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I have a N8MPN075B12A1 as well. It stopped heating the apartment. Blower motor still works. 2 flashes saying pressure switch stuck closed. By-pass pressure sw and everything runs but the fails 4 flashes:limit sw stuck open. I have three others in the basement. Swapped blower motors, pressure sw and control boards with no fix. Any other suggestions?
So when you bypass the pressure switch the furnace does light and work fine or doesn't?
Furnace initiates the start sequence. "exhaust fan" starts, relays click no light off, smell of gas. No ignition. 30 seconds, 4 flashes appear indication problem with limit switch.
Find the red wires that go into the plug on the control board. Cut them about 6 " away from the control board plug so that you leave yourself enough room to reconnect them with wire nuts when we are done. Take the two red wires coming out of the plug and wire nut them together so that it forms a loop going out of the plug then right back into the plug.
Now unplug the yellow and orange wire going to the pressure switch and start up the furnace. once the inducer draft motor starts up hook/jump this yellow and orange wire together and keep it together the whole time. Tell me if the hot surface igniter glows this time.
Just to verify, my two red wires one comes in from the thermostat and my other red wire goes out of M2, to the blower motor.For my system, they wired the press sw with two blue wires.Connection diagram is 329530-101 rev a
Hummm, no that is not the diagram. I have for this furnace that diagram you have is for a n9 which is 90% furnace and that is a whole different ball game.
Weird. The placard model number n8mp075b12a1 yet the number diagram and placard on the door is 329530-101 rev a. It does give the correct connection diagram with what i am showing here. Would a couple of pictures help? If so where can I send them.
I have the diagram you gave me and it shows the two blue wires connecting the pressure switch, but this diagram shows a smart valve with 3 plugs in it and the pressure switch and limits all tie into the smart valve (gas valve) is this correct?
Also what type of vent pipe comes off the furnace PVC or metal
Correct, a valve model #SV9541. Three electrical connections to the valve, pressure sw is wiring is blue.
Ok chances are that is your problem. These smart valves are known for getting a mind of their own. The limits and the pressure switch tie into the biggest plug on the valve hold down on this plug and then start the furnace up and see if you can get it to make proper connection. These connections get weak and the valve will start doing all kinds of things. The sad part is the only fix is a new valve if it is indeed the problem.