Coleman evcon furnace works/doesn't work??


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Old 10-11-14, 02:41 PM
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Coleman evcon furnace works/doesn't work??

Hi guys. I have a Coleman Evcon furnace, using LPG, that has an intermittent prob. It will work correctly, then go whacko. Not sure what actual normal operation is, having NEVER watched it, when furnace was operating properly, so i can only tell you what it does/doesn't do now. When i believe it's working properly, it will call for heat, circuit board clicks on, then combustion motor/centrifugal switch kicks on. Seconds later, ignitor starts glowing, when it gets yellow hot, transformer opens gas valve, and flame lights. Ignitor now starts cooling down. After flame heats plenum? hot enough, blower kicks on. At the same instance blower kicks on, gas valve closes, and flame goes out. If it is working right, in my mind, ignitor will glow again, while blower is still on, then gas valve opens again, and flame re-ignites. This sequence will continue to happen, until thermostat is satisfied. Blower will now run, until plenum cools down, and blower turns off. All this time, green LED is solid....no flashing. When it is NOT working properly, ignitor will NOT re-glow the second time, and flame will NOT re-ignite. It is at this time, that green LED light will start flashing. It is a ONE flash, every so many seconds. Info for alerts, states that this is an "IGNITION FAILURE". That's visually obvious, but i have run out of ideas. This is what i have done up to now: Replaced circuit control board/replaced flame sensor/cleaned ignitor with emery cloth/checked NC limit switches with VOM ( both closed ). Circuit schematic included. Any suggestions, would be appreciated
 
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Old 10-11-14, 06:53 PM
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After flame heats plenum? hot enough, blower kicks on. At the same instance blower kicks on, gas valve closes, and flame goes out.
It sounds like your furnace uses a fan/limit switch that is acting up. When the plenum heats up the fan switch closes and the blower starts. If the plenum overheats.... the same control turns off the burner until the plenum cools down.

I can't see enough detail in your schematic to help you further. I'll need a larger photo or a model number of your furnace.


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Old 10-11-14, 11:13 PM
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Model # is DGAT056BDD PJ. This is the best i could do with pics.
 
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Old 10-12-14, 10:12 AM
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Thanks for the better pictures. I am temporarily stuck as I'm still looking for a service manual for your unit. Just wanted to let you know I didn't forget you.
 
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Old 10-12-14, 06:58 PM
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Thanks PJ. I'd scan, and post manual, if my scanner wasn't also on the #$@$% blink Don't think it's the cause, but i ordered the top NC 180 degree limit switch. Only $10, so not much to lose.
 
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Old 10-12-14, 08:13 PM
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You don't have the same fan/limit control I previously posted so that's out of the picture. For some reason that model furnace seems to be plagued by strange intermittent problems but I can't seem to find out what they are.
 
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Old 10-13-14, 10:48 AM
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"For some reason that model furnace seems to be plagued by strange intermittent problems but I can't seem to find out what they are."

Unfortunately PJ, that makes two of us
 
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Old 10-14-14, 08:42 AM
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Found prob with scanner PJ, and scanned pertinent pages of "user manual." The "user manual" PDF is only 5mb's, but upload to site, has failed 3 times in a row? May be on my end, but really not sure?
 
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Old 10-14-14, 09:33 AM
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I've sent you a PM...................
 
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Old 10-14-14, 02:01 PM
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Read, and replied........................
 
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Old 11-05-14, 01:54 PM
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Hey PJ. I think i may have determined problem. I believe it's this relay. I found it online, and it's not much, but was thinking i may not really need it, as NO ac is installed, and furnace is only used for heat. Can you, or anyone for that matter, give me correct info for jumping the relay out, as i don't need it, if it's only used for switching from HEAT, to AC?
 
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Old 11-08-14, 03:16 PM
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Jumping out a relay

Tried getting an answer to this, in HVAC, to no avail. Maybe i should have tried here first

I have a bad/intermittent relay in my furnace. It is used to jump between HEATING/AC. I do not have, or will have, AC, so instead of replacing relay, i'd rather jump it out. If someone can tell me which wires to bundle, or remove, i'd appreciate it
 
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Old 11-08-14, 07:23 PM
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You'd have been better off in HVAC.

That relay does not jump from A/C to heat.... it controls some type of damper for fresh air.
A make and model of the furnace would be helpful.
 
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Old 11-09-14, 03:11 PM
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I did/do have info in HVAC PJ ( http://www.doityourself.com/forum/ga...esnt-work.html ) In fact YOU were the only one responding. I agree, it does control damper mtr., but i also believe it controls AC.
 
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Old 11-09-14, 04:21 PM
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Ok... since we have the other thread we'll continue there.
 
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Old 11-09-14, 05:08 PM
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I didn't realize the manual info you sent me belonged to this thread.

At the same instance blower kicks on, gas valve closes, and flame goes out.
That's what we have to address. That blend air control relay doesn't look like it has anything to do with your ignition problem. You're having an ignition failure issue.

1) You will need to monitor the draft inducer pressure switch to see if it opens.
2) You may need to attach a volt meter to your flame sensor rod and monitor its operation. You would need a meter with a microamp scale setting.

Is there a part number on the control board ?
 
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Old 11-09-14, 05:25 PM
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Threads merged.

.
 
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Old 11-09-14, 08:38 PM
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Ok, as long as we're straight now. I don't have a "pressure switch", i believe my "centrifugal switch"
, in bottom of "booster motor", is what this furnace uses, in place of "pressure switch"??
I have a new control board, and new flame sensor. Control board # 7956-319p

Can't attach info again, so i'll send it to you via email, if you re-pm me your address
 
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Old 11-09-14, 08:58 PM
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Same difference..... centrifugal switch. Your doesn't monitor the flue pressure.... it just makes sure the draft inducer is actually spinning.

your control board is giving you a one flash... that's telling us that ignition is failing.

You changed the flame sensor but it could still be a flame sensor issue. The flame sensor needs to actually sit right in the flame. It creates a rectified voltage path thru the flame to ground. If your burner or control board doesn't have a solid ground it can fail. Usually you put a microamp meter in line between the single wire and the rod itself.

A video on the testing... youtube/watch?v=a5u044OJBc4
 
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Old 11-09-14, 09:23 PM
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Ok PJ, sent parts manual break down to your email.......found email address in my pm's. I checked sensor, before, and after i replaced it, and it's in the flame. Will try to watch vid, if i can save it, because i have Hughesnet satellite internet, and it sucks for watching vids. I don't have a microamp meter, so if it's cheap, i can buy tomorrow, if not, that's probably out of the question.......can it be tested out of line? Maybe i can take it to a electrical shop, and have it tested, if it can be tested out of line?
 
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Old 11-20-14, 03:34 PM
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Ok PJ, i'm back in business. Took sometime, as i had to call a tech, but he couldn't find exact prob either. His BEST guess, was a new gas valve. He based that on the fact everything else worked good, but flame was erratic, and would go off flame sensor for a split second, and shut-down valve. So i ordered new valve, and new orifice for that model/valve. Dawned on me that same night, that i had a 160k btu hanging lpg heater, in garage, and thought, "maybe one of those burner orifices would work"? As it wasn't working at all now, i figured i had nothing to lose by trying it. So i removed one, and removed orifice from furnace, and replaced it with the one from garage heater. Before i tried it, i measured both orifices with a vernier caliper, and the one i put in, was .077. The one taken out, or the original, was .054. Didn't know at the time, but that valve calls for a .082 orifice. That's a WHOPPING .028 difference from the orifice that was in the valve.......WHY?? it was in there, i have no idea, and have no idea how it has worked for the 4 yrs. i've been here?? ( maybe it wasn't working that great, in past winters, but just didn't realize it then? ) Anyways, i started up furnace, with .077 orifice installed, and it worked like it actually new what it was doing. Nice steady light blue flame, no gas flame fluttering, with a few yellow tips at end, where it hits deflector. Did install new .082 orifice, when it came in, a few days later, but it did not keep a steady flame burn, like .077 did, so i again re-installed .077, and it has been working great since then. So, $520 later, a new control board/flame sensor/gas valve i don't need, and ME finding the problem, that i think either one of those "TECHS?" should have found, i now have my furnace back. Thanks for all your help PJ, and i hope my findings help someone else
 
 

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