A Carrier furnace will provide many years of efficient, dependable home heating with a minimum of maintenance. Some furnace servicing requires a professional technician, but there are a few simple periodic maintenance tasks, such as replacing a control fuse, that a homeowner can perform to help keep the system working properly. When the normal setting of the thermostat fails to trigger the heating function, a failed fuse is usually the culprit, and replacing the fuse is an easy procedure to restore the furnace's normal operation.
Turn off the power supply to the furnace. There may be an electrical subpanel installed in the furnace room or vicinity, but the simple and effective shutoff will be to switch the breaker labeled for the furnace in the home's main electrical panel.
Open the control panel on the front of the furnace. Some models have a thumb latch that snaps to open the control panel door. Some older models require a fixed screw on the panel face be loosened to release the door.
Test the fuse panel for power. Place the electrode tips of a voltage-amperage tester at both ends of a fuse or at each terminal of the connecting wires, whichever is applicable, to verify that the power is not flowing to the fuse panel.
Inspect the fuse or fuses to determine which fuse has failed. There may be a number of fuses, depending on the furnace system. A thin metal bar, visible through a glass window on a screw fuse or viewed from the side on a plastic buss fuse, will be broken on a failed fuse.
Remove the failed fuse or fuses from the panel by unscrewing the fuse or pulling the fuse out of its socket, depending on the type.
Screw or push the new fuse or fuses into the panel at the appropriate location.
Replace or close the furnace fuse panel cover.
Restore power to the furnace at the main electrical panel.
Switch on the furnace at the thermostat to verify proper ignition and operation.