The blower motor resistor is responsible for controlling the blower motor speed. In the past, this was done by varying the voltage supplied to the blower motor. In newer applications, the blower motor resistor is actually a solid state module that sends a varied signal to the blower motor.
The thermostat is what tells these separate systems to work together. In normal operation, when your thermostat is set to "auto," it will tell the blower fan plus the heating or cooling components to turn on and off at the same time when the desired temperature is reached.
The fan limit switch controls when the furnace blower fan turns on and off. This control also provides a safety limit that turns off the burner or furnace if temperatures at the furnace get too high. Fan/Limit switches are used on all types of heating furnaces.
In short, common issues that can cause an air conditioning unit fan to stop spinning are electrical issues, problems with the capacitor, contactor issues, a burnt out air conditioner motor, a broken fan belt, or clogged air filter.
The blower motor resistor is responsible for controlling the blower motor speed. In the past, this was done by varying the voltage supplied to the blower motor.
A sure sign of a bad AC capacitor is a humming sound from within the access panel. Any humming noises indicate a problem with the air conditioning system or the components of the AC unit. Try turning the power on and off again to see if it was a one-time issue with the motor or a recurring problem.
In most newer systems, the button is often directly next to the blower motor, while in older systems, it may be harder to spot as it is sometimes underneath or behind the motor. The reset button is often made of yellow or red plastic and marked with a large “R ” to make it easier to spot.
The green wire on your thermostat connects to the fan of your furnace or air handler. It connects your thermostat to the air handler or furnace.
It's controlled by the fan control switch and blower motor relay, which are responsible for managing the amount of voltage the blower motor receives, allowing it to function at different speeds.
Blower Motor Resistor Test
Typically, if the fan will work on some speeds but not on others, the resistor is suspect. Okay, let's say there's no melting going on, but your fan doesn't work on all speeds. Typically, if the fan will work on some speeds but not on others, the resistor is suspect.
The short answer: Definitely not. (Unless you have manually engaged your outside fan to run constantly, but it shouldn't be running for hours on it's own.) If your HVAC is functioning correctly, it should keep your house cool by cycling on for 15-20 minutes at a time—with distinct pauses in between each cycle.
If your air handler is running but not blowing air, there are two likely scenarios: either a broken AC blower belt or an issue with the motor itself. If the air handler is humming or buzzing but not making the mechanical sounds of a motor running, you're most likely talking about an issue with the motor itself.
The fan setting on your thermostat controls your HVAC 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.
Thermostat Wiring Tips
The W wire is connected to your heating system. If your thermostat controls your heat, you will have a white wire. The Y wire is yellow and connects to your air conditioning compressor. The G wire is green and connects to the fan.
According to the new motor White = L1 (neutral), Black = High speed, Blue = Medium speed, Red = Low speed. Check the diagram on the old motor, to figure out which wires are which. From what I can see, looks like on the old motor: Black = High speed, Yellow = Medium high, Orange = Medium Low, Red = Low speed.
In AC systems, the air conditioner reset button is on the outside unit's lower edge, typically close to the ground. Some models have the reset button located behind the service panel, which may require tools to remove. Reset buttons are usually red or yellow with a clear “reset” label.
When an HVAC unit is equipped with a PSC (Permanent Split Capacitor) blower fan, a capacitor is required to both start and run the motor. The capacitor's job is to store and then discharge electrical energy in order to create an artificial phase of electricity for the blower motor power supply.
2. Switch is stuck. Another symptom of a bad or failing blower motor switch is a switch that is stuck, or frequently gets stuck. If the switch or any of its contacts becomes damaged, this may cause the switch to jam, or get stuck when you trying to change the setting.
If the start capacitor malfunctions or wears out, it usually prevents the HVAC unit or the blower from turning on. A bad run capacitor won't prevent the unit from starting, but it can lead to the unit shutting down prematurely, overheating or making more noise than usual.
#1 Most Common Air Conditioning Repair – Bad Capacitor
The fan of course makes a whirring noise, the compressor is like a deep buzz like a refrigerator running. Holding your hand above the fan should feel warmer than the outside air.
Since AC capacitors are high-voltage components that might cause significant injury to you even if the power is out, it is strongly recommended against changing them yourself. Follow any instructions provided with your new unit purchase if you're thinking about replacing your own AC capacitor filter.