Bryant 90 plus limit switch keeps resetting

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Old 01-30-13, 05:53 PM
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Bryant 90 plus limit switch keeps resetting

I have a Bryant gas furnace that keeps resetting the limit switch. When this happens my thermastat reads -AC and begins making a clicking sound. If I shut of main furnace switch ,reset limit switch, turn thermostat back on to auto everything starts up and works fine for up to an hour and then does same thing again.Desperate for any advice!
 
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Old 01-30-13, 06:12 PM
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you have an air flow issue. Check your filter, make sure all registers (supply and return) are open and not blocked.
 
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Old 01-31-13, 11:54 AM
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How do you know the limit switch is opening?

Usually when a limit switch opens, it merely shuts off the burners and causes the furnace fan that circulates air around the house to continue to run.

After the fan reduces the heat enough, the limit switch closes, the ignition sequence lights the burners again and the furnace operates until it overheats again.

You seems to have other drama going on, so I wonder if it's not, in fact, a limit switch issue.


Frankly, the thermostat has NO WAY to know if the furnace limit switch has opened.
 
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Old 01-31-13, 04:43 PM
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SP, on carrier/bryant/payne systems they often use thermostats that require 24V from the furnace. As I have seen many times on the type of thermostat the OP has when the limit opens on a Carrier/bryant/payne system it actually opens R to the thermostat and there by shuts off the power to the thermostat IE the -AC display on the OP's thermostat.
 
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Old 02-01-13, 02:02 PM
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Hello HVAC Tech,


Well, yes, but strictly speaking the thermostat doesn't know if the limit switch has opened. It's detecting a lack of voltage from the furnace, which might have several possible explanations.

I've found the description of what is happening to be confusing to understand.
 
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