Diagnostic and recirculation control systems and methods

A vehicle system, comprising

• a heating, ventilation, and air conditioning (HVAC) system including:
• a passenger cabin air filter;
• a blower;
• and
• a recirculation door configured to:
• when in a first position, allow the blower to draw air from outside of the passenger cabin through the passenger cabin air filter;
• and
• when in a second position:
• block airflow through the passenger cabin air filter to the blower;
• and
• allow the blower to air from within the passenger cabin to the blower;
• an olfaction sensor configured to measure an amount of a chemical in air upstream of the passenger cabin air filter;
• and
• a recirculation module configured to actuate the recirculation door to the second position when the amount of the chemical in the air upstream of the passenger cabin air filter is greater than a predetermined amount.