you have a leak in your heater core which is attached to your radiator and heats the air inside your car interior
Filth in air ducts can cause many diseases and problems. Mold, mildew, and fungus can cause serious respiratory problems including Legionnaire's Disease. Bacterial growth can cause all kinds of illnesses. Rat droppings likewise. The unclean air ducts would more likely cause allergies and asthma than the common cold.
Dirty filter, dirty coil, closed damper, or duct has come loose from main trunk line. Rats will sometimes nest in air ducts and may chew holes through the ducts, especially the insulated plastic ducts. That's the worst case.
Hot water tank needs bleed of air,
Return ducts are under less pressure, but they need to move the same amount of air, so they must be larger.
My opinion would be to reroute the air ducts through the attic space. Saves time and money.
Ductless air conditioners are not better than ones with ducts. The reason why ductless air conditioners are not better than ones with ducts is that they don't remove the hot air as well.
You are able to still breathe because of the air ducts in the school. The air is cycled through these ducts, this renews the air in the classroom.
Any break or leak on the suction side of your pump can cause air in the lines.
Airflow improperly set (too high) or the most common undersized ducts.
One can clean the air ducts by getting a bucket with warm water and wiping down the ducts individually. However, please note it may not produce the same results as having them cleaned professionally.
It is possible to buy an air conditioning duct separately from an air conditioner. A great place to start looking is at www.ductworks.net/This site has a wide variety of air conditioner ducts.
So they dont get clogged up as this will stop air to pass through and humid air will build up as a result of this and therefore the dust in the air will cause irritation to lungs for asthma sufferers.