The air filter was totally gross and dirty
If the air filter in your heating or cooling system is dirty and polluted, it will not work the way it should.
The air filter should trap dirt, dust, and indoor air pollutants.
When the air filter is gross and dirty, indoor air particles end up in the system and that can cause disfigurement; Dust and dirt can cause furnace and a/c complications. It can cause complications with the evaporator foils and eventually lead to system breakdown. A plugged and dirty air filter can also lead to a fire. A few years ago, I was toiling as a volunteer firefighter and there was a call at 2:00 in the day. Everyone hurried to get dressed as suddenly as possible so we could contain the disfigurement. The fire was down the street from my favorite video game store and I knew the building really well. The older building had not been remodeled in a long time. The ductwork was aged and falling apart and the owner of the building was not taking care of the site, then he was running the heat to keep the plumbing from chilly up, however he wasn’t handling official service or having someone else do it for him. The gross and dirty air filter caused a fire and half of the building was lost. I’m sure that the shopper had insurance, but the building required a lot of construction in order to be viable again for use. It’s been about 10 years since the fire and the building is still in the same shape that it was and the lot is a disaster.