Furnace does not work on very cold mornings- blower comes on to soon


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Old 12-07-11, 10:25 AM
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Furnace does not work on very cold mornings- blower comes on to soon

Have a Frigidaire(Nordyne) Model FG6RA 120C-20C unit is 6 years old
Unit is installed in the attic in separate room surrounded by dry rock and insulated on outside. I live just north of Chicago Illinois.
Heat set at 57˚F during the night so it will not come on until 6:30am when set at 67˚F

Typical cycle Ė power to unit (red led constant on)
Updraft blower comes on and 25 seconds later
Igniter comes on and stays on for 25 seconds and then the
Gas comes on and the flames ignite fully (yellow led on and continuously blinking)for 25 seconds
then the Blower comes on

On really cold mornings in the low 20ís and the house temp drops to low 60s high 50s

Furnace starts it typical cycle updraft blower, igniter, gas comes on and the flames ignite fully but then the blower comes on early after the gas only being on for 10 seconds. The gas shuts off and the flames go out and the blower will continue on for about a minute or two before it shuts down and the cycle will start again and will continue to fail. The first time this occurred I turned off the thermostat and waited till later in the day and then turned the thermostat back on and the system came on. When this occurred a third time in late January I learned I can get the furnace to work right away if I turn off the thermostat and run up to the attic and shut of the power to the furnace and wait 15 minutes or longer. Then I turn the thermostat back on and run up to the attic and turn power back on to the furnace (which seems to reset it) and the cycle will start and be normal. It seems that it is best to just shut off the thermostat at night and then before I turn it on go up to the furnace shut it off by the switch run back down turn the thermostat on, can hear it click telling the furnace we need heat, as I run back up and turn the power onto the furnace. I did this routine all throughout February last winter and then the problem stopped in March when the temperatures were warmer. This problem occurs usually only in the morning. During the day when my thermostat turns the temp down around 9am it usually has no problem coming on around 4-5pm, but then again the house does not get as cold as it does during the night and the sun may warm the attic more. My furnace has worked fine all fall and now it happened again only twice in three weeks. With it being so intermittent I have been hesitant to call in a repair man, but I canít really go away for the holiday if my heat has a problem.

I did pull the panel to check on any diagnostic codes for the leds. A yellow continuous flash means low flame sensor. The house is new and I have another nordyne/tappin furnace (looks the same as the Frigidaire- I think nordyne just slaps different manufactures on the same product) in the basement for the 1st floor and it has had no problems. The yellow led flashes continuously on this unit also.

Any suggestions on what it could be.

Thanks
 
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Old 12-07-11, 12:33 PM
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You didn't say what, if any, diagnostic code is being signaled.


The most like explanation for these symptoms is that the furnace is overheating and shutting off on the limit switch.

When the limit switch opens it shuts off the burners. Often the fan circulating air around the house will be switched on to cool off the overheated furnace. When the furnace is cooled off, the cycle will begin again.

Also, it'sa common for such symptoms to occur in cold weather when the furnace is on long enough to have a chance to overheat.

So-

One check for any diagnostic codes, especially one indicating that the limit switch is opening.

Use an AC voltmeter to see if the limit switch is opening when the burners are shutting off when the thermostat is still calling for heat.

Try turning the thermostat way up to keep the furnace turned on and see if that causes the problem to occur after giving the furnace a chance to overheat.
 
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Old 12-07-11, 07:38 PM
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start by cleaning the flame sensor. (should be done once a year anyway). Otherwise follow SP's instructions.
 
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Old 12-08-11, 08:15 AM
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Since the yellow led continuous flash means low flame sensor I cleaned the flame sensor and now when the gas comes on the unit displays a solid yellow led. But don't know if this will solve the problem because it has been flashing all the time when the furnace is working properly (and the led on my other furnace was blinking also with no problems at all- I cleaned this too and now solid yellow led).

The unit is definitely not overheating. This problem only occurs when the furnace is off all night (for approx 9-10 hrs) and tries to comes on for the 1st time in the morning when furnace is stone cold and the temperatures are in the low 20's outside and pretty cold up in my attic. I have put a thermometer in the room where the furnace is to see what the temp is when the problem occurs.

I also have to watch for the red led code the next time this happens. Unfortunately we haven't had any really cold weather lately, but suppose to get some tonight and tomorrow night. Will have to let house drop down to high 50's.
 
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Old 12-08-11, 08:57 AM
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You can't rule out a furnace that is overheating based on your explanation. In fact, should the problem recur, it would be my #1 suspicion.

It doesn't matter how cold it is inside or outside the house. The furnace can still overheat quite easily for a variety of reasons.

So if the problem recurs, use a voltmeter to check and see if the limit switch is opening.
 
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Old 11-09-12, 08:25 AM
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Smile Your solution

I have the Frigidaire FG6RC 080-16B model furnace that coded with the yellow flashing light. I cleaned to flame sensor usung a scotch brite and that cured the flashing yellow. I also had problems with my funace chronically overheating and discovered I had to switch the wires for the high fan speed from A/C to heat seasonally. If you check inside the panel cover it has a wiring diagram and on my furnace the black wire is for the high fan speed, which is generally for the A/C, and the blue wire is for medium high, which is generally considered high enough fan speed for the furnace. If I do not swap these wires so the furnace fan is on high then the furnace ices up the filter when the A/C runs, or overheats when the furnace runs. Things that help prevent both issues are making sure every vent in your home is open, keep your filter changed, and I keep my fan on "run" to help keep the temperature balanced since every vent is open.
 
 

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