Anyone with furnace repair knowledge for a odd issue I'm having?

GPGuy · February 25, 2016

I have had someone here a total of 4 times to fix this issue. My venter motor is making a mild humming noise that it didn't make before so as part of my furnace insurance thru the gas company they came out to replace the motor. As soon as they put the new one on it started to kick out the pilot light.

So they figured that there must be something wrong with the venter motor so they sent for a new one. When they came to fix it with the 2nd new one still the same issue.

So onto the pressure switch... which when the guy arrived to replace was the wrong one so he took a drive over to their parts warehouse and got the right one. Installed it and still the same issue.

Now in every instance as soon as they put in the old venter motor everything works perfect except for the humming. I'm not furnace expert although I have to admit that thru this ordeal I'm learning a lot...

Is there anyone here with knowledge in this area that might be able to come up with some kind of possibility, solution etc? Neither of the 2 guys that have been here seems to be able to come up with a resolution. His boss is supposed to call tomorrow... Will be interesting to see what he comes up with.

Any help or suggestion would be greatly appreciated.

GPGuy · February 25, 2016

Just in case it has more than one name the venter motor is the part that sends the air out the outside vent or chimney.

Colossus · February 26, 2016

Can you get a photo of it?

GPGuy · February 26, 2016

It's the round black part in the middle.

Brianibew · February 26, 2016

There is a pressure switch that ensures the draft inducer motor is working and producing an acceptable amount of pressue. I would make sure the motor that replaced the original motor is of the same RPM and if the squirrel cage was replaced as well, make sure they are the same size as the original. If the new fan/motor can't create enough pressure, it won't satisfy the pressure switch, and thus kill the pilot/gas valve.

Shawn5800 · February 26, 2016

Brian is correct ^^^. You could even have the tech re-install the new blower motor again, then bypass the switch (for troubleshooting purpose only) to prove that the pressure is not adequate for the system to say, "Ok, the pilot can stay lit."

Most times, its a simple switch that's either normally open or closed that you can bypass to "trick" the system.

Good luck.

sahls01gmc · February 26, 2016

Brian and Shawn are spot on. The new motors are probably not the same spec as yours.

Shawn5800 · February 26, 2016

I forgot to add, if the new motor ends up being very close to the same spec and the tech has sourced the closest possible match. Sometime there will be a POT or potentiometer that you can make an adjustment to either CC or clockwise to adjust the trip point of the sensor. Its typically a very small flathead set screw, typically sunken into the plastic housing so it does not get bumped.

I am not recommending that you do this to make up for insufficient airflow!

GPGuy · February 28, 2016

Thanks for the great replies! The info is very helpful as I don't have a lot of knowledge about furnaces. I think the probably may just be something to do with the part not be exactly to spec as the manufacturer of the furnace has gone out of business and this is a third party part. That being said I would think that someone else's furnace may have had some kinda problem too?

Is it possible to measure the RPM of this motor? The one guy told me this couldn't be measured and yet I'm pretty sure the first guy said differently?

Brianibew · February 28, 2016

It should be listed on the nameplate of the motor...if not, try googling the nameplate model number on the motor to see if you can find the specs. Also, make sure the squirrel cage is securely attached to the motor shaft and not slipping.