nordyne cmf 80 problem

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My furnace seems to work fine except for the fact that the electronic ignitor kicks on and off before and during blower motor is running. I replaced the ignitor and the control module box. Any help with this?
Also, the fan limiter switch has a round dial with three little set prongs..numbers listed on it have 50...100....150, the fan stays on for 3mins after burner is off and starts to blow cold air, is there a setting which the three prongs should be at?
Lastly, what is the purpose of the aux limit switch mounted next to the blower motor?

The info I wrote down is nordyne cmf80-pg-di-n.

THANK YOU for any help.

Makachana

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Your furnace could be in the purge mode or you do not have the correct air flow and the unit is going off and on because of a safety control. You could also have a intermittent centrifugal switch in the combustion air blower. If the combustion air is being taken from under the home make sure nothing has partially restricted or pluged up the intake.

Fan limiter blower switch is supposed to turn the fan on when there is enough heat in the heat exchanger and off after all the heat is blown out of the heat exchanger. The actual setting of this control was made at the factory.If you change it you better have a way to test for the proper temps in your heat exchanger. The control is designed to keep a balance between the heat exchanger over heating and the flow of heat out of your furnace.

Aux limit switch is there as a safety of last resort. If all else fails the aux limit will shut down the burner to prevent any disasters. This is an important switch.

MAKE sure all registers are open in the home and all return airs are open and not blocked. Also make sure you have a clean air filter installed.

hvac1000