Odors Might Be Caused By A Failed Evaporator
There is nothing worse than having bad odors come out of your air vents when you turn on your heat or air conditioning. Obviously, you are going to want to fix these problems as quickly as possible. When you have odors in your HVAC and duct systems, they seem to permeate. That is, you can often smell them even when your air is not turned on.
Obviously, one of the biggest jobs of your HVAC system is to filter the air.