Home AC units use motors to move the air and motors to move the refrigerant. Whether due to overheating, a lack of proper maintenance, or old age, HVAC motors can break down and cause the entire system to come to a halt. That’s where you as the technician come in! How much do you know about diagnosing and repairing damaged AC motors?
Common Air Conditioning Motors
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 5 motors you’re most likely to encounter:
- Condenser fan motor
- Blower motor
- ECM motor
- Combustion fan motors
- Compressor motors
1) Condenser Fan Motor
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:
- Frame size
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.
2) Blower Motor
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!
3) ECM Motor
The ECM motor is a blower motor with an electronic control module mounted on the end. These motors are special; some must be set up at the supply house with special programming. Others have program modules you can buy to do it yourself. A few particularly advanced models even allow you to program the unit from your phone!
ECM motors can cost up to $1000, so be sure to get current pricing before you give your client a quote. Beginning HVAC technicians may benefit from getting an expert technician’s input on how to handle ECM motor repairs since, considering their high price tag and complicated inner workings, trial and error is not the way to go with ECM motors. When you’re dealing with equipment this expensive and advanced, it’s better to be safe than sorry.
Pro Tip: If you get stuck on an HVAC job and can’t get hold of an expert, call the AC motor’s service number to talk to a brand representative. They’re usually willing to help you out.
4) Combustion Fan Motors
Combustion fan motors are found in gas furnaces. These types of motors don’t have a capacitor, just two wires. It’s very easy to diagnose what’s wrong with a combustion fan motor. If the motor is receiving its full 115 volts but not running, it’s burned out and the whole thing likely needs to be replaced. You can usually buy replacement units from factory brand reps.
Since these motors tend to last as long as the gas furnace they’re installed on, you likely won’t see too many combustion fan motor failures. But even when you do, the replacement won’t take you very long and will be a pretty straightforward process.
5) Compressor Motors
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 windings are very small wires that are wound on the motor to deliver a quick burst of power and start the motor. Since the start windings are only designed for the initial spark. if the start windings have to work for more than about three seconds, they’re likely to burn out. The motor’s run capacitor ensures the start windings 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.
AC Motor Replacement & Repair
Knowing the normals 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.
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Troubleshooting is one of the most important skills you can possess in the HVAC industry. Learning how to apply these problem-solving methods that point you to the issue quickly will not only save you time, but also leave you with happy customers who are sure to call you next time the HVAC system stops working. What do you know about the process of HVAC troubleshooting?
Troubleshooting Common HVAC Problems
All good troubleshooters have a few natural traits in common. In order to exhibit excellent troubleshooting skills yourself, you’ll need to build on your existing knowledge of how an HVAC system should work, narrow down the problem, and communicate with your clients about what you need to do and why. This process is crucial to providing quality services. Let’s break down each component of an HVAC troubleshooting strategy:
- Know the normal
- Eliminate unnecessary work
- Discuss with the customer
1) Know the Normal
Do you know the normal of the system you’re working on? Good troubleshooters learn this first since you can’t identify a problem without knowing what a normal situation is supposed to look like.
For example, imagine you are working on a condenser unit and the unit is running but the compressor is very hot to the touch, far hotter than anything you’re familiar with. So now you are trying to see what is happening to cause this compressor to be operating at this elevated temperature. If you don’t know the normal of the HVAC unit, you’ll end up spending hours testing each potential problem as your customer gets impatient. Train yourself to look for the cause behind abnormal condition so you don’t end up chasing your tail.
In addition to understanding normal functions of an HVAC unit, you should also be familiar with what mechanical parts should be used and why. It’s unfortunately very common for inexperienced technicians to install the wrong parts in a client’s air conditioning system. If you can’t find anything wrong with the system’s functionality, speed, or temperature, yet the client is experiencing problems, check the components. More than likely, at least one is incorrectly installed or the wrong piece altogether.
Pro Tip: During an HVAC service call, if you notice an installed part that didn’t come from the original manufacturer, double-check it. It’s probably the wrong part for the unit in question.
2) Eliminate Unnecessary Work
What can you do to eliminate time-consuming tests as you search for the problem? For example, if a customer tells you their attic HVAC unit isn’t powering on, don’t immediately start disassembling it and hunting for faulty wiring or other problems. Check that the power switch is turned on. While this may seem silly, it’s surprisingly common for stored Christmas decorations or a distracted family member to accidentally flip the switch. This simple solution definitely saves you time!
Additionally, keep yourself informed on the situation before you even arrive on the scene. Talk with your client to get the big picture. Which technician or service company did their HVAC maintenance work in the past? What exactly did they do? If you can, drive past the worksite and observe the unit from the street. Has it been tampered with? Have bushes or weeds grown around it?
Before you begin the job, sit down with the client and discuss any complaints they may have about how their HVAC system works. Additionally, ask them about their home’s work history and any variables that may have contributed to the problem. For instance, if they noticed the AC beginning to falter after they hired someone to mow their lawn, it’s possible that one of the mowers accidentally severed a cord with their machine. This gives you an excellent idea of where to look for the problem.
For an easy reference for both you and the customer, create a flowchart of common HVAC problems and their possible causes. While this isn’t a foolproof method, having the information easily accessible in a chart can help you narrow down the problem quickly. A chart will also give the customer a better idea of what you need to do and why.
3) Discuss with the Customer
Finally, remember that your first priority is customer satisfaction. Once you believe you know what the problem is, discuss your findings with the customer and explain what you need to do, why, and how much it will cost. Don’t save this part till the end! Make sure the customer knows exactly what they’re getting and what they’re paying you to do. This also gives them the option to refuse a certain service if they don’t want it.
This step not only builds trust with the customer, but it also establishes you as an expert on their HVAC system and as an honest contractor. Rather than trying to upsell them on expensive work or equipment they don’t need, you’re trying to restore their comfort level in their home. A satisfied customer will recognize this and happily refer you to their friends!
Your HVAC Troubleshooting Strategy
In the end, remember that operating with an effective HVAC troubleshooting strategy benefits both you and your client. Your client, of course, will be happy with a job that’s both well done and finished quickly. Meanwhile, you’ll have extra time to apply toward other jobs, as well as a satisfied customer who will recommend you to friends and almost certainly call you back for further work. Don’t sell yourself short by neglecting problem-solving knowledge! Practice troubleshooting in an HVAC setting to ensure your future successes.
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Why is it so important to understand what a normal HVAC system looks, sounds, and feels like? Simply put, you must know normal before you can diagnose abnormal. Adopting this philosophy will have a profound impact on how you see and work on almost everything.
No matter what you are doing, if you know what is normal, you will be much more confident in the outcome. Technicians that don’t realize this tend to make many mistakes, incorrect diagnoses, and improper installations. What impact will this have on your HVAC career?
Normal Isn’t Always Good
It should go without saying that normalcy in an HVAC system isn’t always a good thing. For example:
- It’s normal that most a/c systems are installed incorrectly.
- It’s normal for technicians to ignore superheat and subcool when charging or testing a system
Even if being normal isn’t always a good thing, it’s still important to recognize what a normal system looks like. If you know that most systems are installed incorrectly, it will make you look harder and not assume anything. If you know that most technicians ignore proper charging procedures by ignoring superheat and subcooling, you will take a closer look at that even though you may be there for something entirely unrelated to the refrigerant charge.
Sometimes knowing normal is knowing how something reacts when it fails. For example, if a liquid line drier starts to clog up, it’s normal for a temperature drop to be detectable from the inlet to the outlet side. It’s also normal for a clean drier to not have a temperature drop. Both of these are the norm for that particular situation, but both equally important to know.
On the other hand, two seemingly opposite functions could also be normal. For instance, an evaporator coil will produce a large amount of water if the air is high in humidity, and none at all if the weather is dry. If you don’t know the difference, you might misdiagnosis a problem based on incorrect knowledge of what the system is supplied to do. Just the fact the coil does or does not produce water means nothing if you don’t understand the differences.
Pro Tip: Even if you notice fluctuations in certain HVAC functions, don’t assume that means there’s a problem. The system may be designed to handle or cause those changes. Stay informed of real problems to watch for.
“Normals” of HVAC Compressors
How much do you know about the normal functions of HVAC compressors? Let’s just consider the temperature of the shell of the three compressors. The scroll on the top of the compressor should be very hot since that’s where the head discharges into the dome. In fact, the entire dome should be very hot anytime the unit is turned on, while the sides are cooled by suction gases and will not be nearly as hot. Since the reciprocating compressor is also cooled by suction gases, you should only notice heat where the hot gas line leaves the shell.
If a technician touches a rotary and assumes it is overheating because he confuses it with a scroll, they’ll misdiagnose a system issue and perform unnecessary work. Similarly, touching a hot reciprocating compressor and assuming it is operating normally because you don’t know better will allow a potentially severe problem to get worse.
Know What a Normal HVAC System Looks Like
It’s been said that “You must know normal before you can know abnormal”. This saying is particularly true in an industry that deals with troubleshooting. The first step toward identifying a problem is knowing what normal operations should look like and what any deviations from the norm could mean.
Connect with us to learn more about normalcy in the HVAC industry and how to identify common issues.