1) Have HVAC unit serviced by a professional HVAC company before departing, this is called a clean and check.
2) Replace existing AC filter and purchase HVAC filter spares and place on top of washing machine. If return vent for the filter is in the ceiling, have a ladder in the area.
3) Black spots on the inside of filters nearest the coil, indicate that the air handler coil flutes might be blocked and water is leaking on the filter, see picture of mold on air handler.
4) Check and clean any black mold in, on or around the coil or PVC of the air handler.
5) Test and use while in residence your dehumidifiers to assure they are working correctly.
6) Check all closets for signs of mold.
7) Replace all smoke detectors and thermostat batteries at least once a year.
8) Place toilet brushes and cleaner by each toilet.
9) Plastic wrap the toilet bowls and leave plastic wrap on counters.
10) Inspect all ceilings and clean window frames while looking for water intrusion, black spots indicate moisture and possible mold.
11) Check and replace if necessary any water main shut off valves if not working.
12) Check and replace if necessary any pressure relief valves on water heaters.
13) Check and replace hot and cold hoses to washing machine. Any sign of yellowing indicates a leaking fixture.