If the A/C system in your eighth generation (2008, 2009, 2010, 2011, 2012, 2013, 2014 & 2015) Mitsubishi Lancer hasn’t been working as well any more or the air coming out of the vents smells a bit musty, you probably need to clean or change the cabin air filter element in the HVAC blower motor housing.
Mitsubishi Lancer A/C Cabin Air Filter Replacement Guide
