32 replies to this topic

[hyprdrvr]

Flame is blue from tip to toe. Long shot showed 122VAC input with unit off. Lowest reading was 119.5VAC when blower and igniter were running at the same time. Input voltage seems to be ok. Ohmed the sensor & wire. The meter leads have 0.14 ohms of resistance. Testing from board to any joint in wire or tip of sensor gave a reading of 0.30 ohms.

[jb8103]

Everything is nominal except the FR current. All that remains is a manifold pressure check, which I just know is going to be 3.5 WC, and a description of the FS lead connection to the board (pretty please with sugar on it), which I just know will be clean and solid.

My last bullet has the board's name on it. Getting a bad one off the shelf is rare but it does happen.

You wouldn't happen to be anywhere near Canandaigua, New York, would you?

Edited by jb8103, 25 October 2012 - 04:42 AM.

[jb8103]

Next to last bullet, that is.

I always keep the last one for myself.

[Budget Appliance Repair]

That burner looks exactly like a Coleman I worked on 4 or 5 months ago and I did much checking for what the microamp ratings should be and almost everything I came up with was between .1 and 2 mircoamps was all that was required, (one had specs of 5). The controller that I used as a replacement (RobertShaw HS780) was spec'ed at 1.5 mircroamps.

Was doing almost the exact same thing you describe here except not getting the longer run times, just shutting down after the 6 second flame sense period.

Ended up be the control module, I would almost be willing to bet that is your problem also.

Attached is a PDF document about FLAME RECTIFICATION for furnaces and how to measure with specs for Fenwall module, (the only one with a high 5 microamp current required), and some Johnson Controls and White-Rodgers modules.

Attached Files

•  Flame Rectification Info.pdf   29K   6 downloads

Edited by Budget Appliance Repair, 25 October 2012 - 08:01 AM.

[jb8103]

Not that I'm arguing, but I have never seen a furnace with microamps that low. Always 5+, or I replace the sensor. I can't bring myself to trust one tenth of a millionth of an amp.

Bears looking in to, thanks, Willie!

Edited by jb8103, 25 October 2012 - 05:59 PM.

[Bullstok]

i have had many where the burner was a little dirty (or turned slightly grey) and i increased the reading several microamps by cleaning the area of the burner where the flame comes out from (3m scotchbrite pad). not saying that is absolutely the problem. but something to consider if the grounding of the burner has already been checked. also once in awhile the flame sensor rod gets glazed and touching it a little with small very fine file will help. (don't leave gouges, just very lightly)

p.s. a lot of boards only need 1 microamp

Edited by Bullstok, 25 October 2012 - 09:50 PM.

[hyprdrvr]

No luck on the manometer. At this point, everything leads to the new control board being bad. Ordered it online and missed the little note about no returns on circuit boards. I have emailed the manuf. (icm controls)...waiting for a response. Also,the temps have finally dropped to low 40s here in NW Louisiana, so I called the local coleman service tech. The will be here early next week to look at the recall issue. I'll have them figure it out if the manuf. can't/won't help me out.

[jb8103]

There is one thing left, stray voltage on the neutral.

[hyprdrvr]

How do I check that?

[jb8103]

Neutral is grounded at the panel. If there is any voltage between neutral and ground inside the furnace cabinet you have a wiring problem somewhere. I only mention it in case you did not specifically check for it when taking the long shot. It's just that voltage on the neutral, or ground of course, would definitely have an effect on our microamps.

Don't worry about the manifold pressure if your flame characteristics are good. Which they are.

That's all I have, hyprdrvr. Bon chance, and if you do get to the bottom of this, post back, won't you?

P.S. Use that borrowed Fluke meter to check this, you need a true RMS meter.

Edited by jb8103, 28 October 2012 - 07:23 PM.

[hyprdrvr]

Will do on the resolution post.
Don't have the fluke on hand. Bought a Klein MM200 to replcae the GB meter that was not reading amps correctly. Should have bought the MM2000 but did not think I would need true RMS or Low Impedance. Anyway, It's reading 0.074 VAC and 0.5 mVDC between house ground and neutral on control board.

[jb8103]

Sheesh, that's cleaner than usual.

[Daveb1972]

All furnaces that use flame rectification are sensitive to propper polarity. Chech the 110VAC supplu (black) to ground, and the same Neutral (white) to ground. If they are reversed this will occur.

flame sense values above 1.5 UA are usually enough to keep the control happy. I'd try to check burner ground as well, right where the flame would complete the circuit t ground from the flame sensor.