Furnace Fan On Off Switch

The system uses a temperature probe to detect temperature changes inside the heat exchanger see image below and turns your blower on and off in response.

Furnace fan on off switch.

Most thermostats have a switch for the fan that says either on or auto which means that the fan turns on when the equipment comes on. If you have your thermostat s furnace or air conditioning for that matter fan set to on the fan will continually run regardless if your furnace is running through a heating cycle i e whenever your furnace is actually producing heat. Fan limit switches are used on all types of building heating furnaces. Limit switch issue furnace blower fan wont turn off if the furnace overheats then a limit switch will open.

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The fan limit switch on a heating furnace controls when the furnace blower fan turns on and off. Among other benefits this switch allows you or your plumber or repair technician to shut off the electricity to the furnace without having to go to the main service panel to switch off the circuit breaker. Essentially this means that it determines when the hot air should be blown through your ventilation system. That will cause the burners or heat source to shut off and the fan to run until the limit switch closes again.

This control also provides a safety limit that turns off the burner or furnace if temperatures at the furnace are too high. If you have your furnace again or air conditioning fan set to auto your system s fan will run during the furnace s heating cycle only. Details of checking the thermostat s fan auto off or fan on switch position when the furnace or air conditioning fan won t stop running are at fan wont stop thermostat switch other snafus such as a shorted thermostat wire can also cause the a c or warm air furnace fan to run continuously. Throw the switch to on if the fan comes on then you.

Your furnace fan limit switch is basically a control system that determines when the furnace blower assembly should turn on and off. In some cases the limit switch will stick open and this will cause the fan to run continuously. It s usually mounted on the side of the furnace or a wall nearby.