Nordyne / Frigidaire high limit sensor replacement?

[doublehorn]

OK all, I have a 2007 Frigidaire furnace that started throwing a 4 blink code, which indicates an open high limit switch according to the manual. So I pulled that switch, measured about 4 ohms of resistance at room temperature, so that all checks out so far. I ordered a new one from Nordyne, measured it at 0.6 ohms at room temp, which seemed plausible, but the controller board is still showing an open high limit code with the new switch and of course, no heat.

So the question is, do I need to reset that error code somehow on the controller board? I've disconnected the 120v power to that unit entirely several times, which I would have assumed resets the board.

Any suggestions? Could the controller board itself maybe be the problem?

 

[Fitter30]

Cycling power resets control. Need to ring out the circuit since limit wires might run to a limit on the heat exchanger inside the cabinet. Look at the wiring diagram follow the limit circuit starting with the control. Have problems take pic of wiring diagram and the control for the model number.

 

[Sponsor]

 

[doublehorn]

K, cool, thanks for that f30. I'll confess now to not being a furnace tech. I have some basic electronic and electrical diagnostic capacity, but I'm just Joe Homeowner. I'm going to have to educate myself a little bit about exactly how to test that circuit from end to end to find where it's open, which I think is what you're saying. The high limit switch does connect to a few other widgets inside the chassis whose function is unknown to me, but I'll take a closer look at the manual.

 

[Fitter30]

Take a pic of the wiring diagram usually on inside blower door and brand, model number of furnace.

 

[doublehorn]

OK f30, here's the placard on the inside of the door. Interestingly, the 4 blink code on this diagram indicates something different than the manual I found online. This diagram says 4 blinks = ignition failure, nothing to do with the high limit circuit. So I'm wondering now if this is just an air lock in the gas supply? do you suppose that's a reason we might get an ignition failure code? When I cycle the power, the pre-venting runs for a few seconds, then the ignition element lights for a few seconds until it gives up, so that all seems consistent with no gas supply being the problem.

Any thoughts?

 

[Fitter30]

Replace the igniter doesn't pull enough amperage board won 't open gas valve. Appliance part store should have a match bring the hot surface igniter with u might have to spice plug on. Do not touch the new one carbon with out gloves. Can't read the diagram printing to blurred. Control boards when looking for info might not be exact from the factory to generic. Terminals might be the same or might have more or less. Plugins could also be different.

 

[doublehorn]

Thanks for you all your input, f30. Turned out to be the regulator on the meter after all that. The utility sent a guy out at first who said everything was fine with their meter, but after bashing my head against non-existent furnace problems sufficiently to be satisfied that's not where the problem was, I called again. The second guy they sent out immediately identified the regulator problem, swapped it out and the furnace lit no problem after that.

 

[WorthFlorida]

Thanks for you all your input, f30. Turned out to be the regulator on the meter after all that. The utility sent a guy out at first who said everything was fine with their meter, but after bashing my head against non-existent furnace problems sufficiently to be satisfied that's not where the problem was, I called again. The second guy they sent out immediately identified the regulator problem, swapped it out and the furnace lit no problem after that.

Good find! Ignition failure sure doesn't indicate why.