Upon arrival tech was informed of bacterial buildup on supply vents in part department as well as employees in this are that are getting sick during the work week. Tech inspected system and found challenges at RTU4. Tech removed supply vents from supply line in parts room and found inside of duct to be clean and registers to be insulated. Tech found system to be running in cool mode set at 68. If system is running in cool mode most of the year this will cause supply registers to condensate being there is warm air mixing with supply registers. Also thermostat is located in electrical room conditioned by a mini split. Tech recommended cleaning all supply registers and installing a Plasma Pure Air Purifier to improve air quality in this area. Quoted $881.45 plus tax for installation of Plasma Pure Air. Quoted $180.62 to clean supply registers (each). Mr. Danny cleaned the supply registers. Tech relocated thermostat per customer request from electrical room to parts department. Tech tested