Bryant Plus 90 Burners kicking on then off

[dw9663]

Can anybody describe the characteristics of a bad gas valve on the Bryant Plus 90 furnace? I have limped the furnace along, but the problem, same one as described above still persists. I have replaced the flame sense and it did not really make a difference.

In it's current state, it takes about 30-40 mins of cycling to actually get the furnace to turn on the main blower and then heat the house. About half way through a heat cycle, the furnace will basically quit like it has reached the set temp on the stat but is actually still a few degrees shy (the gas flame shuts off and the main blower runs for a couple of minutes to complete the cycle). Then it goes through the fire up cycle again numerous times before it heats again. I have the cover on the burner box off as it seems to run better with warmer air. I checked and have not found any restrictions in the system.

The furnace is a 1986 model, any idea on expected life of such a unit? I am debating whether to consider a new furnace or repairs to this one.

[paul52446m]

to have any shot of having these furnace to work right you have to do this Check the gas pressure both incoming and header side. there is a indent in the metal under the pilot ass.
drill a small hole in the bottom of this indent to let any moisture drain out so it wont short out the pilot ass. you have a separate pressure reg on the gas value for the pilot gas, turn this pressure up as high as it will go, this should help. Make sure your pilot is real clean. Taking the door off is not the answer. put the door on and get some washers or coins and start cutting down the air intake. Put the coins on the screen in the air intake, you might have to cut the air in half. The reason you are doing this is when the main burner comes on it pulls the flame away from the pilot switch and the pilot warp switch cools down and kills power to main gas. The inducer is pulling to much air through the burner area. make sure you turn that pilot pressure all the way up. later paul. Stay in contact and maybe we can get it fixed

[dw9663]

Bryant Plus 90 Burners

To close the loop and for anybody troubleshooting, turns out the vacuum line was plugged at the heat exchanger. This basically slowly deteriorated the vacuum signal to the point that the flame sense and burners would not activate. There is also a rebate on a Bryant Plus 90 burner due to a defect so you can get back about 1/2 of what it takes to replace it. The issue is the material used as a sealer, which ends up plugging the vacuum line. On the main fan motor, there is also multiple speed options as a setting, so if you need more / less fan speed, that is available. 4 is slow, 1 is fast.

[HayZee518]

THANK YOU for the feedback. I'm sure others will benefit from this. Maybe we should start a sticky thread on this type of burner to include symptoms and fixes. Eventually it will look like a flowchart troubleshooter and remedies.

[dw9663]

That is a great idea, the one thing I have trouble finding is a troubleshooting guide or manual for the unit. I have poked around a bit on the web but can't seem to come up with a manual. Any recommendations on good sources for a heat exchanger?

[HayZee518]

dw if you could find me a ladder type schematic diagram for this or any generic furnace of the same make we could start a point by point troubleshooting chart. BRYANT seems to be the most common heater.

[dw9663]

I will work on that, I don't have one other than what is stuck on the door of the furnace itself.

One other question, does anybody know if you can extend the run time of the blower on the auto setting after the furnace shuts off. If I run the fan for another 2-3 minutes I push out a fair amount of left over heat. Thanks.

[HayZee518]

try adjusting the plenum limit switch proportional band

[paul52446m]

I will work on that, I don't have one other than what is stuck on the door of the furnace itself.

One other question, does anybody know if you can extend the run time of the blower on the auto setting after the furnace shuts off. If I run the fan for another 2-3 minutes I push out a fair amount of left over heat. Thanks.

You will have to look on your electronic board and read your book, it should tell you how to make the timing longer on your blower cycle. If you can't find this
info, if you give me model and ser. no. maybe i can convert them to payne
model no. I sold Payne for years and they are the same as Bryant.
later paul

[dw9663]

No book, not much on board. A white knob indicating longer or shorter delay on right hand side of main board. Not sure if that is for running the motor after the burner stops or a delay in staring up the motor after the inducer fan runs.

Model: 398AAW048100ADBA Product: 398AAW048100D
Serial #: 5385A57774

It's an old unit, circa 1985.

[paul52446m]

the longer timing is for the blower to run longer after the burner turns off. paul

[paul52446m]

i will see what i can find out on the recalls, and if there are manuals available. Later Paul

[dw9663]

Thanks, much appreciated. I adjusted the knob for the delay up to the max position, did not seem to have a great effect, maybe some, but there is still heat left in the ducts, particularly at the burner exit when the fan shuts off.

[HayZee518]

just for laughs take a look at the current rating of the gas valve and make an adjustment at the thermostat's heat anticipator. this in effect extends or shortens the cycle time of the burner.

[marasca]

Bryant Plus 90 furnacengoing problem

I would really appreciate any thoughts or guidance on an ongoing problem with my Bryant Plus 90 High Efficiency gas furnace (Model 35MAV036080, S/N 0397A00985, installed 3/13/97 in Washington DC metro area).

In addition to regular maintenance by the company that installed it, I’ve had two service contract visits from their staff recently, for a problem that we can’t seem to resolve: The furnace will start the first phase, where it sounds like it’s drawing air in, but never goes any further. It just shuts off until the next time it tries, with the same effect, and will try sporadically throughout the day if I don’t turn off the thermostat.

On the first visit, a code 31, “Pressure Switch will not close or respond,” per the owner’s manual, was noted by the technician. Per the invoice, “checked pressure switch and found intake hose was cracked. Repaired hose and ran unit, everything seems to be working good now” and it was operational again.

A day later, the error code was back – then disappeared for a few days, only to return permanently.

On the second visit, the (different) tech that came, after checking the outside vent for blockage (none), noted on the invoice that the “secondary heat exchanger trap clogged – pulled trap hoses – drain secondary heat exchanger – cleaned trap – reinstalled – start system. Cycled several times OK.”

That was last night, and now the unit is offline again, with the same code 31 flashing on the LED indicator.

I’ve read this thread carefully, and am wondering if the symptoms might related to what was described in post #18 of this thread (haven't been able to find any more recent threads on this topic.)

However, any thoughts at all would be greatly, greatly appreciated, with the understanding that you aren’t onsite.



Thank you!