Garage furnace issue.


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Old 11-26-21, 02:37 PM
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Talking Garage furnace issue.

Hereís the gist. 1990ís Armstrong down draft furnace. Currently in garage shop. New flame sensor, new old style limit switch. (It has the copper jumper wire on it) The kind with the spring coil control. Turn on heat, flame comes on, fan then shortly after. But, the fan comes on before the switch hits the point where the fan should kick on. Then after heating up a bit it starts clicking allot and the flame keeps shutting down and coming back on. Over and over. Note: The air coming in in probably pretty cold. Someone told me that could be a factor. Itís just a garage furnace a bypass would work unless itís dangerous. Iím wanting to put a timer control on it anyway.
 
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Old 11-26-21, 04:51 PM
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But, the fan comes on before the switch hits the point where the fan should kick on.
If the fan turns on then the fan switch is closing too soon. Perhaps you need a new fan switch or a fan switch with a different setting.
 
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Old 11-26-21, 05:56 PM
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I’m assuming the fan switch and limit switch are separate parts. The limit switch and flame sensor are new. Not to say they couldn’t be the issue. New doesn’t mean perfect.
 
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Old 11-26-21, 06:30 PM
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I’m assuming the fan switch and limit switch are separate parts.
I would assume the same thing. That is why I said you might need to replace the fan switch. There could also ba a fan switch relay. Please you post the model number of your furnace.
 
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Old 11-27-21, 11:15 AM
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I’m assuming the fan switch and limit switch are separate parts.
Why assume.... you're right there.
You said spring controlled..... that would be a fan/limit control.

From what you are describing that control is bad.
If you tried adjusting he settings and didn't hold the plate from turning.... it's probably damged.

If you can't tell if it's being actuated.... put a meter on the leads.
 
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Old 11-27-21, 11:23 AM
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This is the label. EG7A75DC10-13
 
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Old 11-27-21, 11:29 AM
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I’m only assuming it’s not the limit switch because it’s new. The flame sensor also is new. That doesn’t mean working of course. I did hold down the plate as I adjusted it. I saw that in a video. I’m a bit baffled why it’s fine at first then flakes out. Going to drop a meter on it next. thanks.
 
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Old 11-27-21, 12:31 PM
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Update to issue. The unit initially runs fine. The limit switch does what it’s supposed to. ( I had bumped the fan manual button on the switch) What happens is as if something is overheating. The unit ran good for like ten minutes. (Cold garage shop). Then clicked, shut the flame down and kept lighting it again. The limit switch is half way between the fan on and flame on marks the entire time. The filters are clean, the inlet flow is good. 1 10” run and a 8” run. It shouldn’t be that. What could overheat? I thoroughly cleaned all the burners. Took them all out and wire brushed all the rust off. They’re still very solid.
could the cheap thermostat I have be effecting it? It’s just a basic heat only model.
 
 

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