Coleman lights up, but shuts down soon after...

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Coleman lights up, but shuts down soon after...

Postby justplumducky » Sat Nov 17, 2012 6:52 pm

Coleman Evcon Furnace
Model: DGAT07800
Serial Number: 970704823
Has Fresh Air Intake Duct coming from roof (attic?) that opens up (butterfly valve opens) when thermostat turns furnace on. One only On/Off switch (in a box) for this, just below blower assembly.

Furnace initially wouldn't light because ignitor had a bad spot in it (about 11 years old, I was told). Replace ignitor with new - now flame comes on (appears to be full, to me - have seen a weak one before), but shuts off soon after. Within about 10 seconds.

Is the flame sensor supposed to be directly in the path of the flame, almost immediately at the end of the main burner tube where the flame shoots out? Do these flame sensors ever fall out of position (rotate from vibration), so the sensor ends up pointing down, instead of horizontally (in front of the burner tube)? I can't be sure now, but I'm thinking maybe this flame sensor was, indeed, pointing downward. Going back tomorrow or Monday to take another look.

In the mean time, grateful for any help (other possible causes for this abrupt shut down situation?), if anyone hangs out here on a Sunday? (or tonight - Saturday night?). Have a safe weekend.
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Re: Coleman lights up, but shuts down soon after...

Postby justplumducky » Sat Nov 17, 2012 8:16 pm

Well, I just google'd for "Coleman main burner tube ignitor" and answered my own question about the position of the ignitor. Apparently, it is directly at the end of the main burner tube, in a horizontal position. Gotta go back & check this tomorrow.
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Re: Coleman lights up, but shuts down soon after...

Postby DaleM » Sun Nov 18, 2012 1:44 am

Coleman put out 2 different makes of furnace for a while, one with a seperate flame sensor and one without. The one without proves flame through the igniter. If you have the one with the seperate flame sensor you need to pull the burner and clean that sensor. Then looking at the burner there should be a small tang either at the bottom or side of the end of the burner tube. Be sure that is there and clean it. If it is gone/rusted away/ use a scuff pad to thoroughly clean the end of the burner tube assembly. The tang is/was there to provide a ground for the flame sensor to work correctly. Reassemble and test unit.
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Re: Coleman lights up, but shuts down soon after...

Postby justplumducky » Sun Nov 18, 2012 8:35 am

Thanks so much for your reply, Dale.

I did notice that tang and wondered what it was for... Now, I remember reading something about this... the path of current or voltage (for the flame sensor) actually goes through the flame (from the control board, via the flame sensor) to the burner tube (?), so if that's correct and that projecting tang (ground contact point) is gone, cleaning the end of the burner tube would be necessary to ensure a clean ground (contact point) at the end of the burner tube, in lieu of the tang (?)

Fast forward to later today. I went back today and cleaned the tang, but wasn't very dirty - minimal rust, but cleaned it up good. End of burner tube is clean. Flame sensor rod is directly in path of flame (at the circular edge/perimeter of burner tube). Flame sensor rod was not dirty or discolored hardly at all, but cleaned it up with a dry Brillo Pad - no help - still shuts down soon after flame lights up.

Green light on control board was flashing Once, pause, then repeat (legend for One Flash, said Ignition Failure).

Insulator on flame sensor isn't cracked or discolored. Electrical connection was tight, at the flame rod (the quick disconnect type). The other end of it went to a multi-pin connector plug on the control board - wasn't loose.

I have removed the flame sensor rod to take it with me to a supply house to get a price for a new one, but wondering if an ohms check on this sensor rod is a valid test for it, when it's removed/isolated from the control board circuit (it tests at zero ohms reading).

I discovered the microamps-dc test in an online article (Fieldpiece and elsewhere - the elsewhere may have been a copy of the the Fieldpiece article), but not sure where to connect the probes/alligator clips. I bought a Fieldpiece HS 35 which will do microamps-dc.
Last edited by justplumducky on Sun Nov 18, 2012 8:09 pm, edited 1 time in total.
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Re: Coleman lights up, but shuts down soon after...

Postby DaleM » Sun Nov 18, 2012 7:45 pm

How long does the flame burn? Does your furnace have a "trap door" or glass viewing port? It's located above the gas control valve.
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Re: Coleman lights up, but shuts down soon after...

Postby justplumducky » Sun Nov 18, 2012 8:04 pm

No trap door - glass viewing port. Flame stays on for only about 5 seconds or so.
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Re: Coleman lights up, but shuts down soon after...

Postby justplumducky » Sun Nov 18, 2012 9:01 pm

No trap door - glass viewing port. Flame stays on for only about 5 seconds or so.

Image

If this is how (the above pic) a multimeter should be hooked up, in series, to the flame sensor, I could do this.

In this pic, the white wire is coming from the control board and hooked up to the meter's black lead, and the meter red lead is hooked up directly to the quick disconnect on the flame sensor itself. Correct?

I would have to cut the the wire after it comes out of the control board box (headed to the flame sensor rod) and strip the ends, then use alligator clips connected to my multimeter to put the meter in series with the wire and get a uA's-dc reading, then wire nut the wire back together. I can use ceramic wire nuts if needed (higher heat capability). This sound workable?

The article says the mulitmeter should be capable of reading 1 to 10 microamps-dc. Any reading 1 to 10 uA's-dc is ok?

Or maybe you have a different suggestion altogether. Thx for your help.
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Re: Coleman lights up, but shuts down soon after...

Postby DaleM » Mon Nov 19, 2012 5:11 pm

Can you post a picture of your control module? Is it a board in a black or gray box, where you cannot see the circuit board or is it an exposed board housed in an enclosed metal control panel? The reason I ask is because we had problems with that furnace when it came out years ago. The flame sensors wouldn't sense flame correctly. The MFR sent out upgrades, a new box/board and burner assembly, that did NOT have the remote sensor. The upgrade proved flame through the igniter. The problem you will have testing is that trying to read the correct microamps when no flame is burning will be impossible, considering the burner only runs about 5 seconds.
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Re: Coleman lights up, but shuts down soon after...

Postby justplumducky » Mon Nov 19, 2012 8:46 pm

Currently, I have no way to get a pic from my phone to my PC. Digicam died - haven't replaced it yet. However... google'd for mobile home furnace pics, and this one from your own site is an exact match, including the Fresh Air box ("B"). Control board is in box A, mounted in a horizontal position (exposed), just off the surface of the horizontal partition that is supporting box A.

I may have mentioned it in my first post, but I had to replace this Hot Surface Ignitor with a new one - it had a hairline crack-type hot spot in it. Furnace was working fine, then cycled off, but wouldn't restart. I replace the HSI and immediately (first try), flame would not stay on (dropped in about 5 secs.). Been repeating this drop-off ever since. Didn't notice any obvious problems on control board (at least on its top-side).

Image

I took the flame sensor in to a supply house and talked with a former tech at the counter and he said there was no reason to install a new one. Ceramic insulator was not cracked or discolored, continuity check end-to-end was close to zero ohms, it was not shorted from the rod itself to its mounting bracket. The sensing portion of the rod (that gets hit with the flame) was very clean before and after I used steel wool on it.

Reinstalled the flame sensor and separated the sensor's quick disconnect in the wire on the outside of the burner ass'y, just above the gas valve, then inserted my probes into the q-disconnects and turned furnace on. Flame came on and initial reading was above 1 uA-dc (it may have been climbing to a higher number - I think it was at 1.9 just before it dropped off, but then immediately dropped down below 1 uA (before flame clicked off). It's still dropping the flame at close to 5 seconds (I timed it).

In box A, there is also a green ground wire that attached to one screw of the fan switch (or overheat switch) mounting flange/ear. This connection was good, and this ground wire lead back to a multi-pin connector on the left side of this control board. I removed the connector, as I did other various connections to make sure their contact was clean and tight.

I cleaned up the tang at the end of burner tube (wasn't very dirty) and the end of the burner tube itself was very clean. Looking thru the round sight glass, flame is full and hitting the sensor ok.

I bypassed the 4-wire (split system, central air), round Honeywell thermostat by jumping the red wire (after removing it from its terminal on t-stat) to the white wire (after removing it from its terminal), but was no help - same results. After 3 failed attempts today (and multiple other attempts Sunday), it still flashes the green light Once (Ignition Failure), pauses, then one flash again and repeats.

Very grateful for your help...
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Re: Coleman lights up, but shuts down soon after...

Postby justplumducky » Wed Nov 21, 2012 3:03 pm

Hi Cherrie - Welcome, and good luck on the website.
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Re: Coleman lights up, but shuts down soon after...

Postby justplumducky » Fri Nov 30, 2012 11:51 am

Turns out that this furnace was on an ongoing recall list for a possible overheat condition of the heat ex-changer, leading to property damage or worse. Here's the affected furnace models and website for more information:

The Coleman®, Coleman® Evcon, and Red T furnaces are used in manufactured housing. On these furnaces the name plate is found mounted on the left inside surface behind the lower panel. The furnaces are a silver color with white access panels.
DGAT070BDD
DGAT070BDE
DGAT070BDF
DGAT075BDD
DGAT075BDE
DGAT075BDF
DGAM075BDD
DGAM075BDE
DGAM075BDF
DLAS075BDD
DLAS075BDE
DLAS075BDF

These model numbers, and additional information, are found at this website address: http://dgatprogram.com .

The Recall Program Support Center: (888) 665-4640.
__________________________________________________________________

Contractor came out to handle the Recall service.

This pic is not the actual furnace, but is a match.
Image

First thing he did was to attempt starting the furnace. After he watched it shut down a few times, he checked manifold pressure - was 3.6 (spec on the gas valve was 3.5, natural gas). He checked flame sensor and agreed it was good. After finding no other obvious problems, he went ahead with the heat ex-changer replacement and said he would check the shutting down problem some more after finishing the recall work.

I watched the entire removal/replacement process, and there was no blockage around the baffle in the upper part of the heat ex-changer, nor in the stack above it going to the roof jack. After completing the replacement, he turns the furnace on and it was like it never had a problem to begin with!

When this contractor was attempting to start the furnace, before beginning the recall work, it was acting differently than it had been with my attempts, which were flame on, then shut down 5 seconds later. When he did it, the flame was coming on, but so was the blower, almost immediately. The flame would shut off in about 5 seconds, but the blower would keep on running. It was different with him, because he had the Fresh Air switch On, and my attempts were with that switch turned Off. During my initial attempts on my first day out there, I also tried it with the Fresh Air switch On, and got the same results as the contractor did, but all my subsequent attempts were with that switch turned Off.

For other non-pro's like myself, this furnace is a Coleman Evcon, Standard Blend Air II (there is also a more complex Deluxe Blend Air II furnace). Contractor was not familiar with it - I did some google-ing. This Standard model furnace has only a roof vent with a flex duct leading down to the furnace closet where it terminates at the upper left corner of the closet compartment, with an adjustable damper at its end, controlled by a motor (the Deluxe model has an attic fan and a couple of control boards, plus more switches in the furnace closet).

So, for this Standard model in question now... when the blower is on, this damper is opened to introduce fresh air into the home. The front panels of the furnace are vented (with filters) and the blower draws the fresh air into the cabinet and over the heat ex-changer and out to the floor vents (this is a mobile home). I've described this system, in case it's possible that this Fresh Air component could have anything to do with the flame shutting off prematurely. In retrospect, maybe I should have temporarily disconnected this Fresh Air component from the thermostat, or wherever it's connected to, to see if it was the problem.

The front of this furnace was very dusty, including the top surface of the control board, which was mounted horizontally in the box (labeled "A" in the picture). Neither the contractor nor I, ever did clean it (he didn't get a chance to - furnace starting working after his recall work). All I did was to remove and re-attach the two multi-pin connectors on the board in case they were not making good contact. I had also removed and re-connected connections at the Combustion Air motor, and switch or whatever that thing below the motor is called. Maybe that component proves induction air after achieving certain RPM speed of the motor (read about that somewhere)? I had also separated and reconnected the connector on top of the rectangular box ("A", in the pic).

If all the dust wasn't a factor, maybe the flame sensor circuit had a better ground after all the dis-assembly and re-assembly of the furnace walls, during the heat ex-changer replacement?
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Re: Coleman lights up, but shuts down soon after...

Postby DaleM » Fri Nov 30, 2012 11:03 pm

Coleman put out a service bulletin years ago about removing the Blend Air component if it caused any erratic furnace operation. I would go back, disconnect/remove the Blend Air and tape off the fresh air intake at the top left of the furnace.

Not sure what happens but the board in the Blend Air box interacts with the main control board causing strange things to happen. I didn't even think about the Blend Air system causing your problem..SORRY!! I have seen burners turn off mid-cycle before the blower every come on, blowers turned on without the tstat calling for heat, and my favorite and toughest one to track down, runs great for 3 or 4 cycles then nothing. I've hung temporary Tstats over hallway doors for up to a week at a time to be sure the problem was the Blend Air. Pull that thing off before it starts doing crazy things again.

BTW were there any holes in the heat exchanger?
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Re: Coleman lights up, but shuts down soon after...

Postby justplumducky » Sat Dec 01, 2012 6:38 am

Not sure what happens but the board in the Blend Air box interacts with the main control board causing strange things to happen. I didn't even think about the Blend Air system causing your problem..SORRY!!


No apology necessary, and I left out the part, initially, about me trying the startups with the Blend Air switch turned on (and getting the erratic blower operation), which would have made you think more about the Blend Air then, no doubt. Anyway, just grateful for your help. I learned a lot.

Also learned a lot while watching that heat ex-changer replacement. There were no holes in it. It was in pretty good condition, inside and out.
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