Furnace Fan/Limit Switch


Old 09-21-00, 11:33 AM
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My blower fan runs continuously. I can get it to quit by rapping on the fan/limit switch. the switch has three settings-the highest (200 deg) I assume cuts the burner out. The middle one (140 deg) I assume switches the blower on. The lower one moves when I rotate the dial (is it to switch the blower off?) and sets itself at about 50 degrees. Or do the two upper switches do double duty and turn the blower and burner off AND on. Can someone explain this to me? I know, i could call the repairman, but I don't have anything better to do today, and I'd like to not pay for a new switch if i don't need one.
In gratitude,
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Old 09-21-00, 03:34 PM
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Based on the information you posted, it sounds like the fan switch is sticking in the closed postion.

This is a non repairable part. Therefore, you'll have to replace it.

Be sure to unplug the furnace first! The fan switch runs on full line voltage.

Make a hand drawing of the current locations of each wire connection.

Remove those connections, remove the switch, take it to the local appliance parts retail store and purchase an exact duplicate.

Reinstall the new one exactly as the prior one was installed. Then double check to be sure all wires are connected correctly.

Plug the furnace back into the electric outlet and cycle the heater on using the wall thermostat.

If the fan switch works, all was done correctly. Time to relax and have a BEER!

Good Luck,
Old 09-21-00, 10:08 PM
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That lower setting needs to stay in place, about 100 deg to shut off the blower. You said it is moving.

C A U T I O N !
Some of the replacement switchs have a jumper on the bottom between FAN and LIMIT.
If you have 4 wires to your old limit
2 for the FAN SWITCH
2 for the LIMIT
The JUMPER SHOULD BE REMOVED, brreak it out with a pair of neddle nose plyers.
Not removing the jumper could allow 120volts to cross over to the 24 volt side of the system.
Read the directions carefully.
Good luck.

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