Motors are an integral part of any HVAC system. Typically, a car can’t move without an engine…in the same way, an air conditioning unit won’t operate correctly without a motor. The motors in an HVAC system are responsible for operating the compressor, pumps, and fans.
Often, motors could break down due to different factors such as old age, improper maintenance, and overheating. When this happens, pretty much everything in the HVAC comes to a standstill, and that’s when a client reaches out looking for technician services. The big question: can you diagnose and repair a failed AC motor?
Types of Motors in HVAC Systems
To perform repairs effectively, efficiently, and quickly, you need to have a good understanding of the commonly used HVAC motors and how to handle each one of them. Here are some of the common types of motors you’re likely to encounter while carrying out repairs and maintenance.
One of the most common HVAC motors is the blower motor. This is how you know if it’s a blower motor: it is connected to a blower fan either on the end of its shaft or through a pulley for air movement. Blower motors come in two types: there’s single-speed and variable-speed motors. The only difference between the two is that the single-speed ones blow air at a constant speed while the variable-speed motors can adjust their speeds and blow air at varying speeds.
When dirty air passes over the blower motors, it might stop the vent hole and consequently cause the motor to overheat. This could also indicate other underlying issues – the air filter should repel the dirt way before reaching the motor. There’s also the issue of capacitor failure.
If you see the blower isn't moving, moving too slow is vibrating, or is just inconsistent, work your way through the system. Check the fan itself for dirt and debris, check the pulley, if necessary, remove the pulley and test the motor on its own. Sometimes the fault is in the motor, sometimes it is the pulley and sometimes it is the blower assembly.
When a blower motor fails, it means that it can’t move any air. If there’s no air movement, it won’t be long before the evaporator coil freezes, causing the system to stop cooling – and that’s when you receive that call!
In case you need to replace the blower, ensure that you remove the motor together with the blower housing. The
With some repairs, the fix is as simple as cleaning out the blower assembly, in others, you may need to do an entire replacement of the motor and blower assembly. Especially with a dirty blower, be sure to take pictures to show your customer what poor maintenance will do to their system!
These types of motors are the hardest and the most costly to replace. Why is that so? It is impossible to visually tell whether the motor has failed because it is usually sealed in a compressor housing. However, with that said, it usually has protruding power terminals that you can test to determine the blower’s condition. Pull off the compressor power plug and test the windings for shorts. Feel the temperature of the compressor housing. Sometimes, the thermal overload switch will kick in, which will result in an open circuit.
Usually, the compressor motor is made up of two motors: the run and start motors. As their names suggest, the start motor provides the initial spark to power and start the motor while the run motor ensures that the entire compressor motor is running properly. These motors are connected using a common wire terminal.
As highlighted earlier, compressor motors are difficult to diagnose, and therefore, most problems arise from the misdiagnosis rather than the failure of the motor itself. If you come across this type of blower motor, the first thing to do is test the charge to the ground and the resistance of the terminals. If you get some reading to the ground, then there’s a problem with the motor.
Also, always make sure that you discharge the unit’s capacitors and remove the power. These blowers have a safety switch that turns off the motor in case there’s some overheating. If you test the system while this switch is activated, you might get the impression that the motor is burned out, which might not be the case. Don’t rush to replace the compressor motor; instead, carry out different tests to see if the switch deactivates.
Condenser Fan Motors
Another common motor is the one-speed condenser fan motor that has a horsepower of about 1/6 to 1/3hp. The motor comes fitted with two capacitors (original motor), with the replacement aftermarket versions having a single capacitor (the two have three and four wires, respectively).
Most issues with the condenser fan motor are capacitor-related, especially during the hot days of summer. Before replacing the capacitor and the motor, make sure you determine its voltage, hp, RPM, and frame size.
If you also need to replace the fan blades, ensure you get the exact same height…if you get it wrong, the compressor will overheat and probably burn out.
Combustion Fan Motors
These types of motors are common in gas furnaces. Unlike the above three types, the combustion fans don’t use capacitors; instead, they have two wires. The motors are pretty much straightforward, and their diagnosis is relatively easy.
If the motor is not running (while receiving the recommended 115 volts), it is burned out and probably requires replacement.