How to Wire a Limit Switch Control on a Honeywell Fan
The limit switch is a dual-purpose switch for a furnace that brings the fan on and off, and shuts the furnace down when it gets too hot, in order to avoid damage to the heat exchanger. One side of the switch brings the fan on at a set temperature to avoid blowing a cool draft. When the furnace goes off, the switch will hold the fan on to a lower set temperature to avoid overheating. The fan limit switch is mounted on the heat chamber and has a probe in back of it that goes through a hole in the heat chamber and senses the temperature. Does this Spark an idea?
Other People Are Reading
Instructions
-
-
1
Turn off the power to the furnace. Unscrew the screws on the access panel to get to the control panel. Pull the panel down and remove it. Locate the fan limit switch mounted on the heat chamber.
-
2
Remove the cover of the switch by sliding it off, and there will be a silver dial with three pointers on it. Adjusting the temperature setting is accomplished by moving the three pointers to the appropriate temperature setting. Notice in the bottom-left corner a white knob that is used to turn the fan on manually.
-
-
3
Looking at the switch, there are four holes with slots over them, an upper and lower on both the left and right sides. Slide the wires into these self-locking holes. Sticking a screwdriver into the slot above the hole releases the clamp for insertion.
-
4
Find the knock-out blank in the bottom of the fan limit switch and remove it with a pair of needle nose pliers. Pull the knock-out down and break it off with the pliers. Insert a stress bushing in the hole by pressing it in with your fingers. Pull the wires through the bushing. Wiring the switch can be accomplished in two different fashions -- three-wire installation or four-wire installation.
-
5
Push the line voltage wire into the left-bottom push-in terminal. Push the fan wire into the top left-side terminal. Push the third wire that operates the burners into the top-right terminal, and there is not a need to insert a wire into the lower-right terminal, given there is a jumper supplying power from the lower-left terminal.
-
6
Remove the jumper between the bottom terminals only for a four-wire hook up. Push the line voltage wire into the the lower-left terminal. Push a line voltage stem from the same wire into the bottom-right terminal. Push the fan wire into the top-left terminal and the wire from the high-voltage side of the transformer into the right-top terminal.
-
7
Set the pointers on the dial to the manufacture's recommended temperatures. Slide the cover back on, turn the electricity on and test the unit.
-
1
