9yo Armstrong fan turns on and off intermittently

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Old 02-18-11, 10:21 PM
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9yo Armstrong fan turns on and off intermittently

9 years old Armsrtong G1N80AV100D14B-1 couple days ago stopped working. Since it got warmer in Chicago didn't call for help immediately, trying to figure out myself whats wrong, but gave up. Tech guy came and charged me over $600 to replace gas valve/smart valve SV9510/SV9520. (from humidifier water was dripping and got into control board of the smart valve; don't ask me how, guy said it was a s***ty contractor/builder work and adviced me to keep water supply shut off)
He left and everything was good. Fan was on and ignition started, warm air came thru the vents....
An hour later. I noticed that the fan comes intermittently on for 2-6 sec on and then shuts off.
Than accidentaly walking by the thermostat (8 yo LUX 1500) I noticed that set temperature was lower then temperature of the room.
Thinking it is the thermostat sending wrong signal to borad to start the fan, I took off thermostat from the base (disconnected it). Well, guess what: fan is still intemittently coming on for 2-6 sec.

My suspiction is the control board, but need a second opinion.

I'm unemployed and that last tech visit drained me from any extra money I had.

Please, help.
 
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Old 02-18-11, 11:38 PM
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Start by taking the cover off the burner compartment of the furnace.

Turn the thermostat up (or connect the wires), and carefully observe the sequence of events that occur one after another.

Report that sequence here.
 
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Old 02-20-11, 01:59 PM
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When I got thermostat back to the base on the wall and turned it up so set temperature was higher then room temperature, the sequence was as it should be: the fan comes on, then igniter comes on, smart valve opens up, ignition, and after couple seconds blower comes up = warm air comes out of the vents.
So everything there is ok.

My problem is that between those times when room temperature comes below set temperature, repeat: between those times, fan comes on intermittently for 2-6 seconds then shuts off. Sometimes those startups comes in the series 2 or 3 ones after another. Usually breaks between those series are 10-30 seconds then it starts again....

Since it is a condo and the furnace is right in the kitchen/living-room space (behind a door), it is very unnerving.
 
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Old 02-20-11, 02:09 PM
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IF the thermostat is calling for heat the inducer motor should turn on and stay on until the thermostat is no longer calling for heat.

Erratic performance of the kind you describe might be due to a poor electrica connection someplace. When you experience that defect, I'd use an AC voltmeter connected between chassis ground and the W terminal of the furnace to see if the 24 VAC from the thermostat remains on.

I'd also measure the 120 VAC between the two wires of the inducer motor to verify that the inducer motor is shutting off because the power to it is being shut off by the ignition module.

Check for bad wiring from the W terminal to the ignition control too.

If it's not a bad wiring connection you can get to, it's probably a bad ignition control module you will need to replace.
 
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