first port and open said second port for permitting the air taken in from outside the motor vehicles to be introduced into said air flow passage, a second position to open said first port and close said second port for permitting the air taken in from the vehicle compartment to be introduced into said air flow passage, and any intermediate position to open both of said first and second ports for permitting a mixture of the air taken in from outside the motor vehicle and the air taken in from the vehicle compartment to be introduced into said air flow passage;
• a heater core disposed in said air flow passage;
• a blower disposed in said air flow passage;
• and
• a heated air recirculation passage communicating with said air flow passage at a position upstream of said heater core and at a position downstream thereof, so that part of an air flow passed through and heated by said heater core to be used for heating the vehicle compartment is passed through said recirculation passage to be recirculated to a region upstream of said heater core.