Cut two access panels--one in the main supply and one in the main return line near the furnace.
Attach a high-powered and specially-made vacuum system to these holes.
Seal all vents in the home then power up the vacuum to create negative pressure in the duct system.
Open each vent, one at a time to access its ductwork. Clean debris from all the ductwork back to the furnace using long hoses and air-powered tools. Then re-seal the vent. Repeat this process with every vent in the house.
Access and clean the blower and its motor, the cooling coil and combustion components.
Remove the vacuum and re-seal the holes created in Step 1.