Nordyne FG7SC Short Cycling


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Old 12-26-12, 02:17 PM
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Nordyne FG7SC Short Cycling

My unit is about 6 months old and is short cycling. It will short cycle 10-20 times then randomly stay on and heat my house which is giving me big temp swings. I already cleaned the flame sensor, checked grounds, checked wiring to make sure everything is tight, new air filter, all ducts are open and not obstructed. The cycle begins, gas valve opens and furnace ignites, blue flames then shuts off and does this 2x followed by the blower kicking on blowing cold air. The blower runs for a couple mins then shuts off restarting the same cycle. What could this be? I'm stumped.
 
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Old 12-26-12, 04:51 PM
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Diagnostic lights for easy troubleshooting without
counting flashes: Dedicated light for flame signal
strength and 2 lights in combination to indicate all
other fault codes with easy to recognize states without
counting flashes

What error code is displayed?
 
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Old 12-27-12, 07:21 AM
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Green/Red lights remain lit and the yellow turns on when the flame is present and flashes once when the flame goes out. The sticker on the furnace door says the yellow flash indicates weak flame sensor signal but I don't think that tells much.
 
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Old 12-28-12, 06:40 AM
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I checked resistance on my limit switch and it remains closed throughout the cycling.
 
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Old 12-29-12, 05:03 AM
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The tech came and it turns out that my vent line built up a lot of condensation and the vent was not properly sloped towards the furnace to drain. The inducer was gurgling as it was struggling to push exhaust thru the vent and the pressure switch was tripping like crazy (clicking nonstop) therefore not letting the gas remain on during the cycle. He drained a half bucket full of water out of the line when he corrected the slope and now it works just fine. I figured the water sound was normal since it had been doing that since i've moved in 2 weeks ago.
 
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Old 12-29-12, 10:15 AM
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The sticker on the furnace door says the yellow flash indicates weak flame sensor signal
Are you confident that LED chart pointed to flame sensor?

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Did your tech measure flame rectification?

 
 

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