[Possible cause] 1. Blown fuse or tripped circuit breaker. 2. Furnace power switch to OFF 3. Furnace blower compartment door or panel loose or not properly installed. [Corrective Action] Replace fuse or reset breaker. Turn switch to ON Replace door panel in proper position to engage safety interlock or door switch. [Symptoms] 
No Heat/No Cool/No Fan (common problems)