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Every home is different. In your HVAC career, you’re likely to encounter AC systems ranging from the very old to the factory new. Consequently, you need to understand the different types of motors you’ll encounter and how to properly handle and replace each one as needed. Take some time to familiarize yourself with the 3 motors you’re most likely to encounter:
Since a condenser fan motor will get rained on and be exposed to the elements, it’s rated for use outdoors sealed up on the ends and sides to keep water out. These motors are usually one speed and come in horsepower ranges from 1/6 hp to 1/3 hp. They always have a capacitor, usually a dual capacitor if it’s an original motor and a single capacitor if it’s a replacement aftermarket motor. The factory motor usually has three wires and the aftermarket version usually has 4 wires.
The main thing to remember on a condenser fan motor is the main service issue is usually a bad capacitor. This issue generally surfaces during summer, when the weather is hottest. If the motor is bad, measure the fan blade height to the finger guard before you ever remove it. The placement of the blade is absolutely paramount to the operation of the condenser, even more so than its original placement on the motor shaft. Consequently, you should always keep any replacement fan blades at the exact same height, since getting this blade height wrong by even an inch can mean the compressor will overheat and burn out. If you need to replace the condenser fan motor and capacitor, take note of these key pieces of information first:
RPM
Frame size
HP
Voltage
Above all, never try to force the replacement blade onto the motor. After all, a motor is easy to replace while the correct fan blade might take you weeks to find.
Finally, don’t fall back on the assumption that you can simply substitute a different pitch blade when necessary. The wrong size or type will not work and may overheat the fan motor or simply not move enough air, meaning that the AC unit won’t do its job. Airflow at the condenser is critical.
Another popular air moving AC unit motor is the blower motor. The blower motor looks similar to the condenser fan motor, except the blower is ventilated on the sides and/or the ends to allow air to pass through. Blower motors also have a capacitor, in addition to way more wires than condenser fan motors.
The main cause for blower motors failing is that dirty air passed over them and stopped up the vent hole, causing the motor to overheat. This indicates a deeper problem since the air filter should catch dirt before it reaches the motor. Sometimes a blower motor experiences a capacitor failure, causing it to turn backward. They look normal running this way but move almost no air. After a couple of hours, the evaporator coil freezes and the house overheats, prompting the homeowner to call for help.
To replace a bad blower motor, remove the blower housing with the motor and blower. You have to remove the curved plate first, but this is where the wheel slides out of the housing. Make sure to reattach the blower wheel securely when you’re done to avoid burning out your new motor. Finally, remember that blower motors also have universal replacements. Just remember that electric heat furnaces us 230-volt blower motors (in contrast, gas furnaces use 115-volt motors) and you’re good to go!
The most expensive and hardest to replace of the air conditioning motors is the compressor. This motor is sealed inside the compressor housing, so you can’t determine visually if the motor has failed. The only parts you can test are the three terminals sticking out of it.
Compressor motors are really two motors in one: the start motor and the run motor. They just happen to be connected together at the common wire terminal. The start winding are very small wires that are wound on the motor to deliver a quick burst of power and start the motor. Since the start winding are only designed for the initial spark. if the start winding have to work for more than about three seconds, they’re likely to burn out. The motor’s run capacitor ensures the start winding don’t work too hard and keeps the entire motor running correctly.
While this is an expensive part to misdiagnose (a new compressor can cost up to $1000 wholesale), don’t panic. It’s difficult to correctly diagnose a motor you can’t see, so the majority of problems with compressor motors come from misdiagnosis rather than equipment failure. Using a meter, test each of the three terminal connections to see if they display the proper resistance sums and have any charge to ground. If there is any reading to the ground, the motor is bad.
Be sure to always remove the power and discharge any capacitors in the unit. The compressor might not read anything when you test it–this is when 90% are incorrectly condemned. The truth is that compressors have an internal safety switch that turns the motor off when it overheats, and if you test the motor while the switch is activated, it’s easy to assume the motor has burned out. With this information in mind, never rush to the assumption that the compressor is burned out. Compressors should last the life of the unit. Before you try to replace the motor, try to determine the cause of failure or see if the safety switch eventually deactivates.
Knowing the normal of each common type of HVAC motor is a critical first step in developing your long-term HVAC career. Take the time to familiarize yourself with the most common types of motors and learn how to repair or replace each as necessary. As you build your understanding of air conditioner systems and maintenance, you’ll become better at your job as a technician.
