1.) I'm looking to replace a faulty circuit board (#902696) in my Nordyne Miller GR5A furnace. Given that this model is pretty old, it looks like the replacement board is now replaced with ICM2805A.
Assuming that this board is in fact a suitable replacement, I've hit a point in connecting the new board in which the original board had 2 pins listed as 'UNUSED FAN' pins. My guess is that these fan pins are used in cases that the blower motor is a 4 speed vs a 3 speed, and those wires then are essentially useless. The 'UNUSED FAN' pins are simply a holding spot for the extra wiring. Is this assumption correct?
I'm not sure if the blower motor is a 3 or 4 speed, (GR5A-120C-16, part no. Can't find anything online on it)
2.) Comparing the wiring diagram of the original manual with the way it had been wired is not a match based on color. I'm curious as to why the original installer may have wired it this way, and if I should mirror the way it was wired on the new board or revert to the original wiring listed in the manual? See the diagrams below and their captions for more clarification. The first image is how the previous installer wired the motor, the second is what the manual calls for. The main difference here being the red and blue wiring. I've also included the mapping of wires to pins at the bottom of this post to help make the differences more concrete. Diagram of how the previous installer wired the blower motor. The main difference is the swapping of the red and blue wires. Red (and orange) are placed on the "UNUSUED FAN" pins, while Blue is on "HEAT". Diagram of how the manual specifies to wire the blower motor. Here the red wire is mapped to "HEAT", while the blue wire is placed onto the "UNUSED FAN" pin. Diagram of the original board with the "UNUSED FAN" pins.
Last edited by kkamin; 05-25-22 at 01:47 PM.
Reason: Determined that the new board has locations for blower pins, just need to verify in which way they should be wired.
The 'UNUSED FAN' pins are simply a holding spot for the extra wiring. Is this assumption correct?
Yes.... parking pins. Those wires are live without being connected.
I like pictures.
black - high
blue - medium
orange - medium low
red - low
white - neutral
If these are the colors coming from your motor then you have a four speed motor.
Black is typically used for A/C.
Blue or orange is typically used for heat. This color is selected by the amount of heat rise. Red is rarely used for heat. Don't go by any manual or schematic. Reconnect the heat color that was already used.
If you don't have any place for the spare two colors.... just tape the ends so they can't short out.
Hello, I have an oil burner that heats up the house in the winter and also the hot water. Now that we have the heat off we have been running into issue with the boiler not firing up to heat up the hot water. When I go down to check the boiler lights are all lit up. Usually a reset gets it going but I noticed when it fires on sometimes, something doesn't fully connect. It's been happening more and more frequently. Interesting enough this morning I turned the heat on and when I went to the boiler- it turned on immediately, stayed on, and I was able to get the hot water heater water warmed up. I quickly tuned the heat off (cause it's going to be in the 90s today) . I know I have to call for service but it's the weekend and it's just the hot water (I live in a two family with my mother in law so I can use her hot water if needed) I don't feel like paying extra for a emergency service call.
Anyways, why is this happening? just curious. I'm sure it's a bunch of reasons but I noticed we tend to run into this issue once we keep the heat off. The boiler was fine all winter- maybe needed to be restarted once or twice. I noticed that I have to restart it when the heat is off for a few hours when it starts getting warmer out. could just be a coincidence. I also know not to keep restarting the oil burner too.
I have a 25 year old gas heater. At the end of the heating cycle, instead of just stopping making all of its noises, with only the fan continuing for a minute or so blowing out the lingering heat, it's making what I can only describe as a winding down sound, like something is running slower and slower and then stopping, rather than just stopping. It's not loud, it's far too deep to be described as a whining, there's no banging or other noises associated with this, and there are no other visible problems at this time. I've used every synonym and phrase I can think of looking for articles about this sound, but no dice so far. Does anyone have any ideas?
05-25-22, 01:42 PM
