Furnace blower motor problem

[pipling]

I have a problem with my Rheem RGFE furnace blower motor at my cottage. When I first get there it starts up fine, but then it won't work again that weekend with the fault code 61 "Blower Fault". When the furnace goes through its start up sequence the fan turns well but doesn't quite get up to speed. After a few retries the furnace shuts off.

My HVAC tech came out and had a look. He couldn't get it working, surmising that it worked earlier because there is a "flat spot" in the motor and I was just lucky that it happened to be turned to a favourable position. A new blower is about $2100 which I found expensive. He agreed and recommended getting a new furnace for $4400 with a 10-year warranty.

I understand where he is coming from, but I'm not quite ready to give up on a furnace that is just off warranty due to an intermittent problem. Since then, every time we go up to the cottage the blower starts fine on the first attempt. I marked the fins on the fan so I know it is starting up okay in different positions, so that theory doesn't pan out.

It seems to me there is a capacitor in there and the motor only comes up to full speed when it is fully discharged. Does that make any sense to anybody? The user manual for that fault also suggests "The motor Power Factor Correction (PFC) choke is faulty and needs replacing". Could that be my problem? Need some help with diagnosis to put my HVAC tech on the right track.

Thanks in advance for your expert opinions.

[Admin]

Marking the fins won't help you because as soon as the motor stops no one knows where gravity will stop the fins in relation to a possible dead spot on the motor.

The tech should have been able to diagnose if it was a problem with the fan motor or the ECM module.  Chances are you only need to replace the ECM module which is the round piece on the end of the fan motor and that would save you from spending $2100 for a complete motor assembly.

Are you sure the power supply is good at the cottage?

Likely the thermistor is bad inside the ECM module and you can simply bypass it or buy a new one for $1.50, but you would need to solder it on.  You're not going to find too many HVAC technicians willing to do this. Your best to remove the complete motor and take it to an electric motor specialist.

Here's a video that will explain how to bypass the thermistor,

https://youtu.be/XfGHC1O9ryk

[pipling]

Thanks for the video Admin, very interesting. I like your willingness to do a bit of tinkering to fix things. My auto mechanic is the same way, he has saved me $1000s over time by making clever repairs instead of buying overpriced parts. Unfortunately I have not been fortunate that way with HVAC techs, how do you find those guys?

The power to the cottage is generally fine, however there was an incident in late summer which may be a factor. A branch came down and severed the silver neutral wire while leaving the main power wire intact. The resulting voltage instability fried my surge protector but the electronics in the cottage seemed to be okay. However I could see how this might have stressed the thermistor. Do you think this could explain why the motor runs fine when it has been left alone for a week?

[Admin]

I really can't think of any reason why it would decide to work after sitting.  Usually that happens when things overheat.  If the other tech confirmed it was a bad motor then we can rule out a possible control board problem.

I believe this thermistor is designed to protect against an in rush of current.  It would make sense that it's the problem given the power problems.  When it comes to thermistors and resistance you can run into all sorts of intermittent problems.

There is nothing to lose by cutting off the thermistor and twisting its leads together.  The irony is this thermistor is supposed to protect the other electronics in the motor but it always seems to be what fails first resulting in the need for a complete motor replacement.

If you were to leave the thermostat fan set to on, and the fan running continuously, would this Code 61 happen when the fan speeds changed during heating or cooling?  It may only happen when the motor stops and then tries to restart.