Furnace Doesn't Always Start


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Old 11-17-11, 02:00 PM
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Furnace Doesn't Always Start

I have a Day and Night up draft natural gas forced air furnace. Model number 394JAW060095. Electronic ignition and a squirrel cage blower. I have no computer lights or anything like that. It's probably about 15- 20 years old. This is a intermittent problem. I can turn it on and it works great. It reaches the proper temperature set by the thermostat and shuts off. But when the temperature drops I can hear the thermostat click on but nothing happens. If I wait a while 15 to 40 minutes it will come on. We don't use the furnace a lot. Any ideas.
 
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Old 11-17-11, 04:09 PM
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Take the cover off the burner compartment of the furnace.

Turn the thermostat up and carefully observe the sequence of events that occur.

When the furnace fails to start, you need to determine the stage of the ifnition process the furnace is at.

I presume you have the Carrier three wire pilot intermittent pilot ignition system. You might, for example, find that the pilot light is lit but the main burner isn't turning on.
 
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Old 11-18-11, 02:58 AM
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Furnace Doesn't Always Start

The last couple of nights it has been working great. Go figure. But when is was acting up I turned the thermostat on and it clicked. I then went out to check the furnace and it was just dead nothing happened. No electronic ignition, no pilot lite, no burner. Its just like it was never turned on. So I came back inside and turned off the thermostat waited 15 minutes or so turned the thermostat and then it worked.
 
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Old 11-18-11, 10:44 AM
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You have to provide a more detailed description of the ignition sequence if you want some help.
 
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Old 11-18-11, 02:44 PM
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Furnace doesn't always start

I turn on the thermostat it clicks, electronic ignition starts, the pilot light is then lite it runs for a while, then the main burner is ignited and warms up to the proper temperature and starts.
 
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Old 11-18-11, 03:17 PM
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OK. You probably have a Carrier 3 wire pilot ignition control, with green red and white wires going to the pilot burner.

You have now observed the sequence of events that occur when the furnace lights normally. Now you need to check the furnace when it has failed to light and see where it stopped along this sequence.

For example, you might find the pilot lit but the main burner not starting. Or you might find the pilot sparking but not lighting.

Report back what you find.
 
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Old 11-20-11, 02:14 AM
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The furnace has acted up lately. But when it did I would turn the thermostat on I hear it click and that's is where the sequence of events ended. It didn't go any further than that. No electronic ignition, no polite fame lit, no burner lit. It was like there was not power at all to the furnace. But the last 3 or four days it has been running great. I am thinking there may be a intermittent power short some where.
 
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Old 11-20-11, 09:21 AM
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When it fails to start I'd check to see if the limit switch is sticking in the open position.

Where is the click noise coming from?
 
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Old 11-20-11, 10:10 AM
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Originally Posted by SeattlePioneer
OK. You probably have a Carrier 3 wire pilot ignition control, with green red and white wires going to the pilot burner.

You have now observed the sequence of events that occur when the furnace lights normally. Now you need to check the furnace when it has failed to light and see where it stopped along this sequence.

For example, you might find the pilot lit but the main burner not starting. Or you might find the pilot sparking but not lighting.

Report back what you find.
Yippeeee, i finally get to see you wrong.
3 wire flame switch wire colors.........white yellow green

LOL
 
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Old 11-20-11, 10:27 AM
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Heh, heh! Thank you for the lesson, Yoda.
 
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Old 11-20-11, 08:42 PM
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Furance Doesn't always staart

The clicking sound is the wall thermostat clicking on sorry about the confusion . I will have to check out the limit switch.
 
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Old 12-13-11, 12:48 AM
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Furance Doesn't always start

I replaced the limit switch. Well it seem to work for awhile until tonight. I turned the inside thermostat on and nothing happened like there was no power. I went out to the furnace and turned the wall switch witch controls the power to the furnace on and off twice. The furnace started up and ran normally. This normally happens when it get colder outside. It's hard to believe the wall switch is bad.
 
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Old 12-13-11, 07:05 AM
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If the limit switch opens, the fan circulating air around the house switches on and to the high speed. You can verify that by disconnecting one of the wires to the limit switch.

When the wall switch is first turned on, you should hear a "clunk" as a relay closes if there is power to the furnace.

If the limit switch is open, you wont hear that clunk and the fan will start instead.
 
 

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