20 replies to this topic

[jb8103]

A friend of mine has this old Lennox gas furnace, serial #5873 (which I make out to be a 1973). It has four ribbon burners and a standing pilot. Hadn't been cleaned in 10 years so he asked me over to clean it up and check it. It wasn't that bad, surprisingly. I brushed and vacuumed the burners and burner chambers and changed the odd-duck filter. It fired up OK.

It has a large pilot flame, about an inch or more. The burners have four inch flames, mostly orange though, only blue at the roots.

CO in the stack was 8 ppm, efficiency 75.1% according to my Bacharach Fyrite 60, about right for an old natural draft beastie.

I don't like all that orange, though. Your thoughts? Do I need to seriously clean this thing?

[Bobice]

If the gas pressure is too high you will notice the tips of the flame much higher, pointed and orange in color. The orange gas flame color usually means there is too much gas for the air mix input. [Dust, debris, or other problems in the gas/air mix ratio, such as a mis-adjusted or blocked air intake at a gas burner will also change the flame color and pattern.]

[jb8103]

I really should have checked the output pressure while I was there. I had lots of excess air and nice clean stack gas, though. So I figured I'd check here first.

On this gas valve, the regulator adjustment and output port are on the bottom. I'll have to stand on my head.

[ACtechGUY]

You may also want to check that the air shutters on the ribbon burners are open enough. Not enough air will cause orange flames.

[jb8103]

I don't think these have adjustable shutters.

[Dan Webster]

Post some pictures of them burners and the gas valve if you can.

[jb8103]

I'll be back out there tomorrow. If I can't get the flames right I'll post pix. CO was very low (8 ppm) so I'm not too worried.

[jb8103]

Got back out there and super-cleaned with brass brush and vac. As I thought, there are no air shutters on these burners. My brand-new Fieldpiece manometer failed, so I couldn't get manifold pressure. Nice. Anyway the flames are now at least predominately blue with orange streaking, so I missed a lot of grit and grime the first time around I guess, but no sign of yellow in the flames. Pilot flame is a more reasonable 3/4 inch or so, healthy looking. Combustion analyzer reports 12 ppm CO in the stack gas and 76% efficiency.

Unless the experienced techs here say different, I think I can close the book on this one. You know what surprises me about this Lennox, it has no rollout switch. The wiring has no terminal strip, all is wire nut connected and shoved in the box with the transformer. Schematic is unreadable so I'm not sure if this is a later mod. Never heard of anyone discarding the terminal strip before, though. (?)

[ACtechGUY]

Maybe safety was not a top priority in the early 70's . Really OLD furnaces did not have anything other than a high limit switch (if you were lucky)!!!! . I had a customer with a late 60's lennox furnace who would adjust the gas valve so the flames would be about half as big. Those old lennox heaters really put out big some flames.

The wiring is probably factory wiring . for some reason manufactures used to cram a bunch of wires in a little box.


I would say everything is ok with this furnace

Edited by ACtechGUY, 07 January 2011 - 05:53 PM.

[RegUS_PatOff]

with a model number, we may be able to find the wiring diagram on-line..
You may be able to add some safety devices..
Does this house have a (few) CO detectors ?

[jb8103]

G1203-110 is the model number. All I can find online is this:

http://www.lennox.co...chived-docs.asp

User guides.

There's a PDF for the G12 Series in the list.

I can always sketch out the wiring and work a rollout switch in there. At a glance, they don't seem to be using typical color scheme though. Wouldn't want to make it easy on the new guys or anything.

My friend does have two CO detectors, mounted outside the bedroom doors according to scripture, but they are several years old. I advised him to upgrade to the latest Kidde in the $50 range.

If we trust our instruments, the combustion analyzer reports 12 ppm CO in the stack and 0 ppm in the supply.

But how much do we trust our instruments?

For example right now, in my office, a Fluke 902 reports ambient temp at 54F. An Ideal 61-310 reports 71F. A Fieldpiece ARH4 psychrometer hooked up to the same Ideal meter through the Fieldpiece adapter handle reports -59F. In reality it's probably about 65F in here.

[RegUS_PatOff]

G1203-110 is the model number.
My friend does have two CO detectors, mounted outside the bedroom doors according to scripture

1) maybe G12Q3-110 c.1980
G12_G12E_01-01-1980.pdf

2) CO detectors or smoke detectors ?
Some of the AC powered models have digital displays with continuous read-out

click on picture

[jb8103]

By jove, that's it. Q. I'm getting stronger glasses. Thank you!

He's got both smoke and CO detectors.

[jb8103]

Doesn't have a door interlock either, not that it's a big deal, one less thing for the homeowner to tape closed.

And that's the other thing guys, and I'm really curious about this: after I shut off power to the system, the main flame stays on for 10 seconds. Never seen this before.

[RegUS_PatOff]

By jove, that's it. Q. I'm getting stronger glasses.

My eyesight isn't as good as it once was (see RegUS_PatOff )

[Dan Webster]

[Budget Appliance Repair]

Some of these older furnace gas valves use a bi-metal gas shut off, just like the now days common gas safety valve in gas ovens with glowbar/hot surface igniters.

They can take a few seconds to open when power is supplied and also a few seconds to close when power is disconnected/t-tstat cycles off.

Looking at the PDF file that RegUS linked to it doesn't look like yours uses that style system though, but there is still a possibility depending on the main gas valve that is on your system.

[MrFixit246]

Sorry I am late to the party here. I guess i have been asleep at the wheel. Too much Overtime.

These furnaces are solid, if they don't crack along the compound curve in the back of the heat exchanger. I have yet to see a G12 cracked that is making CO because of the crack.

The yellow flame you saw first was probably dust from the cleaning. It can take 5 minutes to clear up and longer if you washed the burners.

As far as adding a roll out switch, I would not try to re-engineer the furnace, it only adds liability to you and usually makes the furnace break easier. K.I.S.S.

Finally the gas valve is a slow open slow close valve. There is an orifice on the regulator that causes it to be this way. If you ever have replaced one with a snap open valve you will usually get a delayed ignition type whoomp on start up.

'Fixit

[jb8103]

Wait a minute. I was looking for sliding collar air shutters. Looking at Reg's PDF, he just might have these rotating shutters.

I watched the flames for a couple of cycles and the characteristics did not change, so I don't think it's just dust making the orange. He might very well be running rich.

Anyway, what the PDF says is a shutter, I thought was just a crimped-on plate to hold the burner at the spud. Even if these things do rotate, how is that supposed to let in more air?

[Budget Appliance Repair]

The end of the burner has pie shape cutouts in the end the shutter covers. The shutter also has the pie shape cutouts which will open or close off the cutouts in the burner ends to give more or less air.