Total loss of electrical power to a residential indoor air handler blower motor is typically caused by a blown low-voltage control fuse, a tripped circuit breaker, or a safety switch interruption. If the small 3-amp or 5-amp automotive-style blade fuse on the indoor furnace control board blows due to a low-voltage wiring short or power surge, it instantly cuts off all control power, stopping the relay from sending line voltage to the blower motor. Another common cause is a tripped safety float switch in the condensate drain pan, which shuts down system power to prevent water damage when a drain line clogs. Additionally, a tripped circuit breaker in your main electrical panel will cut high-voltage power. You can troubleshoot by checking the furnace fuse and clearing condensate lines. You can verify that power has been successfully restored when the blower motor runs normally.
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