Defective limit switch

[CygnusSailor]

Does anyone happen to know the furnace model used in the CF305SKP, or more specifically the part number of the limit switch in that furnace? I believe I have a defective limit switch. Considering the relatively inexpensive nature of these switches, I thought that I would try to replace it myself.

Thanks,

Gary Harkins

[2slick]

If you can access the furnace, it will have a tag on the outer case. I suppose you're referring to the "sail switch", which proves combustion air flow. It is pretty simple to test with VOM if you can access it. On our Surburban the sail switch is in series with the high temperature limit. I just replaced the control board in ours. PITA, as ours is under the kitchen cabinet!

[CygnusSailor]

Thanks for the response! I looked up "suburban sail switch vs suburban limit switch" and they are apparently two different items. Apparently the sail switch will only operate if the amount of air flow is adequate. The limit switch operates at the time the thermostat calls for heat which runs the blower and allows the sail switch to sense the amount of air flow. NOTE: that may be wrong, but that's my best understanding of the two switches.

Gary

[2slick]

Originally Posted by CygnusSailor

Thanks for the response! I looked up "suburban sail switch vs suburban limit switch" and they are apparently two different items. Apparently the sail switch will only operate if the amount of air flow is adequate. The limit switch operates at the time the thermostat calls for heat which runs the blower and allows the sail switch to sense the amount of air flow. NOTE: that may be wrong, but that's my best understanding of the two switches.

Gary

Don’t know why I confused what you said. The limit switch is the one that opens in high temperature situations. On ours, they are in series, so either will cause the same symptoms. IIRC, the fan will run like 15 seconds then shut down if the above switches do not complete the circuit.


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