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 points to a power issue, a safety shutdown, or a failed start component. The most common cause is a tripped breaker or a thermostat power problem. In many cases the system protects itself by shutting down when it senses water or electrical faults, and a stuck relay or weak capacitor can also stop it from starting. Around Peoria, we often see condensate float switches trip after heavy cooling cycles because the drain line is clogged before any breaker shows it.

• Replace thermostat batteries and confirm it’s set to Cool with the fan on Auto.
• Check the breaker and outdoor disconnect; if it trips again, stop.
• Look for water in the drain pan, which points to a tripped float switch.
• If the filter is packed, replace it and let any ice melt before retrying. $69 A/C Repair Diagnostic + Next Day Guarantee; Diagnostic Charge Waived With Service. If you smell burning, hear repeated clicking, or the breaker trips twice, turn the system off and call a pro.

Updated: 2026-06-19

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