bryant gas furnace burner wont stay on. - DIY Chatroom

pipebender · 11-05-2009, 11:52 PM

first i want to say awesome forum here i found it via google. i did a search and could not find the same exact problem im having on this old furnace. i have a bryant gas fired furnace model number 394dac024080 and first time of the year i went to use it. the burner will start and stay on for about a minute then turns off and it will keep cycling like this as long as the thermo is calling for it. the blower stays on. i thought maybe it was the thermo so i jumped out the red and white and same thing. runs for a minute and keeps cycling on and off. i am getting 29vac at the red and white. filter is brand new. pilot light light is on. this is in a 2 fam house so the same unit is right next to it. so im trying to compare the 2. 1 works no prob the other is this prob im having. i am a auto tech and have mechanical reasoning and electric background. i fixed the blower on the other unit 2 years ago. i been trying to find a wiring schematic of some sort so i can figure if the gas valve is getting proper power or how power flows thru this thing. if someone can leed me down the right path of the diag would be great. if there is flow chart i can follow? like i said i can swap parts from the other unit to problem solve. any questions i can run down stairs to check. i know this unit is a oldy but i have money probs at the moment jus got laid off. if i can save money atm would be great without a tech coming out. thank you guys in advance for any help! and btw I got this fancy thermo control unit that the gas company can limit ac in the summer dont know bout the winter. i have i feeling it may have something to do with that. but i called the gas company and they said i need a tech to come in first have him do the diag but if it is the thermo im going to have to pay for a service call but if i figure its deff the thermo then the gas company for free will come in and change it. the thermo wiring comes from the thermo upstairs to a control box in the basment then goes to the furnace. it says carrier on got sum circuit board in it with a antenna that says motorola on it. i can also tell you the wire colors goin to the wj4gxy if needed. sorry im rambing but just want to tell you guys everything i know at the moment. any questions ill be sitting on this topic so i can give a quick response. thanks again.
cheers,
jim

Houston204 · 11-06-2009, 12:41 AM

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?

pipebender · 11-06-2009, 01:00 AM

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.

pipebender · 11-06-2009, 07:55 PM

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?

Houston204 · 11-06-2009, 08:35 PM

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?

yuri · 11-06-2009, 08:36 PM

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.

Marty S. · 11-06-2009, 08:47 PM

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

Houston204 · 11-06-2009, 08:47 PM

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

How about blue..

yuri · 11-06-2009, 09:00 PM

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.

pipebender · 11-06-2009, 09:28 PM

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?

yuri · 11-06-2009, 09:52 PM

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.

Houston204 · 11-06-2009, 10:08 PM

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

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

Houston204 · 11-06-2009, 10:18 PM

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

Is this the furnace in question...

pipebender · 11-06-2009, 10:54 PM

yes houston looks just like that i also found this pdf http://www.xpedio.carrier.com/idc/gr...s394d.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......

pipebender · 11-06-2009, 11:09 PM

heres1