High energy bills
Ductless AC is known for its energy efficiency. If you see a sudden spike in your energy costs alarm bells should go off. This is a good initial indicator that something is off somewhere inside the unit.
Noises from inside
A grinding, scraping noise from inside your ductless AC unit is a bad sign. Ductless AC systems run relatively quiet, with a humming noise typical to fans and condensers. If you hear anything out of the ordinary, it could be a sign of worn internal parts breaking down.
Foul odor
At its heart, diagnosing AC problems is a sensory experience. If it’s not a sound, it’s a smell. Foul odors coming from the interior of the unit when the power is on denote a leak or mechanical failure.