[generalservices]

To mygirlsdad, Guess what? Remember the Nordyne furnace? Well it worked for a week and now it's blowing thr circuit board fuse (3 amp). We, 2 different hvac guys and me have it narrowed down to this. When we unhook the green ground wire that comes from the circuit board that goes to the furnace ground, the unit runs OK. But if the ground is hooked up it blows the fuse. With the power on there is 5 volts coming from that ground wire. One prob on the wire and one on the furnace body. If the thermostat calls for heat, that same ground wire coming from the circuit board will register 24volts between the wire and furnace body. A new circuit board and a 24volt transformer have been replaced and still the same thing. All wires have been checked, rechecked, unhooked, tried this and that and are at a loss. WE will be having a electronics tech coming Monday to look at it to see if he can figure anything out. Anyone has any ideas let me know.

[KC13]

Is the polarity of the transformer particular to the circuit board?

[generalservices]

KC13 I checked the polarity and all is in order.

[hvac1000]

Neutral and ground reversal problems. Is this furnace on a main electric panel or is it on a sub-panel off the main panel?

[generalservices]

I ran new 14-2 w/grd from the main 200 amp panel on a separate circuit. All polarity on 120 & 24 volt is correct.

[hvac1000]

Sounds good just be sure the neutral and ground are on the same grounding bar in the 200 amp main panel. With 5 volts present on the board ground wire to the furnace metal ground usually indicates a feed back problem with a low voltage device attached to the circuit board. Try disconnecting the thermostat and just use a jumper to activate the heat circuit and see if that eliminates the 5V feed back and fuse blowing problem. As mentioned before have you reversed the 24 volt secondary wires?

[generalservices]

I did reverse the 24v wires, no change and the grnd and nutural wire are on the same bar. I have used both a jumper and the thermostat. What is odd is that once I activate the heat circuit the 5v jumps to 24v on the grnd wire and at the same time the blower fan comes on. What I am going to do tomorrow is check out the fan motor and connections.

[KISS]

It might be time for the "light bub trick". Replace the fuse with two 12 V automotive bulbs in series drawing about 40 VA.

Now start unhooking things under fault conditions until the light goes out.

Don't forget things like the flame sensor.

[hvac1000]

The light bulb trick is a good one and disconnecting the motor might be worth a try. There has to be a back feed somewhere. Now if your unit has a variable speed blower motor that could also be a problem.

[generalservices]

Blower only one speed, but will ck it out w/ lite bulb in a.m. thanks

[hvac1000]

When you have time post the Exact model number. I have access to most factory service manuals and will post it for you if I can find it.

[generalservices]

Model is G6RC 080C-16B
Serial # G6A01080 7332

[hvac1000]

Parts list

http://www.transtaracsupply.com/pdf/g6ra_parts.pdf


Install

http://www.nordyne.com/Literature/708503a.pdf

[greghvacguy]

WOW.. I have seen this before. Found it to be 24volts reversed. Try and run a new ground wire from furnace to a copper pipe. Just a thought.Check all wires they mite be pinched some where.Look(pull out )main limit I have found foil on it from furnace cabnit.
Good luck let us know what you find we mite learn something here...

[greghvacguy]

Sorry Just one more thing is there a humidifer or air cleaner hooked up to the furnace if so diconect any wires that go to the furnace.There mite be a back feed from one of them.