Investigated residential AC unit emitting unusual odor. Conducted thorough inspection of system components. Discovered significant microbial growth on evaporator coil, causing "dirty sock syndrome." Performed deep cleaning of coil using self-rinsing, alkaline-based cleaner. Applied EPA-registered biocide treatment to prevent future growth. Cleaned condensate drain line and installed P-trap to maintain proper drainage. Replaced contaminated air filter with MERV 11 pleated filter. Verified proper refrigerant charge and airflow. System now operating efficiently with improved indoor air quality and elimination of offensive odor.