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FAN-ON: the middle setting on the fan limit switch dial (green arrow) is the “FAN ON” temperature. Ths setting turns the blower fan ON when supply temperature is rising, and is usually set around 130 °F. This switch is usually factory-set at 200 °F.
What controls the fan on a furnace?
A fan limit switch is a component of a furnace system that determines when the furnace blower assembly for hot air turns on and off. Essentially, this means that it determines when the hot air should be blown through your ventilation system. The fan limit switch also has two other functions.
Does the fan turn on when the heat is on?
There are two settings on your thermostat to control the fan – auto or on. AUTO means that the fan turns on automatically only when your system is heating or cooling air. Once the thermostat reaches the desired temperature, the entire system shuts off until the next cycle.
What turns the circulation blower on when the furnace reaches temperature?
A probe inside the switch monitors the temperature of the burner assembly to turn the fan on once the burners are hot and turns the fan off once the burners cool down (when the thermostat stops calling for heat).
What device turns on blower motor during the cooling cycle?
In a heating and cooling system, a control relay that energizes a blower motor during the cooling cycle. Many systems use a two-speed blower motor that the blower relay runs in high speed for cooling and low speed for heat.
How do you reset the fan limit on a furnace?
How to Reset a Furnace Limit Switch Locate your furnace’s heating duct. Locate the white limit switch. Look at each arm to identify the settings. Identify the component (setting) located in between the two arms. Set the temperature on the middle component to approximately 105 to 115 degrees Fahrenheit.
What is difference between fan on and circulate?
When the heat is on, the fan will only turn on as your home heats up. When cooling, the fan will only run while your air conditioner is running. Some thermostats now offer a “Circulate” setting that will turn your fan on for a set period of time to help in circulating the air.
What is the fan for on thermostat?
The fan setting on your thermostat controls your HVAC’s system blower. The blower helps circulate hot or cold air throughout your home until the temperature on the thermostat is reached. There are two settings on your thermostat to control the fan – auto or on.
What does the fan do on a heat pump?
The function of the fan in heat pumps is to facilitate airflow and circulation. It blows air to distribute warm or cold air in the room. You can switch the fan “on” at the onset for a few minutes after turning on the heat pump to accelerate the distribution of cold or warm air in the room.
Why does my furnace fan keep turning on and off during heat cycle?
you most likely have a bad fan limit switch. Your furnace fan limit switch is basically a control system that determines when the furnace blower assembly should turn on and off. So if your furnace blower is turning on and off when the furnace isn’t in a heat cycle, it usually means the fan limit switch is defective.
Why does my furnace fan turn on by itself?
If your fan limit switch is set to AUTO but the fan continues to run without ever stopping, you’ll need to call a professional. Two problems that could cause your fan to run without stopping include: A bad fan limit switch that needs to be replaced. Bad thermostat wiring.
Why does my heater fan keep turning on and off?
If your furnace keeps shutting off, it could be due to low airflow. There are several indirect issues that cause low airflow. Dirty Air Filters. If you don’t change your air filters often enough, the filters will become dirty and clogged, which means the heat exchanger retains heat and eventually causes it to overheat.
What is an inducer fan?
A draft inducer is a fan that’s located inside of your furnace near the heat exchanger. By turning on before your furnace ignites its burners, the draft inducer is able to clear out any combustion gases that might be lingering in the heat exchanger from the previous heating cycle.
What does pressure switch do?
A pressure switch is a device that operates an electrical contact when a preset fluid pressure is reached. The switch makes an electrical contact on either pressure rise or pressure fall from a certain preset pressure level.
How do I control the temperature of my furnace?
Achieving optimum temperature control Optimum temperature control is achieved using an independent furnace sensor. The heat control output can either be connected to gas burners or thyristors. In some applications a cooling output may also be connected to a circulation fan or an exhaust damper.
How do I know if my limit switch is bad?
The most common sign of a malfunctioning limit switch is the continuous operation of your furnace’s blower. Just as the limit switch won’t allow the fan to turn on until the warm air has reached the right temperature, the limit switch also shuts down when the air cools to a certain temperature.
