I am very conscientious about upkeep for my furnace and air conditioner.
I make sure to replace air filters every month, and I schedule professional maintenance every spring and fall.
Because of my diligence, I was surprised when I had some complaints with the performance of the cooling system last summer. I first noticed that a couple of rooms felt rather overheated. Lowering the thermostat setting just made the rest of the house way too cold. Once I started paying attention, I realized that the air conditioner was running a lot more frequently and for longer cycles than usual. There was definitely less air coming from the vents but a lot more dust and other debris. I detected a musty odor in the air. When I scheduled a repair, the HVAC technician took the air conditioner apart and checked for any buildup of debris that might block airflow. He found nothing worrisome. He then tested the operation of the ventilation system and found that the ductwork was leaking air. Small holes and cracks at the seams were allowing approximately 30% of the conditioned air to escape. That energy waste was causing a lot more work for the air conditioner and much more expensive monthly energy bills. These flaws were also drawing contaminants into the system and spreading them into our breathing air. The duct sealing process took around two hours and was far less invasive than I expected. The technician sealed off the supply and return vents before pumping highly pressurized air into the ducts. The air was laced with adhesive particles, and as it escaped through the various holes and cracks, the particles built up along the edges and formed a seal.