Today I arrived on site to address the reported smell issues on a carrier furnace unit located on the basement. Initial Assessment: Investigated the musty smell reported in the bedroom air vents connected to the AC and Heating system. Fault Confirmation: Confirmed there is not musty smell coming from the 1st floor air vent or 2nd floor aire vents as described by the client.Upon arriving at the property. The client mentioned that sometimes she perceives a musty smell in some air vents of the rooms on the second floor. The client directed me to the basement where the unit is installed. I immediately noticed that the client has two cat litter boxes in front of the unit. The client made room for me to verify the unit. I proceeded to verify the furnace unit. I didn't perceive any strange smell inside the unit. I proceeded to check the evap coil. The Evap coil is clean, I didn't notice any strange smell in the Evap coil either. I proceeded to run the system and monitor it. The sys