Came out to address unwanted odors coming from HVAC equipment when system is running. Home has 2 zone 2015 Lennox 4ton Heat Pump. Checked air handler for signs of bacterial growth. Also verified size of all equipment and ductwork. Found no immediate signs of bacterial growth inside of air handler. However, found drain line has a vent that is capped off. Let customer know this is incorrect and a contributing factor to issue. Causes drain to flow water very slowly which in turn allows for the sitting water to produce more bacteria. Removed cap for better drainage. Drain has gunk building up inside of it. Found system is oversized for this home (1791 square feet) which in turn causes poor dehumidification. Made customer aware of this and how it affects performance and indoor air quality. Let him know main solution would be to talk with an install supervisor about downsizing and upgrading to multi-stage HVAC equipment for proper dehumidification. Current system is only one stage. Ideal for