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Old 12-11-2019, 07:53 PM   #1
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Bryant 80T Furnace Cool Down Issue


General question, I think! If I try to increase the thermostat heating temp while the furnace is in its cool down stage and not fully shut off, the system will not sense the change, continue to cool down and does not come back on at all. I then go downstairs, power the unit off for 10 seconds, turn power back on, and everything returns to normal. It has been doing this for 3 years now, so I make sure that I control the heat setting manually to ensure I don't encounter that scenerio when it is on automatic control.

Seems like some logic error, but I just can't find anything that would provide an answer as to what is going on. Any ideas?
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Old 12-11-2019, 08:02 PM   #2
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Re: Bryant 80T Furnace Cool Down Issue


It's normal for it to complete the cool down cycle before starting up again with a new call for heat. But after that it shouldn't just sit there.

If you wait 5-10 minutes before turning up the temp and triggering the heat again, does it respond normally?

it's not necessary to short cycle the furnace -> leave the stat alone and let it do it's thing, it should be off for at least 5 minutes at a time.
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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.
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Old 01-31-2020, 05:07 PM   #3
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Re: Bryant 80T Furnace Cool Down Issue


Thanks for getting back to me!

Once I try to set the temperature during cooldown, it will shut off normally, and then will never come back on. Once it gets cold in the house, then I know it needs to be short cycled. I control it manually and make sure I time it correctly when I adjust the temp.
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Old 01-31-2020, 05:09 PM   #4
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Re: Hello from Michigan - Bryant 80T Question


Welcome to the forums. Post the question over in the HVAC section too.
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Old 01-31-2020, 05:17 PM   #5
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Re: Hello from Michigan - Bryant 80T Question


What is cool down mode? Is there a flashing code that you can see?

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Old 01-31-2020, 05:35 PM   #6
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Re: Bryant 80T Furnace Cool Down Issue


Does the stat call for heat when the temp drops below the setting?
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Last edited by user_12345a; 01-31-2020 at 05:47 PM.
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Old 01-31-2020, 09:05 PM   #7
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Re: Hello from Michigan - Bryant 80T Question


Welcome to the site
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Old 01-31-2020, 09:07 PM   #8
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Re: Bryant 80T Furnace Cool Down Issue


Check for a call for heating with your meter to see if the thermostat is calling, as stated above.
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Old 02-01-2020, 05:20 AM   #9
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Re: Bryant 80T Furnace Cool Down Issue


Check your air filter, it may be dirty and causing your furnace to lock out on a high limit error.
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Old 02-01-2020, 06:50 AM   #10
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Re: Bryant 80T Furnace Cool Down Issue


Hi! Thanks for the input.

During the cool down period, the thermostat light will go from a bright red to a dimmer (ie. call for heat?) one with the blower still working. It will then shut down momentarily and then the thermostat will click back on to start the process again until the desired heat is reached. This was the expected norm and is how things here most of the time.

It is just at that time of cool down, when I manually increase the heat that the thermostat clicks (call for heat) like it recognizes the changes but after it first shuts off, never comes on. The same occurs if the stat is on auto and tries to increase the temp during cool down in the morning.....result...no heat.....very cool morning!

I replaced the air filter with no change. It really operates just fine until this particular combination of events occurs.

That's why I keep leaning to a bad logic component of some sort in the electrical switching portion that I think is in furnaces. Something like an AND gate where one leg carries the cool down signal, the other, the stat, (if both on, then it gets set for next cycle)? Hope this makes sense..... I am going to look at a schematic, if I can find one, and trace out the circuitry.

Any other ideas are greatly appreciated!
Note- this furnace was most likely behaving this way before we bought the house in the Spring. (AC behaves fine). Going on 3rd year

Thanks!
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Old 02-01-2020, 07:04 AM   #11
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Re: Bryant 80T Furnace Cool Down Issue


There is no “cool down signal”. The thermostat calls for heat or it doesn’t.
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Old 02-07-2020, 12:50 PM   #12
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Re: Bryant 80T Furnace Cool Down Issue


I am a novice, but trying hard to get up to steam....

When the thermostat light goes from red to off, I am assuming it is telling the furnace to shut down once it cools down sufficiently first. It is at this time, if I increase the temp manually from the thermostat(red light goes on), that the furnace never comes back on after it fully shuts down. It behaves this way in automatic, but only occurs if it tries to increase the temperature during this shutdown period.

Hope this helps. It is a really odd behavior.
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Old 02-07-2020, 04:04 PM   #13
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Re: Bryant 80T Furnace Cool Down Issue


Brand and model number of thermostat.
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Old 02-07-2020, 04:45 PM   #14
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Re: Bryant 80T Furnace Cool Down Issue


White Rodgers - Digital Comfort II - do not see model number
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Old 02-07-2020, 04:50 PM   #15
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Re: Bryant 80T Furnace Cool Down Issue


Fairly old thermostat. Might be a thermostat problem, not a furnace problem.
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