The answer to 'how to maintain an air handler' is to regularly clean and inspect the unit to ensure it is operating efficiently and safely. This includes cleaning or replacing the air filter, checking the blower motor and fan, and cleaning the coils and condensate drain.
It's recommended to clean the air filter monthly and replace it every 3-6 months, depending on usage and indoor air quality. The blower motor and fan should be inspected annually for proper operation and any signs of wear. The coils should be cleaned every 6 months to remove dust and debris, and the condensate drain should be checked regularly to ensure it is flowing freely and not clogged.