Thor Forums

[Jevad]

Originally Posted by javelin

I thought about that too but normally the furnace motor starts first when the thermostat calls for heat and then the air flow from the blower is proven by the sail switch connecting 12v through the limit switch to the control board to continue the gas light process etc.

One other option is what if the sail switch remains stuck in the blower prove position sometimes.......maybe the 12v being applied to the control board through the prove circuit before it should be is causing the issue.....but there are no codes shown. Then banging the side of the coach frees the sail switch to return to normal open position. For such a new coach you would not think the sail switch would even be a problem....famous last words.

I think we may be on to something... I wish I could recall exactly the state of the Sail Switch when I was poking around in the furnace the other day when first trying to troubleshoot before I had the drawings. I did remove one wire, and thought it was closed.... (which could have been the issue) but I cant be positive.

I think I'll be a Atwood furnace expert by the time this is debugged, but thinking this through....

(Note the left detailed schematic and right side logical schematic in the manual are slightly conflicted, the left detailed side shows the power feed going from thermostat -> Sail switch, which when closed feeds the Limit switch. The RIGHT SIDE logical schematic, shows the thermostat feeding BOTH the Sail Switch AND the Limit switch. I will verify when I open up the panel the next time.)

The schematic shows the 12v feed from the power source ->
-> Off/Reset switch on the furnace then feeds the ->
-> Thermostat, which when temperature demand triggers then feeds back to ->
-> (depending on which schematic) The furnace Sail Switch and the Limit Switch OR Input on the Control Panel (I think is incorrect).

I see there is a relay on the Control Board that feeds the blower motor, so I suspect under the start condition input from the Thermostat, the controller board closes the blower relay, and watches the input for the Sail Switch to close. Once the control panel gets a signal that the fan is running (by the sail switch closure), it then ignites the furnace.

Now I wonder, if the Sail Switch is sticking CLOSED, what does the Ignition Control Board do? If the Control Board believes the fan should not be spinning and the Sail Fan should be open, does it prevent the Furnace from starting? Why does the voltage on the thermostat read only 2-3 volts? what is pulling that voltage down?

When it occurs again, I will definitely check voltages on each of the points of input... and see what I get. I will also check the state of the Sail Switch, open/close and see if I can trick it. If that doesnt work, I can try tapping the relay on the Control Board... to see if that resets it.

THANKS AGAIN!!!