Your Surfprep sander was designed to be energy efficient and draws less than 1 amp when turned on in idle mode. When you depress the paddle switch, the amperage reaches 1-2 amps. The moment the sander touches a surface to be sanded, amp draw increases upwards of 2 amps and should activate the vacuum. Various brands of auto on/off vacuums require a minimum of 2 amps to detect an attached sander signaling it to cycle on or off. If you continue sanding, with sanding pressure applied to a surface, the vacuum should continue operating.