[Spydey]

Happy new year everyone!

I have a really old Lennox furnace which was running great but tonight I heard a popping noise, like something electrical blowing type of noise from the furnace. Now the furnace blower won't turn on. I can hear the furnace light and flame burning but the blower won't run. I can hear a click and then humming every few minutes which sounds like electrical current passing through to a switch or relay trying to start the blower motor. Sound seems to be emanating from the motor area. It hums for several seconds then stops and just keeps cycling like that every several minutes. i just shut the furnace off for now at the emergency shut off switch. Is the motor shot? I don't think it has a capacitor since its a very old furnace but I will check tomorrow since its like 5am pacific time here in Vancouver, Canada.

 

[carmon]

it sre sonds like motor is done.... is it tight to move... if power to it and it dont run I suspect you need a new one.....

 

[Spydey]

it sre sonds like motor is done.... is it tight to move... if power to it and it dont run I suspect you need a new one.....

Thanks for the quick reply carmon. Yah I kinda have a feeling the motor is shot. I can hear power going to it by the humming noise I mentioned but it won't run. I haven't had a chance to actually go in and look at the motor and check if it spins freely. I will do that later on in the day. Thanks again for the advice.

 

[JJboy]

Check the capacitor first.

 

[how]

Of course it waits until it's -3F.
model or serial number will help.
A new humming sound with the motor not coming on is a likely motor/capaciter problem. Is it a direct drive motor or does it have a belt & pulley?

 

[how]

Of course it waits until it's -3F.
model or serial number will help.
A new humming sound with the motor not coming on is a likely motor/capaciter problem. Is it a direct drive motor or does it have a belt & pulley?
Continuing to run this furnace right now will be stressing a very old heatexchanger.

 

[how]

Spinning the cage only tells you it's a motor problem if the motor is seizing. Lot's of electrical motor failures still allow the motor to spin easily.
A Capaciter change is a cheap and easy part for a DIY to throw at it. Pick up the identical capaciter if you going to try that.
If you can't find the motor capaciter either you've got a shaded pole motor or perhaps you have a belt &pulley. Then I'd make sure you've got decent electral motor connections and 120V when the furnace is hot.
Don't play with anything unless you've cut off the power to the furnace first.

 

[Spydey]

Thanks for all the replies. I don't think there's a capacitor on the motor since it's a pretty old furnace. I would say the furnace is from the 70's. It's a belt and pulley style motor. I shut the power off already at the emergency shut off switch but I'll probably turn off power at the breaker also before I start troubleshooting. I still haven't gotten a chance to look at it yet as I was very busy today but I will check tomorrow and post back.

 

[Marty S.]

Those old belt drive Lennox furnaces had an access door on the back. Pull the screws out and look for thin cracks on the back of the exchanger before replacing a motor. Keep in mind that it's less than 70% AFUE so lots of gas being wasted. A new furnace will pay for itself over time.

 

[Spydey]

I finally had a chance to inspect my furnace and the motor was toast. I replaced it with a new Packard 1/4hp 115v motor. I now have heat but another problem has surfaced. The blower will not shut off and runs continuous unless I turn the emergency shut off switch to the off position. My thermostat seems fine and it doesn't have any manual or auto settings on it as its an old thermostat. Some weird things are happening when it's cycling. I can hear the burner shut off for like a few seconds then I hear this weird clicking noise like a wire shorting or something and then the burner fires up again. It keeps doing this every few minutes while the blower runs continuously. Is it possible that I have wired the blower wrong? It seems pretty simple since it only has 2 wires ( white and black ) and a ground( yellow/green wire). Could it be my fan limit switch thats toast?

I did a quick inspection on the heat exchanger and it seems ok. I don't have AC on the unit so there's never been any kind of moisture getting in the furnace.

Need some quick advice on this as I don't think this clicking and cycling constantly is doing any good to the furnace.

Here's a couple pics on the blower wiring.
The white wire is line 1 and black is line 2 they're numbered 1 for line 1 and 4 for line 2.

Regarding the ground, one end was attached to the bracket that the motor came with but it didn't fit my original set up so I had to remove the motor from its original bracket and attach it to my furnace bracket. My furnace bracket didn't have a hole to attach the ground so I just attached it to the cover plate where the wiring goes. Is that ok where it is?