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

An air conditioner not turning on with the thermostat set to Cool usually means the system isn’t receiving the start signal or a safety device is holding it off. Most problems come from lost power, control setting errors, or a condensate overflow switch that stops cooling to prevent leaks. If the indoor blower runs but the outdoor unit is silent, a failed capacitor or contactor is a top suspect. In our Treasure Valley calls, we often find a tripped float switch after pollen or dust clogs the drain.

Check these quick items before scheduling service:

• Confirm the thermostat is on Cool with a setpoint below room temp; replace its batteries.
• Reset any tripped AC breaker and make sure the indoor unit’s service switch is on.
• Ensure the outdoor disconnect is fully seated and any nearby GFCI isn’t tripped.
• Replace a heavily clogged filter and clear a backed-up condensate drain; thaw ice before retrying.

If these steps don’t restore cooling, stop cycling power and book a professional diagnosis to prevent component damage.

Updated: 2026-06-18

Need help in Middleton, ID? Call (208) 378-6624 or book online.