Residential HVAC systems and light commercial units primarily use one type of motor. But there are a few different types of motors worth knowing about. Below is a list of some of the most common types of HVAC motors.
PSC (Permanent Split Capacitor)
Medium torque, single-phase motor with run capacitor always in the circuit. Has a cage rotor and a stator with two windings, known as main and auxiliary windings. This type of motor is the most commonly used in HVACs and includes condenser fan motors, blower motors, and compressor motors.
CSCR (Capacitor Start, Capacitor Run)
Higher starting torque, two-phase motor with both a start and run capacitor. Starting capacitor is removed from the circuit after the run capacitor kicks in, using potential, current, or centrifugal relay. Also has a cage rotor with main and auxiliary windings.
CSIR (Capacitor Start, Induction Run)
Less common, this motor’s capacitor start has a cage rotor with main and auxiliary windings placed 90° apart. However, there is no run capacitor.
Three-Phase Induction Motor
Motor with low starting torque that uses a rotating magnetic field produced by three-phase currents. Doesn’t require capacitors.
Direct Current Motor
Utilizes direct current. Commonly uses brushes to transfer an electrical charge to the armature (rotor) of the motor.
ECM (Electronically Commutated Motor)
Increased efficiency range motor that relies on a microprocessor controller to generate electrical current. Requires no brushes, thereby reducing the amount of physical contact. Similar to the three-phase, it depends on a rotating magnetic field. ECM motors are used in variable-speed blowers to give users more control. However, these are not the same type of blowers as multi-speed blowers.
Multi-Speed vs. Variable Speed Blowers
Traditionally, HVAC systems worked with a single-stage furnace blower that registered a specific temperature and turned on or off whenever that temperature was achieved or changed. But this created pockets of hot or cool air instead of a steady temperature across the entire unit. It also uses energy similar to the way that opening a fridge does. The longer the fridge door remains open, the warmer the air inside the fridge becomes. Once the door is closed again, the motor has to work harder to return the temperature back to its cooler state again. The harder the motor works, the more energy it has to use up.
Unlike the traditional systems, multi-speed blowers have a control for both cooling and heating to ensure that an area maintains a steady temperature throughout the day. This type of technology has been improved through the use of an ECM.
A variable-speed blower utilizes an ECM to create a continuous blow that maintains close to an exact temperature. This continuous blow can improve the air quality of your home by ensuring constant filtration.
The Benefits of ECMs
While the other motors discussed in this article depend on mechanics (physics, mostly) to control their functions, ECMs rely on a microprocessor that gains information from a closed feedback loop. This means more precise operations and increased motor control. For example, in variable-speed blowers that rely on programmed air flow, the motor may speed up when something causes a reduction in that air flow, such as a dirty air filter. But the motor will automatically slow down again once the air filter has been cleaned. This leads to increased efficiency, without distracting from function.
Determining Motor Type
If your HVAC unit is older, it most likely uses a PSC motor. This is especially likely to be the case if your unit turns off when it reaches a desired temperature and then turns on again once that temperature changes. It’s also likely the case if your unit doesn’t use a thermostat at all.
If your unit has a thermostat and sometimes blows warmer air even when it’s not cold outside—or blows colder air when the air outside seems cool—but still keeps the overall temperature inside comfortable, then you probably have a multi-speed type unit. These typically use PSC motors also.
If your unit is newer, however, and continuously blows throughout the day to maintain a set temperature, you most likely have an HVAC with an ECM. If you don’t have an ECM but are considering an upgrade, it’s worth noting that ECMs may cost more upfront but they perform better and use about two-thirds less electricity.
With this deeper understanding of HVAC motors, you’re now more fully equipped to understand what your heating and cooling options are. It may also be a start to understanding any mechanical issues you may be having.
Product Compliance and Suitability
The product statements contained in this guide are intended for general informational purposes only. Such product statements do not constitute a product recommendation or representation as to the appropriateness, accuracy, completeness, correctness or currentness of the information provided. Information provided in this guide does not replace the use by you of any manufacturer instructions, technical product manual, or other professional resource or adviser available to you. Always read, understand and follow all manufacturer instructions.