Coleman Evcon D.E.S. 80 short cycle

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Old 04-02-13, 12:10 AM
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Coleman Evcon D.E.S. 80 short cycle

I have an intermittent Coleman Furnace problem that is getting worse and Winter doesn't seem to want to end. The model is 2865E656. 1999 mid-efficient. I get short cycles where the Inducer starts up, the HSI glows, gas valve opens, I get a flame that lasts only 4 seconds and gas valve closes and flame goes out. HSI then glows again, gas valve opens, flame for another 4 seconds, then out. This happens one more time then nothing but the Inducer running. I can get the sequence going again by turning the emergency switch off/on, but I have found better success by opening and closing the Blower Door Cover. At times the furnace works perfectly, other times I hear it miss firing up but work on the second or third attempt. Then there are times I feel a chill in the house and hear the inducer running and then I open/close the Blower Cover to get it running. From what I have read, most furnaces have a dirty Flame Sensor that causes this problem. On this furnace, it appears there isn't one. I'm not sure how it detects a flame and I'm sure they couldn't build one without this safety feature. There are two sensors, Limit and Fan, but I'm sure these are only for if either get too hot, they would shut down the system. Does anyone have experience with this model of furnace and could share some knowledge? In my internet search, it seems this Coleman model has this common problem. I have included some pictures.
http://imageshack.us/scaled/large/58...andes80hsi.jpg
http://imageshack.us/scaled/large/85...es80wiring.jpg
http://imageshack.us/scaled/large/57...s80furnace.jpg
Thanks, Ray
 
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Old 04-02-13, 01:47 AM
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Welcome to the forums.

Your HSI is also the flame sensor. It's called local sense.

The HSI gets a buildup of oxides on it from the burning gas components as well as the actual silicone oxide turns into a glass-like finish which prevents the sensor circuit from working properly.

Make sure the control box is correctly grounded. Check and re-tighten mounting screws.
Make sure burner is well grounded.
Clean burner tube in the area where the HSI lights the burner.
Make sure the HSI is actually in the flame when the burner is lit.

If all that is ok and you still have the problem....you'll need to replace the HSI.
 
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Old 04-05-13, 07:03 PM
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Red face Solved

Thanks PJmax.
I had thought the HSI might be used for this but then changed my mind thinking, the HSI gets so red hot when AC is applied, how would it not be sensing a flame.
It must be a resistance thing that is changed with temperature. This one measures 145 ohms when cold. Not sure if that is good or fair. I cleaned the element lightly with a thin file, making sure I didn't touch it with my fingers. I also moved it to the end of the bracket, using a washer to help hold it in place. The tip is more into the flame now. No movement available to get it fully into the flame. Grounding was okay. After three days of operation I haven't found the furnace running for a long period with only the Inducer running. No more cold mornings. I think it is solved. I will try to find an HSI, through the Summer, to have as a spare for next Winter. Thanks again.
 
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Old 04-05-13, 08:15 PM
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You're welcome

Just some clarifications for your info. The flame becomes part of the flame sensor circuit. The flame converts the applied AC voltage into DC. That DC is a current loop....which is how the unit knows the burner is lit.

So the flame sensor circuit is carried from the control box > HSI > flame > ground > thru ground back to control box. That's why HSI placement in flame as well as good grounding is important.
 
 

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