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Old 01-30-2020, 08:09 PM   #1
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Bryant plus 80t furnace power issue?


Hello I'm new here and just looking for some advice on my furnaces behavior. My furnace just recently started acting funny about a week ago and it started with the furnace not being able to warm the house up to 60 degrees without acting like it was struggling and eventually shuting down at about 56 degrees and then it comes back on and runs for a minute and it shuts everything down besides the blower and it will stay running until the system cools down, I also get a code 33 before the system shuts completely down and loses total power. The power will shut down and will not come back on regardless of how many times I reset the furnace or how many times I try to reset the main breaker, it will eventually come back on by its self after an hour or two. I have changed the filter, i removed the entire blower and cleaned it, removed flame sensor and cleaned soot. Nothing I have done has fixed it and I could really use some guidance. Thank you all
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Old 01-30-2020, 08:54 PM   #2
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Re: Bryant plus 80t furnace power issue?


How do you know it's losing power completely vs locking out? If a limit is opening, after a certain number of times, furnace will lock out to protect itself.

What's the full model number?
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Old 01-30-2020, 09:05 PM   #3
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Originally Posted by user_12345a View Post
How do you know it's losing power completely vs locking out?

What's the full model number?
I just assume it loses complete power because the furnace power indicator light goes out. The model is 312aav/jav
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Old 01-30-2020, 09:15 PM   #4
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Re: Bryant plus 80t furnace power issue?


So it's a limit switch error. You aren't manually resetting any safety, right?

Cycling on limit can go unnoticed unless it happens enough times during one cycle or it starts not resetting.

You can verify it's the high limit with a meter - do you have one and know how to use it?

Furnace overheating caused by low airflow or being over-fired.

Check your air filter and blower wheel for excessive dirt.

Make sure none of the vents are blocked.

If you have a digital stem thermometer, measure the temperature difference between supply and return near the furnace after 10 minutes of operation.

https://structuretech1.com/diy-furnace-test/

Edit: being a 2-stage furnace, needs to be checked on high fire. 16 minute delay or if u have a 2-stage stat (W2 terminal on board has wire connected), raise the temp a few degrees above the setting.
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I am not in the business of any trade I give advice on. I have non-professional hvac experience + good knowledge of theory. Attempt repairs at your own risk. Never jump out safeties - especially pressure switches - on a furnace for testing with fuel supply on; use a meter. Do not troubleshoot with live line voltage present unless there's no alternative.

Last edited by user_12345a; 01-30-2020 at 09:17 PM.
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Old 01-30-2020, 09:49 PM   #5
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Quote:
Originally Posted by user_12345a View Post
So it's a limit switch error. You aren't manually resetting any safety, right?

Cycling on limit can go unnoticed unless it happens enough times during one cycle or it starts not resetting.

You can verify it's the high limit with a meter - do you have one and know how to use it?

Furnace overheating caused by low airflow or being over-fired.

Check your air filter and blower wheel for excessive dirt.

Make sure none of the vents are blocked.

If you have a digital stem thermometer, measure the temperature difference between supply and return near the furnace after 10 minutes of operation.

https://structuretech1.com/diy-furnace-test/

Edit: being a 2-stage furnace, needs to be checked on high fire. 16 minute delay or if u have a 2-stage stat (W2 terminal on board has wire connected), raise the temp a few degrees above the setting.
The limit switch on my furnace dont appear to have anyway to reset it. It always resets by its self. I do have a multi meter and I'm kinda familiar with using it. I have a laser temperature tool as well. I changed my air filter to a less restrictive one and I also blew what little dust out of the blower. The furnace was pretty clean. I can do that multi meter test but it will have to be early tomorrow, I would do it now but due to Indiana's cold weather me and the wife had to stay in a cheap motel just to keep warm until I can fix this thing
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Old 01-30-2020, 10:01 PM   #6
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Re: Bryant plus 80t furnace power issue?


Monitor voltage drop across the main high limit and see if it goes up to 24v and stays there until it starts working again.

There may be a limit on the exhaust - need to verify it's the main limit, not another one.

It's not the rollout - that's manual reset.

The blower should be running continuously with an open limit circuit.

Those laser thermometers are worthless for testing air temperature.
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Old 01-30-2020, 10:24 PM   #7
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Originally Posted by user_12345a View Post
Monitor voltage drop across the main high limit and see if it goes up to 24v and stays there until it starts working again.

There may be a limit on the exhaust - need to verify it's the main limit, not another one.

It's not the rollout - that's manual reset.

The blower should be running continuously with an open limit circuit.

Those laser thermometers are worthless for testing air temperature.
I appreciate you writing back so quickly. I will get a reading on that limit switch tomorrow and report back here
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Old 01-31-2020, 01:38 PM   #8
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Quote:
Originally Posted by user_12345a View Post
Monitor voltage drop across the main high limit and see if it goes up to 24v and stays there until it starts working again.

There may be a limit on the exhaust - need to verify it's the main limit, not another one.

It's not the rollout - that's manual reset.

The blower should be running continuously with an open limit circuit.

Those laser thermometers are worthless for testing air temperature.
Ok so this morning I got to test it. I turned off the furnace and unhooked the wires from the limit switch and test on ohms and it got a reading of 01.5 to 02.0 it bounces. The limit switch had reset so everything is working for the momment. I had the multi meter set to 20 ohms.
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Old 01-31-2020, 02:22 PM   #9
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Re: Bryant plus 80t furnace power issue?


Let us start in the beginning.

Does the furnace lose total power. Meaning there is no red led error code lights flashing or on at all?

If that is happening then your power supply to it may be failing ( you don't have 120 volts ).

That led lights should always be on showing normal operation or a fault code.

If your door switch on the fan door is weak and not closing it may not be getting power to the circuit board. That is rare but you could try bypass it temporarily if you can connect the wires.

Also check or replace the power switch if it is a simple light switch as they can fail with age. I get a few of those every winter.

Post a pic of the circuit board. There were a batch of them that had faulty solder connections on them at the back and it may be failing and showing no led lights.
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Old 02-01-2020, 02:16 PM   #10
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Let us start in the beginning.

Does the furnace lose total power. Meaning there is no red led error code lights flashing or on at all?

If that is happening then your power supply to it may be failing ( you don't have 120 volts ).

That led lights should always be on showing normal operation or a fault code.

If your door switch on the fan door is weak and not closing it may not be getting power to the circuit board. That is rare but you could try bypass it temporarily if you can connect the wires.

Also check or replace the power switch if it is a simple light switch as they can fail with age. I get a few of those every winter.

Post a pic of the circuit board. There were a batch of them that had faulty solder connections on them at the back and it may be failing and showing no led lights.
The furnace does loose total power sometimes according to the indicator light, it usually will act up if I attempt to heat my house for long periods so for example I keep my furnace on 56 degrees but if I decide to heat the place up to 65 degrees the furnace will start blinking code 33 and it will kick the furnace off before it reaches actual set temperature and sometimes it will completely lose power but it will power itself up usually by its self randomly so it could be anywhere from 30 minutes to 2 hours. The furnace is clean and has a new filter. I have checked every capacitor on the board for bulging and everything looks good. It puts out good heat and the air intake really sucks good air. Could a new chimeny cap cause this?
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Old 02-01-2020, 02:20 PM   #11
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The furnace maintains well as long as I keep it low like 56 degrees, if it's high 60s the furnace seems to have a struggle which possibly leads to the 30 minute to 2 hour furnace shut down
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Old 02-01-2020, 02:37 PM   #12
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Re: Bryant plus 80t furnace power issue?


I suspect the extra long running time is building up excess heat in the heat exchanger and furnace cabinet. That can cause it to eventually trip the limit control.

Strange part is the loss of the LED lights which should never happen.

I suspect your circuit board is dying and having a intermittent problem. It may be due to heating due to the long run times as that seems to be the common factor.

That is a older furnace and the average life of some of those boards is 10-15 years. They can look normal but have intermittent problems.

Make sure you have at least 110 volts to the furnace. If lower then that can be a problem.
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Old 02-01-2020, 05:04 PM   #13
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Just wanted to add that something strange happend early today. So the furnace completely lost power and the weird part is that it turned the power off to my living room as well. The living room and furnace are on separate 20 amp breakers. It's also weird because the two breakers were not tripped and no mater how many times I flipped them they still had no power but after about an hour the power restored it's self and the living room and furnace started to get power. Hmmm could it be a electrical box issue?
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Old 02-01-2020, 08:54 PM   #14
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Re: Bryant plus 80t furnace power issue?


Could be a problem with the main breaker, or at the transformer that feeds your house.
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Old 02-01-2020, 09:18 PM   #15
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Re: Bryant plus 80t furnace power issue?


Issues with the neutral and cause odd problems.
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