Main Blower shuts off but draft inducer continues to run

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Old 01-13-09, 10:12 AM
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Main Blower shuts off but draft inducer continues to run

I have a Trane XL90 furnace that is about 18 years old. The draft inducer fan comes on and ignition of the gas is successful. Then the main blower comes on. The furnace runs for about 90 seconds and then the main blower shuts off but the draft inducer fan continues to run. This lasts for about thirty seconds and then the main blower comes on again and runs for another 30 seconds. It is possible that the flame and draft inducer fan shut off when the main blower comes on for the second time. I am a 53 year old female with limited furnace knowledge. Can anyone tell me what might be the problem?
 
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Old 01-13-09, 11:20 AM
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Check the ignition module to see if there are any flashing lights which might be identifying the reason the burners are shutting off. And usually the reason for the particular flashing light combination is given somewhere on the furnace, sometimes on the cover for the fan compartment.

Do you have a multimeter caspable of measuring AC voltage and know how to use it?
 
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Old 01-13-09, 11:48 AM
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Originally Posted by SeattlePioneer View Post
Check the ignition module to see if there are any flashing lights which might be identifying the reason the burners are shutting off. And usually the reason for the particular flashing light combination is given somewhere on the furnace, sometimes on the cover for the fan compartment.

Do you have a multimeter caspable of measuring AC voltage and know how to use it?
I honestly don't know where the ignition module is but I didn't see any flashing lights and I couldn't find anyplace where it described the reason for the flashing lights (which I couldn't find anyway) And no I don't have a multimeter. Maybe this is too advanced for me. I was just trying to save myself a few bucks if it was something simple. The repairman can't come until tomorrow and it's supposed to get in the single digits tonight. It's still heating the house but I was just trying to be proactive.
 
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Old 01-13-09, 11:55 AM
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While it's unlikely that the furnace is staying on long enough to overheat, it might be worth checking to see that the filters aren't plugged with dust, that the cold air return isn't covered up and that most or all the warm air vents are open.
 
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Old 01-13-09, 12:12 PM
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Hey SP...correct me if I mistate anything here.

Pinkshoes...I had a similar problem. I don't know the exacts of your furnace, but all I had to do was slightly adjust the limit switch on my Trane rooftop furnace. What it was doing was the burner was coming on, the fan would start, but it would cool off the chamber and then the fan would shutoff, but the burner would continue. Then the fan would come on again, the burner would shutoff and the fan would run for a bit longer.

My furnace is about the same age, and again, don't know exactly how the limit works, but it was just old and needed to have the limits moved just a few degrees (dirty contacts maybe?). Still well within specs according to the Pro's here, and now it functions just the way it should.
Inducer on, burners on, fan on......burners off, fan off. (or something like that...lol)

You may not be able to make these adjustments yourself, but if its something like that, there should be no need to replace parts. I'd bet its something to do with the limit switch settings though, since everythings seems to be burning/running otherwise.
 
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Old 01-13-09, 12:17 PM
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You might want to ask your repairman if the furnace has blinking error code signals, and if so how you can see then, and where the list identifying where the codes is located.
 
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Old 01-13-09, 12:53 PM
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I replaced the furnace filter yesterday and that is when the trouble started. They don't make the size filter I need so I have to kind of cram the wrong size in. I did notice that the last guy that serviced my furnace had put electrical tape over the sensors? on the bottom door (I assume these detect if that cover is off?) I don't know if that could have anything to do with it. I will have him show me where the lights are and the list of what they mean for next time.
 
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Old 01-13-09, 01:34 PM
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He probably forgot to remove the tape which he put there for troubleshooting the furnace. Well, we can hope he forgot.
 
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Old 01-13-09, 02:56 PM
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Thanks for the info gunguy and seattle pioneer. This was my first time on this site and people are very helpful. Have a good life.
 
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