If the outdoor fan stopped but the compressor still runs — switch off immediately, heat will destroy the compressor. If only the indoor fan stopped, air won't reach the room but the unit isn't in immediate danger.
See if any of these signs match your device — each one increases the likelihood of this fault.
These are the causes we encounter while repairing AC fan not spinning — ranked from most to least common.
Fan capacitor burnt out or weak
Fan motor completely burned
Bearings worn out — locking up rotation
Disconnected or broken motor wire
Control board PCB failed and isn't sending the signal
Object stuck in the fan blades (paper, twig, insect)
Any of the following = a danger signal — call now and don't try to fix it yourself.
On-site diagnosis, clear pricing before any work, and a documented 6-month warranty.