How to tell if a blower motor fuse is blown?

Determining whether the low-voltage control fuse protecting your indoor air handler blower and thermostat circuit is blown involves a visual inspection and multimeter continuity testing. First, turn off the electrical power to your indoor HVAC unit at the main circuit breaker panel for safety, and remove the furnace service access panel. Locate the integrated electronic control board and find the small 3-amp or 5-amp automotive-style blade fuse plugged into it. Pull the fuse out of its socket and examine it closely under good lighting; if the internal metal wire loop is broken, melted, or blackened by electrical arcing, the fuse is blown. Alternatively, you can touch digital multimeter probes set to continuity across the fuse terminals. You can verify that the fuse is healthy when the multimeter beeps or shows zero ohms resistance.