An electric furnace sequencer turns the various heating elements inside a furnace on and off as needed. Turning all of the elements on at once every time the furnace engages can cause a surge large enough to trip the breaker or blow the fuse.
If the fuse for the electric circuit powering a furnace keeps blowing or the breaker in the electrical box keeps tripping, the electric sequencer may be at fault. Turning off the circuit to the furnace, or to the entire house if necessary to ensure safety, is the first step to testing the sequencer. Disconnecting the wires from the sequencer to the coil terminals and using an ohmmeter to measure the resistance in the coil should yield a figure near 20 ohms. If the ohmmeter reads zero or much higher than 20, it is time for a new electric furnace sequencer.
Labeling all the wires connected to the existing sequencer and noting their connecting points is important before taking the old unit out. This makes it much easier to connect the new unit, as its similarity in construction means that putting a mounting screw to hold the new sequencer in place and connecting the wires in the same arrangement as the old unit completes the replacement. Turning the power back on and watching an entire heating cycle verifies that the new sequencer is functioning properly.