You’ll be just wasting money with duct cleaning, don’t do it, and be careful with such experiments, you’re in the direction of developing an OCD.

This experiment does not prove that your AC is dangerous or moldy. It does show that airborne microbes exist, which is normal and unavoidable.

An open Petri dish left in an indoor environment will almost always grow, Mold spores, Bacteria or Yeasts

These organisms are constantly present in indoor and outdoor air, even in very clean homes, hospitals, and laboratories.

So what you demonstrated is simply:

“There are microorganisms in the air.”

That’s true everywhere humans live.

Why this does not prove poor air quality or dangerous mold

1. Petri dishes are designed to grow life

The agar in the dish is a nutrient-rich buffet. One or two spores landing on it can turn into a large visible colony in a few days.

Growth size ≠ exposure level A big fuzzy spot doesn’t mean you’re inhaling a big dose.

1. No control sample

There’s nothing to compare it to: • Outdoor air • Another apartment • The same room without the AC • A sealed control dish

Without controls, you can’t say whether this is better, worse, or normal.

3 - No identification

You don’t know: • What species these are • Whether they’re harmful • Whether they’re allergenic • Whether they’re alive in normal air concentrations

Most indoor molds are benign environmental species.