What to Have Ready
If possible, know whether the issue is heating or cooling, what the thermostat is set to, when the symptom started, whether the indoor blower or outdoor unit is operating, and whether any breaker, error code, water, or ice is involved.
Urgent Safety Conditions
Fire, smoke, a suspected gas leak, a carbon-monoxide alarm, or another immediate life-safety hazard requires the appropriate emergency service or utility rather than routine HVAC troubleshooting.