# Comfortmaker Furnace Flashing Code 4 when the Main Blower Runs



## beenthere (Oct 11, 2008)

Could be a dirty air filter, or dirty A/C coil. Check if the limit switch is opening.


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## supers05 (May 23, 2015)

Please don't jump out any safeties. Use a meter instead.

Cheers!


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## hotrod45 (Dec 14, 2016)

How do you test the Roll/In Out switch. Is it a resistance test? Could the flame sensor be dirty and causing this condition?

Thanks


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## roughneck (Nov 28, 2014)

Test safety's by measuring across the switch during operation to see if they are opening.


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## hotrod45 (Dec 14, 2016)

Could you please clarify. Do I test the safety devices with the wires hooked up to them and using a volt meter to measure across them when the furnace is in operation? Or do I disconnect the wires from the safeties and do a resistance test across them when the furnace is operating?

Could the flame sensor cause the flame to cut out when the blower cuts in? Does this have to be cleaned on these furnaces.


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## carmon (May 8, 2010)

check with power on..... an open switch will show around 24-26 volts... closed will be zero...... -40.... id be calling a repair man..... keep warm


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## how (Feb 26, 2011)

I am wondering why you are zeroing in on the roll out switch as the problem over the limit switch or switches? 
Are both listed on your legend under the same 4 code led fault? 

You'd test out the limit switch the same way as has been suggested for the roll out switch.


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## hotrod45 (Dec 14, 2016)

Thanks. The code 4 is for both the Roll in/Out switch and the limit switch. The furnace does still run and even at the 30 second intervals it is still about 69 degrees in here which isn't too bad. 

Does anyone know if the flame sensor should be cleaned on this furnace and if it could cause the problem I am having?


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## roughneck (Nov 28, 2014)

If it's giving a rollout/limit error then the flame rod has nothing to do with it. If the limit is tripping then it will not be long until it fails or causes damage to the unit. If the rollout is repeatedly tripping then that's a fire hazard. Neither is designed to be a constantly cycled operating control.


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## hotrod45 (Dec 14, 2016)

Thanks for everyone's help. I tested the Rollout switch and it showed 0 volts when the burner went out. I then tested the limit switch and it showed 0 volts initially as the burner was on but immediately went to 26 volts when the burners cut out. 

I assume I have a faulty limit switch and will obtain one to replace it. Does everyone agree with this diagnosis. A couple of times today the furnace ran normally so this makes the limit switch even more suspect.


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## beenthere (Oct 11, 2008)

That would make it the limit that is opening. But your air flow is probably low and causing it. So correct the low air flow also. You may still need to change out the limit.


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## hotrod45 (Dec 14, 2016)

Thanks. The airflow from the main blower is very strong when the furnace does run. I also checked the airflow from the exhaust fan at the discharge outside and it is strong also. I will change the limit switch and see what happens.


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## beenthere (Oct 11, 2008)

Strong air flow, is a sign of low air flow for the system. Is it blowing out warm, or fairly hot air.


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## hotrod45 (Dec 14, 2016)

The main blower blows warn air when the furnace is in operation. The exhaust fan also blows warm air to the atmosphere.


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## how (Feb 26, 2011)

Dirty air filter? Dirty AC coil? Too many heat outlets turned down or restricted with individual heat outlet filters ? Furniture or curtains limiting the return air grill? Dirt impacted blower wheel? Sound proofing coming loose in the blower compartment? Faulty blower motor run capacitor? Dying blower motor? Faulty limit control? Exchanger crack developing near the limit control? Over gassing from a faulting gas reg or gas valve 
are some of the causes for a tripping limit control.
Half of these you can assess yourself visually without needing any special equipment.

If none of those causes are found, google how to do a "temp rise" furnace test with a simple thermometer. Those test results, when compared to the temp rise listed on your furnace rating plate, will indicate if your furnace is actually overheating or not.
From there we can better direct your next move.


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