A thorough visual inspection is the best way to verify the cleanliness of your heating and cooling systems. All portions of the system should be visibly clean - i.e., such that you cannot see any debris with the naked eye. Have the contractor show you the following areas in your system after the cleaning work to verify that the job was performed satisfactorily:

Did the contractor clean the entire heating and cooling system, including ductwork and all components?
 Yes   No

Is the heat exchanger surface visibly clean?
 Yes   No

Are both sides of the cooling coil visibly clean?
 Yes   No

If you point a flashlight into the cooling coil, does light shine through the other side? It should if the coil is clean.
Is the coil fins straight and evenly spaced (as opposed to being bent over and smashed together)?
Is the coil drain pan completely clean and draining properly?
 Yes   No

Are newly installed access doors attached with more than just duct tape (i.e., screws, rivets, mastic, etc.)?
With the system running, there should be no air leakage through access doors or covers. Is this the case?
 Yes   No

Is the return air plenum free of visible dust or debris?
Do filters fit properly and are they the desired efficiency?
Is the supply air plenum (directly downstream of the air handling unit) free of moisture stains and contaminants?
 Yes   No

Are the fan blades clean and free of oil and debris?
Is the fan compartment free of visible dust or debris?
 Yes   No

Are interior ductwork surfaces free of visible debris? (Select several sites at random in both the return and supply sides of the system)
 Yes   No

Is the fibreglass material in good condition (i.e., free of tears and abrasions; well adhered to underlying materials)?
 Yes   No

Have you air vents been firmly reattached to the walls, floors, and / or ceilings?
Are the air vents visibly clean?
 Yes   No

Does the system function properly after cleaning?
Is the system operating free of any new or unusual noises?
 Yes   No

If you answered "No" to any of the above questions, this may indicate a problem with the job. Speak to your contractor regarding these issues and ask him to make corrections to his work such that you can answer all questions "Yes."