Listen and observe before resetting anything. Knowing whether the indoor blower and outdoor unit are running separates several fault paths.
Allow the normal compressor-protection delay
After a mode change or power restoration, many systems wait several minutes before starting the compressor. Do not repeatedly move the setpoint up and down.
If nothing runs
Check equipment power, service switches, and the filter. Some systems also have condensate safety switches that stop cooling when a drain problem raises water level.
If air moves but it is not cool
See whether the outdoor unit is operating. A tripped breaker can be reset once; if it trips again, leave the system off.
If you see ice, stop forcing cooling
Restricted airflow and other faults can freeze the evaporator. Turn off cooling and allow thawing according to the manual; do not chip ice from the coil.
Know the homeowner limit
Do not open electrical panels or handle refrigerant. An outdoor unit that will not start, hums, repeatedly trips protection, or a system that re-freezes needs qualified service.
“The thermostat is calling for cooling” does not prove the AC is delivering it; identify which stage failed to follow the call.
Sources
- ENERGY STAR — Heating and Cooling — Thermostat settings, filters, airflow, heating and cooling maintenance, and efficiency.
- U.S. Department of Energy — Air Conditioning — Air-conditioning efficiency, thermostat strategy, maintenance, and cooling-load reduction.