Short-jumping a furnace is a technique for starting the unit by bypassing the in-line thermostat, which is a different component from the wall thermostat typically used to adjust indoor temperature. Essentially a diagnostic technique, short-jumping allows you to determine whether the in-line thermostat is defective. This is not a permanent solution to a malfunctioning thermostat because the furnace blower motor will run continuously. Do not leave the furnace hot-wired this way without repairing any problem.
Things You'll Need
- Screwdriver set
- 18-gauge wire
- Wire strippers
Cut off the furnace at the circuit breaker or pull the fuse in a fuse box.
Take out the screws holding the cover on the side of the furnace to locate the in-line thermostat inside. The thermostat has a series of wires connected to the screw contacts.
Loosen the screws labeled L1 and L2 on the in-line thermostat.
Strip 1/2-inch of insulation from both ends of the 18-gauge wire using the wire strippers.
Wrap one end of the wire around the L1 screw and the other end around the L2 screw. Tighten the screws.
Remove your hands and all tools from the open furnace cabinet before switching on the circuit breaker or replacing the fuse. If the furnace blower motor activates immediately, you have a defective in-line thermostat that must be replaced for the furnace to operate efficiently.