AC Won't Turn On
Quick Answer
When your AC won't turn on at all, it's usually a power issue. Check your thermostat first (batteries, settings, display), then your circuit breakers, and finally the outdoor disconnect switch. About 60% of "no power" issues are solved by these simple checks.
Safe Checks You Can Do
- 1Check the thermostat - Is the display on? Replace batteries if needed. Ensure it's set to "cool" and below room temp.
- 2Check circuit breakers - Look for tripped breakers (middle position). Both indoor and outdoor units have separate breakers.
- 3Check the disconnect switch - The gray box near the outdoor unit has a switch or pull-out block. Make sure it's in the "on" position.
- 4Look for a safety switch - Some units have a float switch in the drain pan that shuts off the system when full.
Likely Causes
- Tripped circuit breaker
Power surges, storms, or overloading can trip breakers. Indoor and outdoor units have separate breakers.
- Thermostat issues
Dead batteries, incorrect settings, or a failed thermostat can prevent the system from starting.
- Blown fuse
The outdoor disconnect box often contains fuses that can blow during power surges.
- Failed capacitor
The capacitor starts the motors. A failed one prevents the unit from turning on. You may hear a humming sound.
- Safety switch triggered
Float switches, high-pressure switches, or other safety devices can shut down the system.
When to Call a Pro
- Breakers trip repeatedly after resetting
- You hear humming but the unit doesn't start
- There's a burning smell from the unit
- The thermostat and breakers check out fine
- The outdoor unit has visible damage or burned wires