Inlet air control method for a vehicle HVAC system having an air quality sensor

An improved HVAC control method immediately closes an air inlet valve (44) to provide full cabin air recirculation when an outside air quality sensor (92) detects polluted air, and thereafter progressively re-opens the air inlet valve (44) at a determined rate when the air quality sensor (92) detects unpolluted air. Preferably, the air quality sensor quantifies the pollution level of the outside air, and the opening rate of the air inlet valve (44) is determined based on the detected pollution level. Following a high level of detected air pollution, the valve is re-opened at a relatively slow rate, and following a low level of detected air pollution, the valve is re-opened at a relatively fast rate (104).