Nordyne 3A fuse pop problem

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Old 12-23-16, 12:33 PM
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Nordyne 3A fuse pop problem

So I have a Nordyne FG6RC 100N - 16B furnace and the 3A fuse on the control board keep blowing. Recently a contractor replaced the transformer and supposedly the control board (but I did not see the old one). A month later the 3A fuse keep blowing-- it will blow at any time between 15minutes to 3 days after starting. I have checked for shorts (with a multimeter) between the terminal wires and there are none. The 3A fuse did not blow when I left just the fan on (no heat). Any idea where the problem could be and how to test for that.
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Moderators note: Moved to its own thread.
 

Last edited by PJmax; 12-24-16 at 04:18 PM.
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Old 12-23-16, 01:00 PM
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You said the fuse blew with all the thermostat wiring disconnected. That's telling me you have a short to ground in the safety stat lines. That would be the round two prong devices fastened to the metal plenum. When you unplug the 11 pin plug.... these safeties are disconnected from the board.
Did you do this? If so what was the results?
 
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Old 12-23-16, 03:32 PM
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saltydog463, that last post was from a different poster.

Jack201, is your fuse popping in cool mode or heat mode?
 
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Old 12-24-16, 02:49 PM
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Possibly the metal foil on the inside of the face of the heat exchanger is loose and fell across the limit switch. I have seen this happen. Remove the limit to check or remove wires from limit and jump them together for a test only.
 
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Old 12-24-16, 08:08 PM
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If your system has a humidifier you may find a short in it's low voltage wiring. It is not uncommon for installers to snake wires through sharp edged holes in the ducts that frays insulation. This kind of short can be very intermittent.
 
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