| DUO THERM furnace limit switch [message #65081] |
Fri, 20 November 2009 16:29  |
vernonite
Messages: 5
Registered: June 2009
Location: United States
Karma:
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Junior Member |
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My Duo Therm furnace (1978) comes on and runs for about a minute and then flame stops, fan continues (forever) no more heat.
I removed the limit switch and tested it with thermometer prob taped to Therm-o-disc and blowing on it with a hair drier, it opens at about 209 degrees and closes at 179 degrees (specs say 200 off, 170 on, close enough).
When I tested the furnace with limit switch jumped it runs but gets very hot. When air from vents reached 160 degrees I got concerned and shut it down (what is normal temperature of vent air?).
The fan is working good, lots of air from the 3 vents. Why does it get so hot as to trip the limit switch? or does the limit switch open and close during normal heat cycle? If is does then I must have a control module problem as it never recycles unless I turn the thermostat off and on.
If the limit switch is only a safty feature then it seems I must be getting too much flame to cause the overheating. Is there some way to adjust the flame?
John Wolever
Camp Verde, AZ
928-567-3805
[Updated on: Fri, 20 November 2009 16:44] Report message to a moderator |
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