York Defrost Board Wiring Diagram

[Joseph]

Thelight-blue colored cluster of 5 resisters are rated 1 watt each but the 6th one at the lower right is higher than that, perhaps 5 watt. Just got too hot. Background heat may have been a factor also. Design should have provided for longer leads on those power resisters to put some space between them and the board. That's a fiberglass board, I believe.

last fall during a severe rain/thunderstorm with lightning i was walking by the furnace closet when the room lit up from a very nearby strike followed by a loud bang from the closet and the odor you'd expect from burnt electronics

Rheem/Ruud put their circuit boards inside metal enclosures in the blower compartment, which protects them pretty well from moisture and dirt. I suspect that it is, indeed, heat from the resistors, but it seems odd. I've looked at thousands of these things and never seen discoloration from resistors like this. I find myself wondering if this is a slow-moving failure in progress.

My hobby is old radios, so I've seen plenty of scorched parts. When a resistor gets hot, it usually is the result of a failure in another component that is being supplied by that resistor. So the fix there is not to just replace the scorched resistor, but to find the bad component that caused the scorch. And the modern repair for that is a new circuit board. ?

I have a Rheem Criterion furnace with what appears to be the exact same control board. Like yours, my board is burnt around the same resistors. Do you by chance know the part number or have a wiring diagram for that board?

As Rheem/Ruud serviceman since the 80's, I seriously doubt that resister is where the issue began. When they begin overheating, the middle lightens to a light brown color (towards the color of thoroughly combusted ash). It doesn't necessarily mean they're bad, they might be just overheated, damaged or simply very old.

The resister with the stripes does appear burned up. I haven't taken the board out to test it yet. The burners won't start. The igniter works but the automatic gas valve only gets 10 volts of power for maybe half a second. I figured the board was a likely candidate.

Yep, been there, done that. I made a point to get a whole photo to have before removing the wires. Once I remove the wires I should be able to find the part number information a lot easier. At that point I'll have a far better idea about the overall damage. Thanks for the help and information, I'll keep you posted.

On the back of the card it looks like a copper strip may have come off the board. My ohm meter can't track where the resistor goes on one leg and I see something suspicious looking on the board. This is also at the worst looking resistor, so if the board was damaged that's likely to be the spot. In the last image you can see an 'L' shaped piece on the board. It looks like a copper strip is missing there. I would love to see the front and back of a good board.

I noticed that the new card has a different layout for the wires. Are all the labels on the board pretty standard? I want to make sure I have a correct place for all those wires and plugs. I suppose I can compare the Amazon image with my board.

On my board there's a COM and 24VAC. The COM is the green and yellow wire plug, and the 24VAC is the yellow wire plug next to it. On the new board there is a COM and a SEC, both in a section designated as 24VAC XFMR. I'm assuming that the green and yellow wire plug goes to COM (just like the old board) and the yellow wire plug goes to SEC. Am I correct?

There are two control cables coming in. The small one with just two wires being used is from the outdoor section of your AC system. Heat pumps will use a third wire for the reversing valve. Not everyone uses the same colors on that cable. Just connect one to 'C' (common/neutral) and the other to yellow (Y) unless you have a heat pump. Those two-wire thermostat cables often don't have a yellow wire in them so folks choose something else, usually Blue.

Green (G) turns on the blower. Yellow (Y) turns on the AC compressor. White (W) turns on the heater. 'C' is the neutral connection for the 24 volt supply. The live wire that brings 24 volts to the thermostat seems to be the red wire on your card, which is common. These is the standard color code but I caution you to do two things before you turn the power on for the first time: Take the cover off of your thermostat and make sure the colors at each connections are the same on both thermostat and control card in the furnace. The other thing is to send me a clear photo so I can confirm as well as possible that it's correct.

I think all the small wires will be consistent because I'm just moving them from one board to the other board. I'm just going to make sure the colors are under the same letter screw. I'll definitely send you a photo first though.

The wires I'm asking about are the bigger yellow wires. On the old board the thick yellow wire has a thick green wire with it and it's connected to a screw labeled COM. Right next to that (also on the old board) is another thick yellow wire that connects to a screw labeled 24VAC. Those 2 wires are my primary focus. On the new card, the only remaining screws that appear to be the equivalent place to put those 2 wires are on a set of screws designated as 24VAC XFMR. In that section, one screw is labeled COM and the other one is labeled SEC.

It makes sense to me that the thick Yellow and Green from COM on old board will go to COM on new board and that the thick single Yellow wire from 24VAC on old board will go to SEC on new board. I'm just trying to clearly understand where their new homes are.

Something else to remember. On the card, if the 120 volt supply coming into the furnace from the receptacle is connected backward, everything will work fine but the ignition will try and always fail to ignite. The card knows if the neutral and 120 VAC connections are backward and will fail the ignition.

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