Furnace blower won't come on

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  #1  
Old 12-16-07, 03:25 PM
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Unhappy Furnace blower won't come on

We have a very old (30+ years) Sears gas furnace that has been well maintained. The blower suddenly stopped functioning. The pilot light stays lit, the burner comes on and stay on for approx. a minute then just shuts off. The blower never comes on. I know it's ancient and probably inefficient, but replacing it is not an option right now.

I do not have central AC so am unable to turn to "fan only". Motor is not hot and the blower wheel moves freely.

The limit control is set on 180. There are 2 fan dials. One says "fan off" and goes from 80-120. The other says "diff" and has 20, 40, 60, 80. I turned the "fan off" dial and get a clicking sound but that's it.

Help? Please?
 
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  #2  
Old 12-16-07, 04:38 PM
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Fan Control

Some pictures of the fan control would be a big help. You can post them on photobucket.com (free) & provide a link here. Do you have a voltmeter & know how to use it?
 
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Old 12-16-07, 05:44 PM
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Okay, here's the photobucket link.

http://s40.photobucket.com/albums/e2...ndapics137.jpg

My husband has a voltmeter but is out of town on a deer hunting expedition. However, I can borrow one from my electrician brother!
 
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Old 12-16-07, 06:01 PM
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Wiring diagram

I could not read the markings on the terminals for the controls.

There is usually a wiring diagram on the door to the fan. If there is, start at the fan motor & trace the wire (usually low{red} or med. low speed {blue or yellow}) back to where it connects to the fan control. Look for any burned wires. Turn the power off to the furnace before messing with any wires.
 
  #5  
Old 12-16-07, 06:37 PM
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hmmm...coming up from the fan motor, there is only one wire connected - a white wire that goes to a silver box next to the pilot assembly. (There is also a yellow wire there but it is not connected to the motor.) From the silver box, 3 wires go into the limit/fan switch - brown to the limit switch, black and yellow to the fan switch.

Being fairly mechanically inclined (for a female!), it looks like the problem may be that the yellow wire is not connected to the motor. I'll have to get some help to move the motor out to where I can see where it might need to connect. It's a bit on the heavy side for me.

You've been quite helpful...thanks.
 
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Old 12-17-07, 02:54 AM
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Blower wiring

That white should be neutral but be careful. Some manufacturers use yellow as a neutral & others use it for a different speed on the fan motor. If brother can understand the wiring diagram, he should be able to determine what is going on. If that motor has a capacitor, that too could be the problem. As brother to bring his meter.
 
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Old 12-17-07, 07:18 AM
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Thanks for your help. It got to 23 degrees during the night but I stayed fairly warm with an oil filled electric heater in the bedroom. My brother is out of town for a few days but I think my hubby will be back to help out. He has a good friend in the HVAC business.
 
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Old 12-17-07, 12:36 PM
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This is what we know:

It was working according to whatever the fanswitch settings were.

Then it stopped working.

And the blower never comes on even though burner runs for 1 minute.

.....................

If blower were in working order, with a burner flame of 1 minute, the blower may not come on. But after 2 or 3 back to back retries of this, the blower should come on even if after that the flame went out, due to captured heat in the exchanger.

Have you even tried to see if the squirrel cage can be spun by hand, to see that it is not froze up (bearings out)? That would have been the first thing I would have checked if that was me.

Then IF it did, I'd move onto trying to find out if the blower motor was burned out or had a dead short.

Then I'd check or have the capacitor checked.

...............

Taking guess on your fan switch settings: I'd say you now have it set "off" at 100 degrees (pointer straight down). Then if you had diff. set at 20, I'm guessing fan "on" would be 120.
 
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Old 12-17-07, 04:08 PM
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I wasn't able to get help today...things at work didn't allow me any time at lunch today. So, I guess another cold night!

ecman51 - Yes, I did check to make sure the squirrel cage turns and it does turn freely.

You are correct on the fan switch settings.

The unit is old so there is not a wiring diagram. I've tried to find one online and have not had any luck.

Is there an easy way to tell if the capacitor is out or will it require special equipment?
 
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Old 12-17-07, 06:07 PM
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Do you hear any kind of hum at the blower motor when it should be going? If not I doubt it is the capacitor. And also doubt it if it is not bulged or leaking some oil. In the absense of a hum, I'd doubt trying to push start it will do any good either. But you could try (use like a pencil and spin in direction of rotation, which would be with the arrow stamped on housing, or in the directioon of the cupping of the vanes, as if they are scooping air) that after you hear the click (in a minute to two?).

Where is this click sound coming from? I think that might be key. From that fan switch? Do you have 120 voltage INcoming to the fan switch?

If this click occurs say within 1-2 minutes of firing up the cold furnace, and you DO have INcoming voltage to the fan switch, I'd then test to see if 120 volts is leaving that fanswitch going to the blower motor first, when you hear that click if it is in that 1-2 minute time frame. If it never does, you have found your problem right there.

And if voltage does go to the blower motor at that time, and if there is no hum, and no apparent capacitor damage, I'd test the blower motor for resistance and see if there is a dead short.

But let us know if voltage leaves the fan switch heading to the motor.

And don't touch capacitor terminals with your fingers due to stored voltage.

You can research on the web ways to test capacitors. One way is of connecting ohm test leads on capactor's 2 far terminals and watching spike and fall, and then reversing leads and doing that and watching spike and fall and if it does that, it is likely good. Some other way utilizes hooking upa lightbulb in series with the capacitor and using voltmeter also to see how many volts, and then you correspond your readings to that of the listed mfd. rating on this chart. Or just take it to motor shop and have them test for you. But like I said, I have this feeling this is not it.
 
  #11  
Old 12-17-07, 06:51 PM
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Wiring Diagram

This furnace was most likely made by Inter City Products. On Sears furnaces, on the data plate, there is usually the Sears number & also the manufacturer's number. If you can get the manufacturer's number & it is an ICP, I can probably get a wiring diagram.
 
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