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Now that the cold season is here i have been running the furnace. it is a Nordyne M3RL 90+ Downflow Condensing Furnace. The vent switch keeps popping on it, i have to reset the button alllll the time. when it pops it wont reset right away, you have to wait 5 minutes or so to let the vent tubing cool, then press it again. i checked all the tubes on the furnace for blockage/kinks, everything looks good. i checked the flue on the roof top to make sure air was blowing out, check good. i downloaded the owners manual and starting reading the description and troubleshooting and i think i have it narrowed down to either a weak vent switch, or my vent is too hot and therefore need to increase my blower speed. i looked all over the internet for some sort of schematic on the different configurations for the jumpers for the blower speeds. Below is the current configuration that my jumpers are in. My question is, what speed is my blower running with its current configuration? and what is the configuration for the other speeds this blower is capable of?

HUM
M1--Orange Wire
M2
M3--Blue Wire
HEAT--Red Wire

Russ,

There are several things it could be.......... But check this first as this has been a common problem with the M3.

Remove the inducer motor bell housing, its held in by 3 5/16" headed screws. You may have to loosen the pvc vent from the bell housing. In the back of the bell housing there should be a round disc about the size of a silver dollar with a small hole in the middle. This is the restrictor orifice. These have been melting to almost nothing, so you may only find some fragments. Miller/Nordyne has a newer style restrictor that has been trouble free.

If this is the case it will trip the vent safety switch as there is too much flame producing too
much heat.

Let us know how you make out.

Good Luck

Rod

Hi,

I would check the inducer orifice as Rod stated first to see if that is the problem.

Your red wire to HEAT terminal is correct for low speed.

Black wire to COOL for high speed.

White wire to NEUTRAL is the common wire for each.

Orange is medium low.

Blue is medium high.

M1, M2 and M3 are parking terminals for wires not being used.


Thanks,
Robert

Rod wrote:Remove the inducer motor bell housing, its held in by 3 5/16" headed screws.

is this inside the firebox? or behind the vent blower/motor?

Hi,

Read what Rod posted closely and if after doing so, you are still unsure what/how to go about this, then it is best to call in an hvac tech for proper diagnosis.


Thanks,
Robert

Just for your info, per Nordyne, the only units that were having this problem was the units manufactured in 2007, and only the 80000btu input. What I wonder is if the restrictor orifice hase also been decreased in size?? Does anyone know?? Tech support will not say..

The original poster did not state the BTU or Date of Manufacture.

We have seen this problem only on the 80K units.

We have had units that were manufactured in both 07 & 08 with this problem. Not so sure the size is different but the material its made out of is.

With these vent safety switches tripping we also noticed recently that the last few M3s we installed were 150 deg instead of 145.

Rod

Rod,
How can you find out the date of manf.?

Serial number.

Thanks,
Robert

What year was sku 903957---serial # m3a090200260 made?
Thanks,
Brian

Here is how Miller/Nordyne serial numbers read.

090200260

09= 2009.
02=February
260 = 260th unit built that month

Rod

Thanks Rod, I didn't have that info with me and went by what I found on the net. Not something I keep in my head these days. In looking at info again, I read it right, but got the month and year backwards, LOL.

Didn't pay any attention to model number at top of his post or it would have set off a light bulb that 2002 was too old a date.


Thanks,
Robert