Abstract: An air conditioning unit includes a control that operates in an automatic air filtration mode of operation when commanded to do so. The control, when in this mode of operation, automatically activates an air filtration system within the unit in response to the sensing of contaminants in the air surrounding the unit. The automatic activation of the air filtration system occurs in response to an unfavorable comparison of a sensed value of air quality with an allowable limit for air quality. The allowable limit for air quality may be computed as a function of time so as to reduce the air quality required during times in which the space being heated or cooled is unoccupied.