I hope that those customers you have with breathing problems don't follow your advice too closely. You are doing them a disservice. Dirt in your ducts does not always stay there, depending on what the contaminants are. I bet you tell your customers not to worry about mold either- just to kill it with bleach. Educate yourself before opening your mouth- You may kill someone someday with your opinion.
You can adjust for seasons: During the summer, you can have the air conditioner stay off during the cooler morning hours and start cooling the house as everyone gets up and starts moving around. During the winter, you can have your heater stay off while you are away at work and turn on about a half hour or so before you get home so that you are coming home to a nice, warm house.
Indoor Coil -- The indoor coil is a heat transfer device. It absorbs the heat from the inside of the house and passes it on to the refrigerant and is pumped outside. Dust that builds up on the coil can hamper its ability to absorb heat. High heat transference coils use very thin metal. Airborne chemicals can cause corrosion which leads to leaks. The constant vibration of the compressor can also cause solder joints to weaken and leak. An indoor coil may operate for weeks with a tiny leak, and you may not notice the loss in performance right away. As soon as a leak is made known, it should be replaced or repaired immediately.
"Customer service was great, and the price was in-line with other places, and fast service. We had a whole replacement of the outside and inside. I would have liked to see a better install for the furnace and new thermostat - the new thermostat should have gone where the old one was, and even tho the new furnace was a tight fit, they didn't offer to come back and repair the case molding, or give me a discount on the damage done, and I believe they should have put a disconnect box on the outside of the home, to make it easier for any future repairs needed. Other than that, am very happy with the cooling and heating!"