Home Repair Forum

cids292 · #1 (**permalink**) 02-20-2008, 10:02 AM

I have been having a intermitent problem for sometime know. I have a Bryant plus 90 model # 398aaz036080. Sometimes the furnace comes on and works fine for days and sometimes it won't come on at all. If I turn the power switch off then on it will work fine for a while. Any suggestions on how to start to fix this problem?

Java_Bob · #2 (**permalink**) 02-20-2008, 11:43 AM

could be allot of things, loose wiring, circuit board going bad etc. best to have a VOM and do some checks when it happens

HayZee518 · #3 (**permalink**) 02-20-2008, 12:46 PM

there are some identical problems to your post elsewhere in here. check them out. a control board seems to be the main problem.

cids292 · #4 (**permalink**) 02-20-2008, 08:35 PM

It also appears to run for about 5min then shut off for ten minuites fairly regularly. It is very cold now about 5 deg that mayt have something to do with it. Is that normal? I don't remember it running that often. I should also at that when it doesn't come on nothing comes on not even the combustion blower. Any ideas please help.

mike n · #5 (**permalink**) 02-20-2008, 09:21 PM

When the system shuts off it is in lock out the control board is reading the entire safety circuit and diagnosing the problem for you there is probably a flashing light that will tell you where to look (open pressure switch, flame failure, etc.)
Before you turn the power off look for a failure code look for a sight glass in the blower door it will give you a flash code then if the installer put the wiring diagram on the door like he was supposed to it will give you the legend for the flash codes (3 flashes flame failure, 4 flashes pressure switch open etc.) if you tell me the flash code I can tell you where to look

cids292 · #6 (**permalink**) 02-20-2008, 10:09 PM

This unit is old enough that it has no LED to flash codes. I do have the wiring diagram but I do not know what the voltages are suppose to be and where. Thanks for the help.

hvacwiz · #7 (**permalink**) 02-21-2008, 09:01 PM

Condensate trap plugged up?

mike n · #8 (**permalink**) 02-21-2008, 09:01 PM

If you do not have a pc board with diagnostic codes you should have a sequence of operation on the wiring diagram but if not I need to know what you're seeing.
Does the furnace start at all or does it just sit there? What kind of ignition (spark or hot surface)? Does it have a draft inducer ( a small fan motor in front of furnace creating draft to get combustion product out of furnace) or is it natural draft?
If it has a draft inducer and it does nothing after a call for heat then it may be a pressure switch it could be the switch bad or the fan bad. If this is a 90% furnace I have a hard time believing it has no pc board I would look again is it possible that it is not a plus 90
As you can see it could be alot of things so we need more info, let me know

cids292 · #9 (**permalink**) 02-22-2008, 08:32 AM

The condensate drain is not plugged. There is not a sequence of operstion on the door panel with the wiring diagram. When the furnace fails nothing happens it just sits there. I think the ignition is a piolt lite that lites off of a sparkplug type device. It does have a draft inducer fan. It has a pc board but there are no LED's on it. It says Bryant plus 90 on the door cover. There are 3 pc boards one I think is the main board with the relays and where the thermostat hooks up and where main power comes in the other one is hooked up to the pressure switch and one that is with the igniter and gas valve. I should mention that the furnace has worked fine for 3 days now.