The invention relates to the field of an air conditioning device of a passenger car, in particular to a full-fresh-air overhead air conditioner which comprises a fresh air inlet, a fresh air door, a return air inlet, a return air grille, an air supply outlet, a core body dust filter screen, a fresh air filter screen, a condensate fan, a core body of an evaporator, an evaporation fan and a motor of the fresh air door, and has the characteristic structure that the full-fresh-air overhead air conditioner further comprises a return air door mechanism, an overflow air door mechanism, a return air door motor and an overflow air door motor; the design of the oversized fresh air inlet is adopted, and the return air door mechanism and the overflow air door mechanism are added, so that three running modes including full fresh air, part fresh air and full return air can be realized; due to the design of water leakage prevention, a rotary shutter structure is respectively adopted by the fresh airdoor, a return air door and an overflow air door which are respectively controlled by three independent motors; and a fresh air filtering device and a return air filtering device are arranged. The full-fresh-air overhead air conditioner has the characteristics of energy conservation, environmental protection, high comfortableness and good technological efficiency.