coleman furnace

[knucklebuster]

I went on a service call today & homeowner said that furnace would come on & run for @ 30 seconds & then shut off.The furnace is going through the complete cycle 1.The IBM is coming on 2.the HSI is coming on 3. the burners are lighting & running for @ 30 seconds & then the furnace is shutting off. I checked the ground on the furnace,the high limit, the pressure switch & tubing,& all were ok. I will say that once when the IBM was cycling on is when it did this. Any help would be appreciated!

Coleman-Evcon furnace- Model#BGU 075 12A
Serial#981165134

[coolwhip]

Does this person have a supply vent blowing right at the stat? 30 seconds sounds pretty short. what was the temp. rise?

[Shophound]

Did you try pulling the stat off its subbase and jumping R to W to see if the burners stayed lit longer than 30 seconds?

[gje1]

Did you try to jumper the pressure switch and if so does it stay running? Problems with Inducer fan or vent piping? Spider web in portal holes? After ignition sometimes they fail due to combustion and the inducer fan can't sustain enough vacuum to hold the sw closed. Also Coleman Evcon has a recall. Was that one of the model numbers?


[Edited by gje1 on 01-18-2005 at 12:12 AM]

[coolguysfl]

And the heat anticpator is set to ___?

When the unit cycles down, do you still have control voltage to the control center?

[knucklebuster]

I didn't check the pressure switch to see if it was holding. Can you just jump across the 2 wires on the switch with a jumper wire to check it? Also after the unit cycles off I still have voltage to the board.

[lalo56]

jump C to NO on Psw will close the NO sw. You can also try sucking on the tube yourself leading to Psw and see if burners stay lit to rule out Psw. You can also check what pressure you are getting with a magnehelic and see if it corresponds with the Psw.

[gje1]

Yes you can put a jumper across the terminals on the pressure switch. If the unit stays running than you'll have to diagnose is it the pressure switch or a problem with the inducer fan or vent piping. I'm only a Gas Serviceman for Pacific Gas and Electric Company. I visit this site to read and learn more about the industry. When I read about your problem it seemed all too familiar what I find in the field. I have only seen an inducer fan (blading) once. It was plastic and very cheaply made. The products of combustion have a lot of crap in it. The housing for the fan was extremely corroded with deposits. I digress, so what ever you have to check, per manufactures specification, vacuum from the inducer fan and airflow out of the inducer fan that will help you decide. Is it the vacuum switch or is it the inducer fan/ vent piping restricted.

P.S. I hope you just don't start changing parts. That's not fair to the customer or the profession. With the proper tools and proper knowledge no problem can be overcome.

[mikemich]

Flame sensor.

[Chad711]

Rusted out chimney, flame sense loss... Mark it.

[mo-flo]

had kind of same problem today with unit installed a couple days ago........every once in a while the inducer motor would make humming sound like bearings or something......tightened screws that hold it in place and took cover off and checked for blockage....although i didn't pull the little inducer motor...it just happens every once in awhile is the thing.i am betting bad bearings....gonna dig deeper.this unit even had new style of pressure switch and new roof jack.....it has small pitch to roof on this modular home.........has anybody else had this problem?

[ct2]

have you gone to the Colman website and read about the colman-evcon recall ?

[coolhye]

check the flame sensor or the flue , there might be a birds nest at the top.