Where does the condensate on the evaporator coil come from?

The condensate on the evaporator coil comes from the humidity in the air that is drawn into the HVAC system. As warm, moist air passes over the cold evaporator coil, the temperature of the air drops, causing the moisture to condense into water droplets. This process is similar to how dew forms on grass in the morning. The collected condensate is then typically drained away through a condensate drain line.