How does a furnace fan relay work?

Gas Furnaces and Air Handlers use a fan relay to switch the blower motor ON and OFF. The fan circulates the warm or cold air inside the home. Most furnaces and air handlers using a two-speed motor, a high speed for cooling and a lower speed for heating. This setup requires a 6-spade relay.Click to see full answer. Consequently, what controls the fan on a furnace?To put it very simply, the furnace fan limit switch is a control that tells your furnace’s fan when to turn on and off. So, when the furnace isn’t on, it tells the blower not to operate (and send cold air into your home) and when the furnace is on, it tells the blower to turn on and start circulating the warm air.Likewise, how do I know if my limit switch is bad? One common symptom of a malfunctioning limit switch is a blower fan that doesn’t shut off. This happens when the switch simply fails to shut off the fan after the burners have stopped and the air exchanger is sufficiently cool. A bad switch also can prevent a furnace from operating at all. Furthermore, what are the signs of a bad blower motor relay? If you have faulty blower motor resistor you may experience low airflow coming from the vents even when the fan is all the way on high. In some cases bad blower motor resistor may not even turn the blower motor fan as a result your fan will not work at all and there will be no air coming from the vents.Why does the furnace fan stay on all the time?When your thermostat is set to AUTO, your furnace fan should blow only when your furnace is in the middle of a heating cycle. But if your fan runs constantly, regardless of whether your furnace is heating, that’s not normal. Your fan limit switch is on “manual override” There’s a shorted thermostat wire.