# Bryant Plus 80 Run Problem



## kenmac (Feb 26, 2009)

code 33 is limit. Does blower stay on when burners go out. May not be getting enough air flow.Looks like a new install. Is it under warranty ? If so call the installer. If you tamper with it it could void warranty


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## Nucon (Dec 8, 2010)

Not sure what PS means.

I did remove the hose and it is clear from obstruction. The flue vents through the roof. The unit is in the basement.


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## kenmac (Feb 26, 2009)

Take the filter out & see if it will stay on. If you use a thick filter it can restrict air flow enough to trip limit


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## Nucon (Dec 8, 2010)

I removed the two filters on the return air supplies. Seems like a faulty limit switch if this works.

I use the following filters. One each on the two return air supplies on the first and second floors:
Filtrete 3M 20x20 Purple Colored FPR9 Filter.


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## Nucon (Dec 8, 2010)

OK. So with the filters removed the unit ran a subsequent full cycle. 

But leaving the filters off can't be an adequate solution and I have used the same kind of filter for 3yrs now. Should I replace the limit switch?


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## hvactech126 (Nov 11, 2010)

b4 you get too much wrapped up in this furnace, the heat exchanger is know to crack. it might be best to call a pro and have it examined

the evaporator coil on top of the furnace might be plugged up as well

you can replace the switch, they do wear out, but might check evap coil first and heat exchanger


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## Nucon (Dec 8, 2010)

well. the Furnace is back to its old tricks again so I guess removing the filter wasn't the answer I thought it might be. I'm not sure what the heat exchanger is. Can you elaborate?

IN the meantime I had started calling for a new limit switch. I called a parts warehouse and the owner who used to do repairs said it sounded like an airflow problem. This would be in line with a stopped up coil and removing the filters. I checked the coil and its not dirty looking except at the top and I vaccumed it as best I could. I took this chance to look up the duct work and all dampers and the like look fine. I completely removed and dissasembled the blower for cleaning. While I was in the lower box I cleaned and inspected everything. I cleaned the control panel and all the wires as well.

When I powered up the unit the blower cycled through its 90 second stage. I then put the fan switch at the thermostat to on. The blower started and ran fine. I placed the fan switch to Auto and switched on the heat. The unit fired up, flames were observed but the unit once again shut down in a minute. So I turned the furnace switch to off then turned it to on and it is currently running a full heat cycle. 

Any ideas would really help.


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## Nucon (Dec 8, 2010)

Figured out what the heat exchanger is. Thanks.


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## yuri (Nov 29, 2008)

Read this post and check the temp rise: http://www.diychatroom.com/f17/high-limit-switch-question-88840/


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## Nucon (Dec 8, 2010)

Thanks. I will check the rise temp when the unit tries to come back on. If I understand what this reading might show: Too high a temp = my blower is runnig slow. Then I may have a blower/capacitor failing?


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## yuri (Nov 29, 2008)

Most of the time it is a dirty underside of an AC coil or too small ducts or heat registers closed or dampers closed. Check those first. Only 5% of the time it is a slow running motor/capacitor issue.


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## Nucon (Dec 8, 2010)

ok. I opened all the ducts I had closed from the summer earlier today. I only have two dampers and I visually inspected them. They are fully open. I'll test the rise temp in a bit and post the results.


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## Nucon (Dec 8, 2010)

I notice that after I use the furnace wall switch the blower goes on and the heat cycle will work just fine. But after this heating cycle the next time the blower never comes on. I hear a click, like it tries to start but, it never comes on. Is there a simple way to test the blower motor and capacitor?


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## Heritage Mt. (Dec 9, 2010)

Looking at this my 2cents. If the temperature rise is ok I would look at the static pressure across the coil and between the supply and return. This will rule out any air restrictions.
Is it a new thermostat? What i am looking for is what controls the time off delay for the blower motor, board or stat? It is very rare that a high limit reads to be replaced unless the temp rise was really high from the original installation.


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## Nucon (Dec 8, 2010)

unfortunately, i have been informed that our thermometer is no longer with us. lol

I will have to pick one up tomorrow. I guess its gonna be a cold night. 

Keep the suggestions coming. I'm bound to figure this one out!


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## yuri (Nov 29, 2008)

Metal cooking type stick thermometer is best but you need one with a easy to read scale under 200 degF.


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## Nucon (Dec 8, 2010)

ok. will get one. should I drill a hole in the plenum?


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## Nucon (Dec 8, 2010)

When the Tstat calls for heat I can hear everythign startup. The blower goes on but only for approximately 10 seconds. Then the blower shuts off and shortly thereafter the gas is cut off and the flames go out. Teh entire system turns off and doesnt try restarting.


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## yuri (Nov 29, 2008)

Sounds like the motor is losing power and stopping and then the heat builds up and trips the limit control. Need to run it with the bottom door off and door switch pressed in and check if you get a steady 120 volts on the fan heat terminal to ground. There have been problems with those boards and their solder joints and relays eventually fail on any board. Check and see if the motor is blazing hot when that happens. May be dying and or the capacitor is dying too. Usually that is not an intermittent problem which yours is.
If you REALLY need the heat on soon you may want to call a Carrier or Bryant dealer as this is going to take a couple of days for me/us to talk you thru over the net and order a board etc. I have worked on hundreds of those units. Back tomorrow,Good Luck.


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## Nucon (Dec 8, 2010)

Well, I removed the Fan Limit Switch and the body was quite dirty. I wiped it off and everything seems to be working just fine. I'll be more certain come tomorrow morning.

Thanks to all who helped.


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## Nucon (Dec 8, 2010)

Well it turned out not being the fan limit switch. With the fan coming on and off I was told to bypass the fan and give it constant power. The fan ran as it should have eliminating the motor as suspect. This made the control board suspect as some posters suggested. Sure enough, when I removed the control board I noticed the burned connectors on the back side. I replaced the board and everything works great!

.


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