Combustion Fan Runs Constantly

[wilson247]

Let me start out by saying I'm a maintenance technician at a manufacturing plant in Nashville, TN. While I do have a Universal license and have some formal training, I wouldn't dare lie to anyone and say that that I'm an HVAC Technician. I get by, but when it gets deep I call on my more qualified colleagues. Having said all that, here's my dilemma: While changing filters on 15 ton Trane Voyager package unit, I noticed that the combustion fan was running. I'm not sure what the exact temp was but it was somewhere in the 80's. I checked the t-stat and it was calling for cool not heat. My first reaction was to kill the disconnect and let it sit for a minute or so thinking that it might reset itself. As soon as the disconnect was turned on, the combustion fan came on. My next step was to swap out the ignition module/board with another unit of the same model. The combustion fan continued to run. Finally, I removed the fan assembly and installed in on another 15 ton Voyager, same model, that was operating properly. When I turned the disconnect on the combustion fan immediately came on. Needless to say, the problem is in the motor, I got that, but my little brain tells me that a motor doesn't do anything until its told to. One other thing I forgot to mention, this unit is just under 3 years old and this is the 2nd time this has happened. Fortunately this part is still under warranty and I intend on swapping it out tomorrow. Now, like I said I know what to do to correct this, but does anyone have any idea what could cause this? Is it just a fluke? Maybe the motor was assembled on Monday or Friday! Who knows, just thought I'd throw that out there. Any insight would be helpful.

[klrogers]

Its the motor, a common problem on these units.

Kevin

[troyorr]

Got any limits tripped or open? What does the schematic show in the fan circuit?

[Texas-Tech]

Trust me the motor is bad. We find them all the time

[ldmth44]

Seen same issue numerous times...it's the motor!

[otto]

it's the motor. you'll need an inducer assembly.

[johncavh]

agree you need a motor

[yorkamstd123]

its the motor just went through same prob

[highlifesipper]

What causes this?

[wilson247]

Yeah, there's no doubt that the motor is gone. This is the second time in 11 months. I'm just wondering what causes this. From what I'm hearing here and other places, it's a common problem. Just wondering if anyone knew what the root cause is. Thanks for all your responses.

[tlrutko312]

Motors do not just kick on unless they have voltage sent to them. Not sure what you guys are talking about but I'd be checking voltages before calling it a motor.

[Roncool]

Motors do not just kick on unless they have voltage sent to them. Not sure what you guys are talking about but I'd be checking voltages before calling it a motor.

Ya ME TOO I would first look for open limit

[johncavh]

this motor is feed voltage all the time

[otto]

It's a single phase motor with one leg constantly hot. The internal windings develop a shunt and this causes the motor to run continuously.

[ECIndHVAC]

LOL,

My uncle runs a supply house. He still tells the story, happened some 10 years ago, about a guy who changed out a blower motor because it ran all the time.

[Twilly]

Twilli says the thermostat.

[jimmit]

dont motters do what there told to do?????

[tlrutko312]

It's a single phase motor with one leg constantly hot. The internal windings develop a shunt and this causes the motor to run continuously.

Can I assume what you are saying is that the "shunt" you are referring to acts as a neutral?

[patrick]

Trane has put out a service bulliten about this. Like others have said it is the motor. I have replaced 3 myself. The last time when picking up the part at my local trane parts they asked me what the motor was doing, I told them and they gave me the part for free.

[kevink1955]

Motors do not just kick on unless they have voltage sent to them. Not sure what you guys are talking about but I'd be checking voltages before calling it a motor.

I do not know trane but on yorks the motor is 208 volt and only 1 line is switched, the other line goes to the line side of the compressor contactor. If the motor windings short to ground someware around the middle of the winding the motor will run on 115 volts. It may not get to full speed but it will run.