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Squires015 · 04-26-2020, 06:58 PM

My atwood is having an issue. Fired it up, it started just fine and ran for awhile. It reached temperature and cut off. As the temperature dropped, it never came back on. I looked and see the red LED flashing once every 3 seconds. I can toggle the reset rocker switch on the front of the furnace and it restarts fine. Every time it gets to temperature and cycles off, upon restart the blower doesn't start and the LED is blinking.

Old-Biscuit · 04-26-2020, 07:21 PM

Error code.....
LED flashing 1X every 3 seconds is 'Limit switch/Airflow problem'

Which should be because FAN isn't running

If 'sail switch' is staying closed after initial operation circuit board will not allow restart

Squires015 · 04-26-2020, 07:46 PM

So do you know what would cause the fan to not try and start again? It appears to cycle properly the first time. It reaches temp, the gas turns off and the fan runs another 10-15 seconds

Old-Biscuit · 04-26-2020, 07:50 PM

Sail Switch stuck closed or circuit board failing

Squires015 · 04-26-2020, 08:05 PM

So the sail switch closed from the first cycle basically indicating a false air flow?

Old-Biscuit · 04-26-2020, 08:48 PM

Circuit board does a 'diagnositic' test prior to start.
If DC is present on limit switch/sail switch circuit then circuit board will NOT allow furance to start

Sail switch is a micro switch with a paddle that is in the room air side. Fan starts and when sufficient airflow is established the paddle moves closing the sail switch.
That allows DC current to go to circuit board which then allows Circuit Board to send DC to gas valve and spark electrode for ignition.

If sail switch sticks closed the diagnostic test shows DC available for ignition w/o fan running...........not safe condtion.

OR circuit board 'blw' circuit is faulty. (blower circuit that sends DC to motor)

Opening/reclosing On/Off switch on frame stops all DC and then puts DC back on resetting the furnace.

So if sail switch paddle moves freely then suspect is the circuit board.

Using a voltmeter trace the DC circuits
DC should be at 'PWR' connection on board (from battery thru on/off switch to board
Then when the thermostat closes DC should be on BLUE wire at connector to board and on WHITE wire to Sail Switch
(DC on blue wire signals board to send DC to Motor via 'BLW' connection on board)
No DC on RED wire from board to motor then board is faulty

Squires015 · 04-26-2020, 09:12 PM

Ok lastly, if the sail switch is stuck, do you suspect the issue to still be there after a toggle of the off/reset?

Squires015 · 05-02-2020, 10:32 AM

So I think the blower is actually just not getting the signal. When I flip the furnace on switch, it's intermittent on whether the blower turns on or not.