Electric blowers are used to move air and increase air circulation in cars and HVAC -- or "heating, cooling and ventilation" -- systems. Because of the amount of current these blower motors use, they require relays to provide a safer means of control. Relays allow a small current device or circuit to control a larger circuit carrying a much larger current. A wiring diagram for the relay is needed to verify how the relay should be wired and how many pins need to be used.
Set the 12-volt battery on the work table. Look at the relay wiring diagram and locate the two solenoid pins. These two pins are part of the low voltage circuit that will be used to turn the blower on. The remaining two pins are part of the high voltage side of the relay.
Connect the positive terminal of the battery to the positive terminal of the blower motor. Connect the negative terminal of the blower motor to the first high voltage pin of the relay. Then connect the second high voltage pin of the relay to the negative terminal of the battery.
Connect a low voltage to the two solenoid pins and the fan will turn on.
