Quote:
Originally Posted by javelin
After re-reading my last post I think “if” the on/off switch at the furnace was flaky with a high resistance contact closure the furnace side of the switch (including the Coleman Mac red lead contact )would have the 2vdc problem voltage, but the main coach 12vdc feed to the switch should still be 12vdc. A temporary jumper across the switch would prove the switch is or is not the problem long term.
Another thing to try: if the sail switch occasionally sticks in the “prove” blower is running position, (typically might happen after the furnace has shut down after a normal cycle); you could temporarily disconnect the sail switch (tape over the loose wire end so it does not touch anything else) and see if your trouble voltage situation ever re-appears. Just wondering if the control board drags the 12vdc line down to 2 vdc when the sail switch sticks closed and always passes 12vdc to the blower running sense port of the control board. The only issue with sail switch disconnect is the blower will start but you should never get to the flame ignition/heat stage and the blower will just shut off. Its only a temporary situation though. Just be careful disconnecting connectors....you do not want to break off a microswitch connection or you will be doing a lot more work and cost to repair.
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Thanks Javelin, no worries I'm gonna keep trying to debug, and will be sure to post what I find. The intermittent problem is frustrating, and somehow only seems to show up in the middle of the night or snow storm...
I'm pretty sure it isnt the Off/Reset switch, when I first looked on here for a solution, someone said it may be that switch.... the second time the failure occurred (the first time it reset as I was removing the panel). That was the first place I went, toggled the switch on and off a few times. I even unscrewed the panel to better see the diagnostic light, and check the wiring, I toggled the switch a few more times. If it was a faulty/dirty contact on the switch it certainly would have made good contact as I toggled it - especially if its easily fixed now with a light thump on the side.
I really wish it would fail now so I can debug it better with the knowledge that I have now.
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