Blower Fan Stays On

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  #1  
Old 03-30-05, 09:11 PM
Cooked_Electron
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Blower Fan Stays On

Hi...sure hope someone can help me.

Lately the blower on my furnace has been staying on for an abnormally long time...i.e. many hours straight. I thought it was an isolated incident a few days ago when it did this and then after a few hours the unit went back to normal. But it started again tonight.

My furnace is a gas Lennox G40UH (X) Series. And it's controlled by one of those Honeywell Programmable Thermostats.

The basic operations of the thermostat/furnace are working correctly. I get heat when I need it. The readouts look fine on the thermostat...it's just that blower keeps running and blowing cold air after the burners shut down.

I've tried turning the system "off" at the thermostat and nothing seems to happen...the blower keeps blowing. Of course it turns off when I shut the main power off to the furnace it self, but when I power up again it immediately kicks in and starts blowing.

I played around with the switches on the thermostat and they are set to "Auto" fan and "Heat".

The LED diagnostic lights on the furnace correspond to "Normal Operation or Blower On" according to the chart on the furnace.

I've been doin' some googling...alot acutally....and I've read somewhere that this model will do that if it's overheated and the "low limit switch" has been "switched" at some point due to any number of reasons. One of the reasons given was a dirty filter...I cleaned the filter...it's good.

Any input at all would be greatly appreciated. I hope it's something stupidly easy.

Thanks,

Chris
 
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  #2  
Old 03-31-05, 12:06 PM
Ed Imeduc's Avatar
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Wink

One of the reasons given was a dirty filter...I cleaned the filter...it's good.
Is this a washable filter that you have If so the AC coil cant have dirt in it.Sounds more like the fan relay there in the furnace. Its not up there in the tstat When the burner has been off for a time and the blower is on. Hit the side of the furnace with your hand hard and see it the blower will turn off if so its the fan relay. Look for it on the wire schematic of the furnace.

ED
 
  #3  
Old 03-31-05, 07:01 PM
Cooked_Electron
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You really want me to hit it? Cuz i'm 'bout ready to cave in the side of the furnace with a 10lb sledge hammer at this point. It's still blowing.

I've located the fan relay ... i think ... The wiring schematic on the furnace is pretty much greek to me. But it's the thing on the circuit board that clicks when the blower turns on right?

If it is in fact the fan relay...what do I have to do to fix it? Is the sledge hammer still an option? j/k

Thanks
 
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Old 04-01-05, 02:25 PM
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Wink

I dont know if you can replace it there or not if it pulls out then you can. if fixed to the board then its a new board. I did mean to hit the furnace with your hand . might tap on the relay there and it could stop the blower. but I get a new one

ED
 
  #5  
Old 04-05-05, 11:22 PM
Cooked_Electron
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Got it figured out!

Turns out my house has an "exhaust" fan located in the main bathroom that (i'm guessing) pulls a double duty of acting as a traditional bathroom fan and also it is supposed to help remove the stale air from the house. I guess it's a building code or something.

To help the process of removing the "old" air from the house it requires forced air from the furnace blower to aid in the evac of the old air. There are two switches that turn this exhaust fan on; one is near my tstat and the other is in the main bathroom. Each switch performs the same action and that is 1) turns on the exhaust fan. 2) simultaneously turns on the furnace blower.

There was a problem with the transformer in the junction box that connects the furnace blower to the exhaust fan switch. I'm assuming its function is to take the 120v switch to 24v for the furnace blower. One of the wires was loose in it. I reattached the wires in it and voila the blower turns on and off with the exhaust fan...and stays off now.

So yeah...that was the problem all along. Nothing technically "furnace related"

Thanks for the help anyways!
 
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Old 04-06-05, 05:09 AM
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Good find. I've not seen a setup like that yet.
 
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Old 04-06-05, 11:32 AM
LBC
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Those setups are common in new housing. Often times they are interlocked with the furnace via a vacuum switch on the suction side of the bathroom central exhaust fan. This switch then turns on the furnace blower to circulate more air throughout the house...
 
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