Views: 3 Author: Site Editor Publish Time: 2020-07-24 Origin: Site
Damaged condenser fan motors are a common problem with HVAC units; they are exposed to the weather throughout the year and need to be constantly turned on and off to blow air away from the condenser.
When they go bad, they usually freeze after the bearing gets stuck, or they draw the wrong amount of current and stop working.
The condenser fan motor is responsible for pulling air out of the unit, pulling it out of the condenser fins, just like a fan and radiator in a car or truck. On hot summer days, it cools the refrigerant flowing inside by removing heat from the condenser through fins.
When the condenser fan motor often goes bad, the HVAC unit will initially work and then stop. For example, on a hot summer day, when a unit is turned on, it blows cold air first, then stops for a short time and blows room temperature air.
An easy way to tell if a unit has a bad condenser fan motor is to turn on the unit and stand next to the condenser. At some point the fan should start and blow air. Fans don't run continuously only when needed, but if 20 minutes or more have passed and they don't start, there's likely a problem.
When the fan motor isn't spinning, a small stick can be used to touch the blades and nudge them, sometimes making it run again, but it will soon stop. If the motor doesn't spin at all, most likely the bearing is bad and the motor needs to be replaced.
Be careful when using the fan motor, the blades turn at high RPM and can cause injury. Never put your arms, fingers or any body part in the path of the blade. Also, make sure the power to the HVAC unit is turned off before removing the condensing fan motor. A bad motor can suddenly start working again, and if it's not bolted into place, it can get out of control and cause damage. The same thing happens if a new motor is installed, or the problem is fixed and power is applied.
Always be aware that the fan may be fine, the problem may be something else, such as a bad connection, a blown fuse, a bad contactor or start-run capacitor. These need to be checked to make sure the fan motor is bad. Multiple failures can occur simultaneously in a unit, especially as a unit ages.
Checking the fuse or circuit breaker should be the first thing. If the device is disconnected, make sure it is plugged in properly. Opening the side panel and checking the voltage is usually the quickest way to make sure the device is powered on. Most units use 240 volts, which can be verified by looking at the nameplate on the HVAC unit.
Contactors can become pitted and dirty during use, and can develop resistance or open circuits. When this happens, the fan motor will not turn on.
The thermostat engages a contactor that allows high voltage to enter the unit that powers it.
If no power goes into a unit, the resistance can be checked from side to side with a meter, if the resistance is high then it should be replaced as the resistance of the contactor should be very low.
Start-run capacitors are usually combined into one capacitor, called a dual-run capacitor with three leads, but can be split into two separate capacitors.
The start capacitor provides the fan motor with the torque it needs to start spinning and then stop; the run capacitor continues to provide additional torque to the motor when needed.
If the starting capacitor fails, the motor will most likely not start. If the run capacitor fails, the motor can start, but the run current will be higher than normal, causing the motor to heat up and reduce life expectancy.
After replacing a damaged condensing fan motor, a new start-run capacitor should always be installed.
Dual run capacitors have three connections HERM, FAN and COM.
HERM: Connect to hermetic compressor.
FAN: Connect the condenser fan motor.
COM: Connect the contactor to supply power to the capacitor.
If the unit has two capacitors, one is the run capacitor and the other is the start capacitor. One for HERM (compressor) and one for FAN (fan motor) connection.
TIP: It's a good idea to take a photo before you start, or take a note and note down the wire connections and wire colors for future reference.