Trane Gas Furnace Problems

[fixer]

Hi Guys,
I need help with a Trane Model TUC120C960B7 LP Gas Furnace. The furnace is laying on it's left side with the hot surface ignitor at the top and the flame sensor at the bottom. The problem is sometimes on a call for heat the inducer powers up then the hot surface ignitor glows then the gas valve opens and only the top burner ignites the goes off.
I changed the gas valve and converted the valve to LP by changing the valve spring. The inlet LP gas pressure is 12 inches of wc and the outlet pressure is 11 inches of wc.
I also pulled the burners and cleaned them and made sure the crossovers were clean and in line with one another.
I got the burners firing better but they fire from top down to slow and sometimes will not make it all the way down to the flame sensor fast enough before the flame sensor cuts it of.
Any ideas?????????
There is another Trane furnace in the same crawl space same model but 80,000 btu working fine.

[berad]

clean the orifices.

[tinknocker service tech]

is there a drip leg on the gas line before the valve. if not clean and oil or water out of the manafold and clean the orfices

[wally01]

These are the things that I would question. Are the orifices you installed ( I'm assuming you did put in LP orifices out of the kit) indeed lp orifices? Are the pressures that you are reading taken at the same time as the valve is opening or after the furnace has fired and run? If the gas pipe is too small it might not be able to supply volume at the moment of ignition causing pressure drop and flame failure. Unit level? Anything plugging manifold? Some silly things like clean flamerod, plugged heat exchanger ( although pressure switch should catch that), installed on correct side ( I can't remember if there is a wrong side on TUD's I really only put in TUX's).
You can always call Trane tech support. Sometimes they can save your butt when trouble comes calling.Good luck

[fixer]

Thanks Guys
The orfices are clean I checked them when I cleaned the burners. They are the right orfices. There is a drip leg before the gas line enters the furnace.
I will go back tomorrow and double check the gas pressures using a pressure gage on the inlet and a pressure gage on the outlet at the sametime to make sure of no pressure drop during start up.
I checked the installation manual from the Trane Comfort Site and the furnace is installed on the side it is intended to be installed on.
I agree with you Wally it may be pressure drop.
Thanks

[Edited by fixer on 11-03-2005 at 07:52 PM]

[berad]

Could be the igniter is not hot enough or to far away from the burner too.

[mrssb]

Have had a similar problem with some Trane furnaces, have switched to stainless burners, and the problem has went away. Not saying it will solve your problem but it might be worth considering.

[berad]

Originally posted by mrssb
Have had a similar problem with some Trane furnaces, have switched to stainless burners, and the problem has went away. Not saying it will solve your problem but it might be worth considering.

Those burners rock, I include them in all of my new lp installs. They will outlast the heat exchanger by far.

[1972torino]

check the pitch! be sure it is draining

[airconman]

pull all the burners and clean em. Thats my vote.

[comfortable air]

how long the flame lasted? if it is not more than 3 second it could be back pressure problem. if it is lasted the flame sensor sense prove time( maybe more than 5 second, I am not sure), it is flame sensor or ignition module problem

[james mo]

12" input and a 11" wc manifold---I thought those gas valves had a minimum of 2" wc drop over them. I would be checking the inlet pressure when the gas valve opens.

P.S. Wouldn't it make more sense for the hsi to be on the bottom and the flame sensor to be on the top? Flame would spread more readily. Can you change the component locations on these furnaces?