What to Do When Your HVAC System Won't Turn On

HVAC systems draw massive electrical loads. Locate your home’s main electrical panel. Look for double-pole breakers labeled AC, Furnace, or Air Handler. Firmly switch them completely to the OFF position, then back to the ON position to reset them.

If the thermostat screen is blank, change the batteries. Even hardwired thermostats sometimes rely on battery backups to close the relays that send the start signal.

Modern air conditioners have float switches installed in their condensation drain lines. If the drain backs up with algae, the float switch trips, completely cutting power to the thermostat to prevent water damage to your ceiling. Check your indoor unit's drain pan for standing water.