Check the thermostat and airflow
Confirm cooling mode, a reasonable setpoint, and whether air is moving from the vents. Check an accessible filter and make sure major supply and return openings are not blocked.
Look for a pattern
Is the system running continuously, cycling off quickly, blowing warm air, or producing weak airflow? The pattern helps distinguish a broad 'not cooling' complaint from a more specific symptom.
When to call for AC repair
Call when basic checks do not restore cooling, the system repeatedly trips a breaker, ice appears, abnormal noise or odors develop, or the problem keeps returning.
Safety note: If you smell gas, see smoke or fire, suspect carbon monoxide, or believe there is an immediate safety danger, leave the area as appropriate and contact the relevant emergency or utility service. Do not treat an active safety emergency as a routine HVAC appointment.