# bryant gas furnace burner wont stay on.



## Houston204 (Oct 18, 2009)

Is this an old furnace?
Do you have AC as well as heat?
Sounds like you are tripping a limit.

Do you see this fan limit in your furnace?


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## pipebender (Nov 6, 2009)

thanks for your response! yes ITS very old 1974. the ac side works no prob. i forgot to mention when it calls 4 heat the blower does come on. i see the fan limit switch which looks a little different then the pics. mine looks like both of them on top of each other.


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## pipebender (Nov 6, 2009)

im going to switch out the fan limit switch in morn with the one from the other unit. if the fan limit switch is bad would it still give 26vac to the gas valve? cause when the burner ignites it gets power then when power cuts off so does the burner. someone was saying it could be the thermocoupler where is that? does my old unit have this?


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## Houston204 (Oct 18, 2009)

I doubt that anything is wrong with your fan limit. It is probably a low airflow problem causing your fan limit to cycle your gas valve this way. Can you see the inlet side of your evaporator coil?


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## yuri (Nov 29, 2008)

The sequence of operation is usually 1 of 2 methods. The limit control supplies 110 volts to the transformer which powers the thermostat and then the gas valve. Or the limit control is in the 24 volt circuit to the gas valve. Sounds like the unit is cycling on the limit control from a lack of airflow. Fan running too slow, dirty A/C coil or the limit control is weak from being tripped too many times over the years.


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## Marty S. (Oct 31, 2009)

Check the heat exchanger before you put any money in a 35 year old furnace.


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## Houston204 (Oct 18, 2009)

Looks like we were thinking the same thing.
Ever miss the Sheriff?










How about blue..


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## yuri (Nov 29, 2008)

I couldn't get my da*m monkey to load as my profile. LOL. Click on my name and profile to see my handsome mug.:thumbup:


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## pipebender (Nov 6, 2009)

the a/c coil is clean. should i pull the fan switch to see if the probe is dirty? the blower sounds good its just blowing cold air in the house. how do i check heat exchanger? pull the blower out? should i try with blower door off?


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## yuri (Nov 29, 2008)

Post some pics of the furnace, burners, fan control,wiring etc so someone may recognize that unit and what we are dealing with. Click on GO advanced, manage attachments and follow the directions.


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## Houston204 (Oct 18, 2009)

If this is a vertical furnace, the dirty side of it isn't easily viewed.


It wouldn't be the top of this coil...


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## Houston204 (Oct 18, 2009)

Your pic's file size is too large...











Is this the furnace in question...


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## pipebender (Nov 6, 2009)

yes houston looks just like that i also found this pdf http://www.xpedio.carrier.com/idc/groups/public/documents/techlit/pds394d.50.1.pdf

i just to6k pics im going to post in a sec6nd thanks for your help guys. money is real3y tight and n6w t6day i found out my girlfreind just got laid off too godamn econmy......


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## pipebender (Nov 6, 2009)

heres1


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## pipebender (Nov 6, 2009)

heres-two


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## pipebender (Nov 6, 2009)

and-heres-3


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## pipebender (Nov 6, 2009)

electric company put this in so they can control stuff.


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## Houston204 (Oct 18, 2009)

Can you see the inlet side (bottom) of your vertical coil?


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## pipebender (Nov 6, 2009)

Houston204 said:


> Can you see the inlet side (bottom) of your vertical coil?


how can i see? from downby the blower? i tOOK off the panel on top for ac coil and its clean.


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## Houston204 (Oct 18, 2009)

The triangular panel in the center of your A coil will allow viewing of your inlet side.

Removing the blower and snapping some pictures through the heat exchanger would be less likely to cause a refrigerant leak if the A coil center panel is blocked by too many feeder tubes.


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## yuri (Nov 29, 2008)

Check the rating sticker in the furnace. Should tell you a recommended temp rise thru the unit. Ie 40-80 degF. Do a temp rise test. Check the supply temp a foot downstream from the plenum and subtract it from the return temp. That black box is a combo fan/limit control made by camstat and fail a lot when old. I would not swap the other one from your other furnace as it is so old and brittle it will probably fail and then you will need to buy 2 of them. Should still be available (Johnstones/Grainger)?. Check the coil for blockage if you can. SERIOUSLY, you need 2 NEW CO detectors for your house as the heat exchanger is NOT in good shape and may be cracked. One for your bedroom, the other in a stairwell going upstairs from the basement.


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## mrairflow (Oct 25, 2009)

i would recommend you call somebody that knows what they are doing to check that furnace ,i have found many of them with the heat exchanger rusted out. also do you have to add freon to that system as it looks like oil on the bottom of the a coil . the part of the coil you are seeing is not the side that gets dirty it is the side you dont see try lifting up on the coil and look at the heat exchanger look for holes also look inside the coil with a mirror see if it is clogged


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## Marty S. (Oct 31, 2009)

Easiest DIY heat exchanger check on that furnace is 
1) turn off the power
2]remove the blower,camstat and burners
3) look inside the heat exchanger with a bright flashlight for cracks or excessive rust
4) wet down the outside of the heat exchanger from the blower compartment on up with water. 
5) look inside the heat exchanger again with the light

Any cracks or rust holes will show up as damp spot that was not there on the first visual inspection. Cracks usually happen along the back of the heat exchanger and near bends. There's no middle ground here, it leaks or it doesn't.


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## pipebender (Nov 6, 2009)

yuri said:


> Check the rating sticker in the furnace. Should tell you a recommended temp rise thru the unit. Ie 40-80 degF. Do a temp rise test. Check the supply temp a foot downstream from the plenum and subtract it from the return temp. That black box is a combo fan/limit control made by camstat and fail a lot when old. I would not swap the other one from your other furnace as it is so old and brittle it will probably fail and then you will need to buy 2 of them. Should still be available (Johnstones/Grainger)?. Check the coil for blockage if you can. SERIOUSLY, you need 2 NEW CO detectors for your house as the heat exchanger is NOT in good shape and may be cracked. One for your bedroom, the other in a stairwell going upstairs from the basement.


ok im going to try the temp rise test. i got a infrared thermo to use. i looked on grainger and i see one similiar. does this problem sound like a fan/limit switch? should i just order one? i got 3 co detectors in the house one is the basment one at the top of the steps and on by my kitchen cause i got a gas stove. if the heat exchanger is cracked would i still be getting a real nice blue burner flame? so my problem sounds like it had nothing to do with my fancy thermostat controller?


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## pipebender (Nov 6, 2009)

mrairflow said:


> i would recommend you call somebody that knows what they are doing to check that furnace ,i have found many of them with the heat exchanger rusted out. also do you have to add freon to that system as it looks like oil on the bottom of the a coil . the part of the coil you are seeing is not the side that gets dirty it is the side you dont see try lifting up on the coil and look at the heat exchanger look for holes also look inside the coil with a mirror see if it is clogged


i have not put freon on that side of the units in 16 years. im going to take the blower out and the a/c coil access cover to get a better look again.


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## pipebender (Nov 6, 2009)

Marty S. said:


> Easiest DIY heat exchanger check on that furnace is
> 1) turn off the power
> 2]remove the blower,camstat and burners
> 3) look inside the heat exchanger with a bright flashlight for cracks or excessive rust
> ...


im going to give that a try.


THANKS AGAIN EVERYONE FOR ALL YOUR HELP!


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## yuri (Nov 29, 2008)

The color of the flame won`t tell you if it is cracked. I would CAREFULLY inspect the heat exchanger B4 spending any $$ on repairs. The fancy controller looks like a load shedder to allow them to shutoff your AC in peak times and give you a lower $rate. Those camstats, fan controls fail a lot in old age. You need a cooking or stick type thermometer to insert into the airstream of the duct.

Good Luck


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## pipebender (Nov 6, 2009)

welly welly well!!!!! i changed out the fan limt switch from my other unit and it fired right up!!! so far so good. sucks for my tenants but im a slumlord...... lol i already told them the deal. thanks for everyone trying to help me. after looking at the wiring schematic i found on the net. i started measuring out points with my multimeter and comparing them to my other unit both calling for heat. i found the power stoped at the fan switch. this sucker lasted for a long time good lord. date stamp on it was 12/73 camstat 01-0584a stamped on the side. it dont even look up on there cross reference at camstats website i gotta call. looks like they aint based in cali anymore either cause stamped in mine says los angeles ca now they in chatem il. is there any way i can rebuild this switch or jus buy a new one? CHEERS!!!!


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## yuri (Nov 29, 2008)

Buy a new one, not rebuildable or SAFE to do so.


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