Limit switch for Lennox G26Q2-50-4


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Old 11-27-14, 10:20 PM
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Limit switch for Lennox G26Q2-50-4

I am looking to replace the limit switch on my furnace because it has tripped 3 times in the last month.

I was wondering if I could just put a generic limit switch or does it have to be this specific one? And where could I look to purchase it locally in Ontario, Canada.

I pulled it out and snapped a couple shots of the switch.

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Thanks
 
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Old 11-28-14, 07:53 AM
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Could be the furnace is having a problem. I would test the switch before you order a new one.
 
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Old 11-28-14, 10:24 AM
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Make sure that it's getting proper airflow before you do that - check the temperature rise (search that term for instructions), change the filter, make sure all vents are open.

If u need a new limit, ideally it should be a direct lennox replacement.
 
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Old 11-28-14, 01:34 PM
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It is FAR more likely that the furnace is overheating than that you have a bad limit switch.

You have an automatic reset limit switch, which means that the switch should open and shut off the burners whenever it reaches it's maximum temperature, which is 205 degrees (the L205) the furnace should go through the ignition sequence an light the burners again when the temperature has been reduced 30 degree Fahrenheit (the -30F).


When limit switches go bad, they usually go bad because the switch doesn't close properly to turn the burners back on again after the furnace has colled off below the set point (205-30= 175 )

So if you are finding the furnace cool with the thermostat calling for heat and the limit switch open (24 VAC on only one side) that would mean that the limit switch should be replaced.

It would still mean that the furnace is overheating in the first place though, and you need to identify what is causing that problem.
 
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Old 11-28-14, 02:04 PM
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Thank you for your replies. I found that after limit switch opens and the burners turn off the furnace starts blowing cold air. It blew cold air for 2-3 hours and I thought that should be enough to cool the limit switch back to closed.

So if I understand this correctly the temp needs to get to 30F which is below freezing temp to get the limit switch to close again? How would it ever be possible to achieve that temp inside the house?

I apologize my understanding of HVAC is limited. Thanks for the help everyone.
 
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Old 11-28-14, 02:14 PM
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>


No. As encoded on the limit switch, the switch should open at 205 degrees Fahrenheit and should close when it's cooled 30 degrees below that temperature (175 degrees)

Since the switch isn't closing relaibly after it cools, you are correct that it should be replaced.

But don't forget you need to identify the underlying problem that is causing it to open in the first place.

If you turn the thermostat way up so that the burner runs constantly, you will probably cause the limit switch to open if something is impairing the air flow through the furnace. The furnace burners should be able to run constantly without the furnace overheating.
 
 

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