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Old 11-08-2006, 06:01 PM   #1
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Gas furnace runs 4-10 mins. then flames extinguish?


My first post. Great site. Very helpful in the past. THANKS!!
American Standard model # AUD080C936A1. 80,000 Btu induced draft natural gas furnace with HSI and White-Rodgers 50A50-405 IFC goes through proper sequence and ignites. Runs well for between 4 & 10 minutes, then the flames go out. It cycles and tries to restart but does not. I have 24+ volts at both ends of thermostat, at secondary of transformer and at TH &TR terminals entering the IFC. Gas valve coil reads 98.7 ohms. I left volt meter on valve operator (M & C) during cycle. Read steady 24+ volts while burners were on. When burner flames go out voltage drops out simultaneously. When it cycles and tries to restart but fails the voltage (24+) jumps in and out with the failed ignition attempts. What should I check next? Thanks in advance.


Last edited by The Apprentice; 11-08-2006 at 06:20 PM.
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Old 11-08-2006, 07:21 PM   #2
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Gas furnace runs 4-10 mins. then flames extinguish?


What's the flash code on the board?

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Old 11-08-2006, 08:06 PM   #3
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Gas furnace runs 4-10 mins. then flames extinguish?


I forgot to mention that the flash code flashes rapidly but never changes. The inside cover states that continuous flashing means system normal. I never get anything different. THANKS.
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Old 11-09-2006, 12:06 AM   #4
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Gas furnace runs 4-10 mins. then flames extinguish?


Hi The Apprentice

Judging by your post you know what questions we are probably going to ask. The first thing that I would reccomend is go to your ignition module, set your meter for 24 volts a/c, put your meter in the thermostat ports of the module. Monitor your voltage, if voltage stays when the flames drop out, move your leads to the gas valve and see if the voltage remains when the flame drops out. If so you have a bad gas valve. If voltage drops off at the ignition control you probably have a intermittent limit trip or a thermostat that needs the anticipator set. But by what you are describing I am betting on a bad gas valve running the milliamps up and causing it to bounce the thermostat anticipator. If you have any further questions one of us will try and help.

Good luck
Rusty
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Old 11-09-2006, 08:57 PM   #5
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Gas furnace runs 4-10 mins. then flames extinguish?


dumb question, is your blower motor running? draft fan?
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Old 11-14-2006, 01:45 PM   #6
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Gas furnace runs 4-10 mins. then flames extinguish?


Firstly, this is a friend's furnace-not mine, so I cannot get to it everyday. The update is that more often than not the furnace does not light at all. It goes through the proper sequence (draft inducer comes on, HSI glows hot, gas valve opens and gas makes 2-3 attempts to light and then cycles again). You can see the gas flames light but immediately go out. After a few attempts the squirrel cage blower comes on to clear the air/heat. Transformer checks out fine as does the thermostat. Thermostat has terminal screws so I have since jumped out the thermostat and have the exact same symptons. As originally stated it occasionally lights and runs but flames cut out after a few minutes and then it will not relight. When testing the gas valve operator with a VOM the 24+ volts come on when it is supposed to but drop out when the flame drops out. If forced to pick which happens first I would say that the burner flames go out a split second before the voltage drops out. (Could that just be VOM response time?) Again more often than not the burners do not light. Mild weather right now here in RI but the cold weather is coming real soon. My friend does not have a lot of $$$$ which is how I got involved. I refuse to throw parts at it but I think it is the IFC board. Is there a proven way to test the IFC? Thanks in advance for your help.
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Old 11-14-2006, 02:43 PM   #7
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Gas furnace runs 4-10 mins. then flames extinguish?


Hi The Apprentice

First look at the post's by me and mhenry48, try the things I have reccomended to him. Let us know the results and that will help both you and I save alot of time and you alot of money.

Good luck
Rusty

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