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Old 02-22-2011, 12:27 PM   #1
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Gas furnace fan keeps running

I have a really old Weatherking gas furnace, and the fan runs all the time. Replaced thermostat (needed replacement anyway) but problem persists. Could only stop fan by switching off power. Then I looked inside control panel and found tucked away under panel a 3'x6" grey box, only id is White-Rogers, inside label label says limit control. Its too new to be OE, and there is a long slide switch that is labeled Automatic/Manual. The switch was in the center. Switched it to auto and now the fan seems to be working properly, so far. Question is, is there any good reason for the switch to be positioned as described, why wasn't this a problem before, and what is this switch called so I can find out more about its purpose?
Thanks in advance.


Last edited by mongo1; 02-22-2011 at 01:51 PM.
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Old 02-22-2011, 01:46 PM   #2
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A picture might help someone identify the part and related items.


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Old 02-22-2011, 02:54 PM   #3
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Thanks, Bob22, but I'd have to get one of my kids to do it.
I think the switch was the problem, and possibly vibration caused the switch to move into the "null" position. Now that its set to auto it seems to work ok.
If it is in fact a limit switch, when should it be set in the manual position? And does the manual setting cause the fan to run even when the thermostat was telling the fan to shut down?
Thanks again for your response.
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gas furnace , weatherking

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