Why Is My Air Conditioner Not Turning On Despite Thermostat Set to Cool?

An air conditioner that won’t turn on with the thermostat set to Cool usually indicates a power, safety switch, or thermostat control problem. The most common real-world cause is incorrect thermostat settings or dead batteries, followed by a tripped breaker. Other frequent issues include a clogged condensate drain that trips a float switch, a frozen evaporator coil, low refrigerant from a leak, or electrical faults like a failed capacitor or loose low-voltage wiring. A tripped float switch from a backed-up drain line will quietly lock out cooling until the line is cleared. Our technicians handle these faults daily throughout the McKinney area.

Try these quick checks before calling:

• Set the thermostat to Cool, Fan Auto, and a temperature below the room reading; replace batteries.
• Reset the AC breaker and confirm the furnace/air handler switch is On.
• Replace a dirty filter; look for water in the drain pan.
• If you see ice, turn Cool Off and Fan On to thaw.

Turn the system off and call a pro if you see ice, water pooling, or smell burning.

Updated: 2026-06-03

Need help in Mckinney, TX? Call (214) 945-0660 or book online. "I highly recommend On Time Experts for any HVAC repair needs." — Kent R.