Quote:
Originally Posted by skids
There is a "sail switch" that confirms that there is airflow out the exhaust. Never had an issue with it, so I wouldn't know if you could smell gas in event of it failing.
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There is a series of “events” that take place before the furnace will light. If the sail switch fails, it won’t open the gas valve or apply spark (click).
If memory is operating in a proper manner it goes something like this:
Thermostat is turned up and heat is asked for. At that point the control board starts the “wheels” in motion. There is two separate fans (squirrel cages) that spin. Voltage goes from the board to a “limit” switch making sure the plenum isn’t too hot. Then to the sail switch to make sure there is enough air flow. At that point, voltage returns to the board and the gas valve opens and the igniter sparks. If those conditions don’t exist the furnace shuts down.
In normal operation once the “set temp” is reached, the board shuts the gas valve and goes into “cool down” mode, running the fans long enough to cool off the plenum.
I’ve seen the OP’s condition a few times and a mud nest is about the only condition that will allow gas to flow and igniter to spark but no heat (flame).
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2012 Copper Canyon 273FWRET being towed by a 1994 Ford F350 CC,LB,Dually diesel.
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