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Old 11-03-2012, 08:38 PM   #1
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Detailed questions about furnace


Ok, I am puzzled. I began this DIY project on my Bryant 373lav because when a call for heat was placed, the the inducer motor would start and the igniter would glow but no propane would be released by the gas valve. A test of the gas valve revealed no voltage.

The manual states I need a new control board, fine, done.

New control board installed (this one has the led diagnostic feature.) led 3 slow, 3 fast then swapping over to 1 slow and 3 fast, Flame Rollout Switch. All sensors test good for ohms, circuits closed but no there is no voltage when the unit is plugged in. Further, the fan begins blowing and does not stop until the unit is unplugged (I understand the reason for this.)

I also jumped each and everyone of them but could not identify which might be bad. I also jumped all of them at the same time, still the led flashes.

I am just a DIY kind of guy, certainly not a pro but know my way around most stuff but this one is kicking my A$$.

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Old 11-03-2012, 09:13 PM   #2
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Detailed questions about furnace


Roll out switches and limits should be closed, not open.

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Old 11-03-2012, 09:15 PM   #3
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Above the burners there should be a limit control stamped L170F or similar and attached to the wire from it is a red diode transistor thingy which is a thermal fuse and rollout device. If it is open then the fan will run all the time as the board thinks the limit is open and furnace is overheated and needs cooling down.
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Old 11-03-2012, 09:25 PM   #4
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Sorry, I meant the thermal switches are closed, therefore no resistance with the ohm meter.

I understand the thermal fuse above the burners, it doesn't have a red reset button like many but I have tested it with the ohmmeter; it is good. I have put jumper leads on it, no change. I have bypassed it taping the two wires together, no change.

I have done this with each and every thermal fuse in the unit, no change.

Sorry if I was unclear with my initial post, perhaps this clarifies the situation.
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Old 11-03-2012, 09:30 PM   #5
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One of the pins in the white Molex plugs/wiring harnesses may be damaged/pushed back or not making proper male/female connection. You need to check all those connections on the board and in the harnesses etc. If it has that skinny flat 16 pin connector those are easily damaged and hopefully you did not get it reversed and jammed on 180 degrees out.
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Old 11-03-2012, 09:35 PM   #6
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I will check all of the low voltage connections now.
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Old 11-03-2012, 10:54 PM   #7
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Thanks Gentlemen,

You can move that one over into the win column and have a beer!

Just as yuri suggested, Molex not fully seated.

Poor rookie running around in circles no more.
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Old 11-04-2012, 09:29 AM   #8
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Glad to help.
Had to learn EVERYTHING the hard way, I did.
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Old 11-04-2012, 12:44 PM   #9
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Quote:
Originally Posted by yuri View Post
Glad to help.
Had to learn EVERYTHING the hard way, I did.
The internet wasn't around when we were first learning the trade. We had to attend the school of hard knocks.

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