Bryant Carrier 90+ will not fire

[Showkey]

Bryant 90+ Plus 2 stage NG furnace will not fire when vent line in the side of the gas valve is connected. Furnace is 17 years old.
Background:
Default code 14 ignition locked out
First code is 34 ignition proving fault leads to 14 after 3 fails.

The the igniter glows, pressure switch closes, cleaned the flame sensor but the problem is no gas flow on start up. Once it fires it runs fine.
Checked and double checked vent and fresh pipes. Blew and sucked more than once.
If I disconnect the vent line to the side of the gas valve unit starts and functions.

Picture show the line in question. This vent line connects the fresh air supply, the side of the gas valve and the switch side of the pressure valve.

I swapped the inducer blower with a spare as a test. Same problem. I was suspecting the pressure switch but now thinking no ????

After working on this and watching this for hours I am thinking the gas valve is failing.?????

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Brass fittin on the side of the gas valve. Removed and checked the little port on the fitting it is clear.

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Green tape IDs line in question

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[zmaxmotorsports]

Ive never seen a gas valve with a vent like that.

 

[dreasoner]

Is this a 2 pipe vent system? If so, Have you checked the intake air pipe for ice buildup?
Will the furnace fire if the intake is loosened inside the furnace? This was a problem on early 90% installs that were at max conditions on the length of pipe or number of 90's in the system when outside temps were low as they are probably now in WI. The simple fix was to loosen the intake until outdoor temps warmed up. Concentric terminations do not seem to have as many of these problems.

 

[gregtwojeeps]

Ive never seen a gas valve with a vent like that.

It looks like a "two stage" gas valve somewhat. One that allows low pressure flow on ignition then converts to high pressure flow on flame. They were on Raypak boilers on some older units. Don't know if they ever put them on residential HVAC though ? When they failed it was usually on ignition, and had to be replaced. A schematic on the cabinet of the unit may show what type valve it is.

 

[Showkey]

Thanks for the input and things to check.


I have checked and double check both pipes. I have run a wire snake on both pipes. Shop vac and compressed air on both pipes. This is realtive short run on both pipes.

This is a new problem, it is cold here, nothing like real winter. Currently running 12-28* this has functioned as vented down to -30* actual temp.

I was thinking an intake pressure issue. The way I found this hose as the issue, I fired the unit with the burner front removed it fired fine. I do not have a manometer but but a tube with water into teed into to the line in question and the water in the tube does not react.
I can remove the line in question at any location and it will fire. I am pretty much confidence is is gas flow issue at start up.

Removing the fresh air vent pipe has no effect.

I did replace the draft inducer blower as test thinking many it was slow.

There is a video on youtube dealing with pressure switches. His gas valve has the tap or vent but he does not say what it does. There is a bleed hole in the fitting.

It is a two stage gas valve and it works on both stages.

Gas valve up close

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Port up close

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[Showkey]

This looks like my valve:

http://www.ebay.com/itm/like/111493...7290-0%26rvr_id%3D935328948372&chn=ps&lpid=82

 

[Showkey]

UPDATE...........

Not celebrating yet........but.........looking at the troubleshooting on the panel and two locations found online. They mention low gas pressure muntilple times in multiple locations for this problem.

The rubber line in question best I can tell is a feedback signal from the manifold to the gas valve.
When it does start the flame does sputter at first. My new theory is the low stage gas pressure is border line low and removing the feedback signal gets it just up enough to fire.

So.........adjusted the low stage stage pressure UP slightly. One of the PDF instructions for the valve shows adjusting this low pressure setting.
So ........far it's been starting with all the lines in place........with no sputter.

 

[98ssuck]

Take the inducer fan off and check the secondary heat exchanger. Those furnaces are notoriously bad at plugging them. You can build a utube manometer to check the pressure or vacuum on the inducer fan.

 

[Showkey]

Monday update:

Faulted again his morning. Called a Bryant dealer.
Technician spent three hours and several calls to tech support. Not make progress, problem seen often same operation it get it to light. After disassembly of the burner the problem actually got worse. Problem is have gas ( flow and pressure) have ignition source but no flame. Everyone is shaking their head.


The shop owner came........went over things again. He suspected a burner problem like irractic gas flow/mixing to the igniter. With the burner box cover off, at ignition start, he blew a puff air at the first tube, burner lit every time. Remove burner tube assembly again and cleaned the burner tube disks and the slots between the burners. They were not all that rusty or dirty......but

Problem fixed, root cause poor gas flow toward the igniter at start up.
Reset gas pressure back normal. Combustion check, pressure checks, CO test all good.

Now when it starts the burner sounds even and controlled at start with no flutter.
Going to replace the burners tubes as a precaution.

And monitor ......


http://www.repairclinic.com/vwo7/Pa...mber=355MAV042080AAKA&ss=a36b370d1459010&mr=1

 

[dreasoner]

I worked for Carrier as a product support engineer on the ICP side during the early 2000's. There was indeed a problem with the crossovers on some burners causing the problem you described. The easy fix was to regauge the crossovers by sliding a piece of 20 gauge sheet metal thru them to ensure they were opened up to factory specs. I don't remember what the decimal equivelent is off the top of my head. Hope this helps someone.

 

[CNGsaves]

So in a nutshell, was it starving for air, or starving for fuel ??

 

[Showkey]

So in a nutshell, was it starving for air, or starving for fuel ??

Not sure.......guess the tubes get the mixture right and pointed in the right direction.......SO......... Again guessing the puff of air leaned it out ?? Or did the puff get the mixture to the igniter ?? Or a little of both which made it so irractic.

 

[Rockhead261]

Just saw this thread... sorry I'm late, but.... I have the same type furnace in my attic. When it was two years old I had a Praying Mantis commit suicide on my ignitor and burners by getting sucked in through the combustion air tube. His remains cracked the HSI, fouled the crossover vanes, and caused all kinds of havoc in the burner section. I replaced the HSI and disassembled and cleaned the burners - gently - then reassembled. Upon seeing marginal crossover ignition I took them apart again and opened the crossover gap slightly with a flat blade screwdriver. That was in 2000. It's been running flawlessly since.

FWIW, it's a 104K BTU model that I have slightly derated, running at 3.0" W.C.

 

[dreasoner]

The problem with the crossovers was that the fuel/air mixture did not travel consistently along from one crossover to the next. You can get the same problem if the crossovers are not in the same plane. Taking the burner box cover off or blowing on the burners help the flame travel from burner to the next. It does not take much of an adjustment to fix the problem caused the narrowed gap from the debris. With ribbon burners found on old 60% furnaces, **** in the burners would cause delayed ignition usually with a loud boom present.