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Old 09-16-2020, 02:34 PM   #1
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Lennox Blower Motor Back and Forth but no full power


Hello,

I have a Lennox Signature Model G61MPV-36C-090-09 furnace. I was noticing that it was not heating the house when it started to get cold. I turned it on and off at the breaker and observed that it would ignite and blow flame but the blower fan would only rock back and forth, never reaching full speed.

I then turned the heat off and turned the fan only on. Same behaviour. It would rock back and forth, never accelerate up to a constant speed that would blow through the vents.

I have a video of it but cannot attach it here.

Thanks in advance!
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Old 09-16-2020, 02:47 PM   #2
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Re: Lennox Blower Motor Back and Forth but no full power


That is a older furnace ( over 15 years old ) and probably the motor itself is failing.

It rocks at start when it is charging the capacitors in the electronic module but whether it tells the motor to go to the correct speed depends on the main circuit board or the electronics in the motor module may be failing.

Ideally you should get a Lennox tech to check it as there are test procedures in the service manual for that.

Sit down and be prepared for a sticker shock as those motors are about $1000 and some of those furnaces have a obsolete main circuit board which is very expensive to replace.

If you have the Honeywell board you are OK but the White Rodgers is obsolete and replaced by the Honeywell with a conversion kit.

The motor module can be replaced on some but they are hard to get and not all techs want to replace them. Lennox likes to sell the complete motor and other brands do the same.
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Old 09-16-2020, 03:00 PM   #3
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Re: Lennox Blower Motor Back and Forth but no full power


Thanks Yuri,

It does have the Honeywell board. I was really hoping it was a capacitor problem like other models I read about but hope started failing when I couldn't locate the same type of capacitor on this one.
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Old 09-16-2020, 03:15 PM   #4
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Re: Lennox Blower Motor Back and Forth but no full power


There are ECM ( yours ) and PSC motors which have a external capacitor.

Yours has 3 big capacitors built into the module on the side of the motor with those 16 wire and other cables plugged into it.

PSC motors on have 4 fixed speeds and yours is variable speed.
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Old 09-17-2020, 01:04 PM   #5
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Re: Lennox Blower Motor Back and Forth but no full power


As a followup, I pulled the blower assembly and separated the motor from the ECM. I tested the motor leads and it looks like the motor itself is good (no shorted windings and the continuity is the same across all 3). That leaves the ECM itself.

I did a continuity test across the inrush current limiter and it shows 2.4 ohms so it's not burnt out so it must be somewhere else in the unit. Leaves me to conclude I need to replace the ECM (photo of the model is attached).
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Old 09-17-2020, 01:29 PM   #6
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Re: Lennox Blower Motor Back and Forth but no full power


There's a test procedure for the board and wiring harness -> https://yorkcentraltechtalk.wordpres...ooting-part-1/

I would not scrap that furnace if only the module is bad - see if you can buy a controller somewhere. it does have to be pre-programmed for your furnace model.
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Old 09-17-2020, 02:35 PM   #7
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Re: Lennox Blower Motor Back and Forth but no full power


I have checked the power to the motor from #5-3 and #5-4 and am getting 120 V.
I went and checked the low voltage harness based on what you sent and with Fan Only on I'm getting between 20-24V on all terminals except 2,4,7 and 9 which show no voltage and 15 which reads 45V.
With heat demand on, I get the same results but 2 now shows 45V.

My next question (after some searching) is what can I replace the ECM 2.3 with?
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Old 09-17-2020, 03:29 PM   #8
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Re: Lennox Blower Motor Back and Forth but no full power


Quote:
Originally Posted by CFernets View Post

My next question (after some searching) is what can I replace the ECM 2.3 with?
It's proprietary - for best results, you need the direct replacement motor and module or the module alone. The module must be programmed for your particular furnace too.

This is the downside of variable speed.

There is a universal replacement, likely not commonly available and for replacing ecm 2, would need to be installed with a programmer and manually tuned.

https://www.supplyhouse.com/Genteq-M...reen-VS-Motors

and

https://www.supplyhouse.com/Genteq-M...NEMA-48-CCW-CW

You must verify compatibility* before ordering and not take my word for it. *motor hp, etc.

Don't know if anyone here has experience with this product.

It doesn't look like an optimal solution for replacing older variable speed blower due to needing manual tuning and some functionality may be lost.
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Old 09-17-2020, 04:02 PM   #9
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Re: Lennox Blower Motor Back and Forth but no full power


Its the module that needs replaced not the motor.
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Old 09-17-2020, 08:58 PM   #10
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Re: Lennox Blower Motor Back and Forth but no full power


So if I find a unit like the one below, can I not replace the old one with this? Does a replacement unit have to be programmed for my specific furnace?
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Old 09-17-2020, 09:02 PM   #11
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Re: Lennox Blower Motor Back and Forth but no full power


Yes. Other wise it could move too much air, or not enough air.
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