Limit Control Replacement procedure
To replace the control, begin by ensuring the power to the furnace is off. Then, on fan/limit type controls, mark the wires and write down there connecting points. (If the control is a fan/limit control, there will be four wires connected to it. Two of the wires are low voltage (24vac) and go to the limit switch. The other two wires are line voltage (120vac) and go to the fan switch.)
**NOTE** A simple limit switch will normally only have two wires and you cannot really hook it up wrong.
Then, remove the wires by pulling them off the connectors. Remove the two screws holding the control in place and remove the control from the furnace.
When performing a limit control replacement, it is very important to get the proper replacement. There are many different types and setpoints. The new control should match the old one in the following ways:
- The control should be the same style (snap disc, helical bimetal, fan/limit, etc.)
- The opening setpoint should be the same.
- The length of the sensing element should be the same.
After choosing the right replacement, mount the new control in the furnace. Then, reconnect the wires ensuring they are in the proper location.