Electric motors are an important part of HVAC systems. From powering blowers and water pumps to compressing refrigerant, electric motors perform some of the most basic functions that allow HVAC systems to do their job. Without them, we wouldn’t have access to heating and cooling as we know it.
Though they’re all designed to power a wide range of components, they’re not all created equal. In some cases, one type of motor will be favorable over another and by determining what function needs to be performed, we can determine which motor is most suitable for the task. ECM and PSC motors are two comparable motors, but they work in very different ways. These differences are an important part of their designs and they each have their intended purpose.
What Is a PSC Motor?
A PSC (permanent split capacitor) motor is designed with only two functions in mind: it turns on and it turns off. Because of its limitations and primitive design, the speed of a PSC motor cannot be controlled or altered, and when powered on, it runs at full capacity only. This constant speed means that, while it performs powerfully, it doesn’t do so efficiently and energy is wasted in the process.
What Is an ECM?
An ECM (electronically commutated motor) is a motor designed to perform similar tasks to a PSC motor but introduces variable speed. An ECM can be modulated and controlled to manipulate its behavior to meet the condenser’s call for airflow. Unlike a PSC which only has two stages, an ECM has many different speed settings that allow it to increase and decrease gradually rather than starting abruptly at full capacity. Its design makes it a more efficient and effective motor that has the ability to save a great deal of energy.
Any time that a fan or motor offers speed modulation, it will likely be the most efficient option. In the case of PSC motors and ECMs, this rings just a true and an ECM can offer the diversity that a PSC motor simply cannot.
Because of its variable speed settings, the energy required to power an ECM can be lowered or raised according to demand and will never perform at a higher speed than necessary. When the condenser fan doesn’t need to be running at full speed, the ECM can adjust its speed and save energy. A PSC motor, on the other hand, will always run at full speed, even when it’s not necessary. The lack of modulation, in this case, means that extra energy is being wasted to do the same job that a fan running at a fraction of its speed could do. It also means that a PSC motor is much louder compared to an ECM.
Like its name suggests, an electronically commutated motor is hooked up to an electronic control module. The module is programmed at the factory to perform a specific function, though it can be particularly sensitive to power issues and grounding issues. Before working with the control module, it’s important to disconnect any power running to it or the motor. Aside from the module, the motor itself requires a low level of maintenance. The use of ball bearings in an ECM means that it can run effectively for a long time without requiring lubrication. The gradual start and stop also has a positive influence on its lifetime and the reduced impact is easy on parts. In this same way, a PSC motor may require increased maintenance due to its sudden start and stop motion.
A PSC motor has been a standard in the HVAC industry for years, however, and they continue to be used today. Not only are they simple and inexpensive, but they’ve proven to be an extremely reliable component. The average lifespan of a PSC motor is around 40,000 hours, though an ECM surpasses it at 90,000 hours. Ultimately, an electronically commutated motor’s design bests that of the permanent split capacitor motor in almost every way.
Overall, the use of an electronically commutated motor can decrease energy usage by as much as 75% compared to a PSC motor. Not only will an ECM save on energy, but it will also provide more even and effective performance that will meet the demands of your condenser, however high or low that may be without wasting addition energy.
5 thoughts on “ECM Condenser Fan Motors vs. PSC Motors”
What might be the average annual KW/H rating to some of the 95/96 AFUE two stage gas furnaces seeing as how they have more electronic devices in them now and are always plugged in so to speak? And of course it depends on the actual usage of the furnace, say in zone 4. Ballpark figure? Thank-you Peter
How Much the price gap between PSC and ECM Motor?
From a service tech;
Considering repair, outside of the 10 year parts warranty period
– PSC motor parts cost typically runs me $70-$150.
– ECM motors usually only lose the module, but we can’t always get the module separately.
Module only; $85-180
Motor + Module; $200-500
Sometimes an ECM motor will be known as an “X13” motor, which includes a simplified module with 3-5 pre-programmed speeds. These are cheaper, but fail to take advantage of some features in communicating systems. An X13 motor will usually split the price difference between a normal ECM motor and a PSC motor.
PSC motors are still offered in some 14 SEER “basic” or “contractor grade” systems, but are being aggressively phased out due to government manufacturer efficiency requirement increases. All matched 15-17 SEER “better” or “two stage” systems will include at least an X13 indoor blower motor, and towards 17 SEER you can get ECM tech on the condenser fan motor as well. Anything higher than 17 SEER will get ECM blower and condenser fan motors, some high end gas furnaces will have ECM inducer blower motors, and the 18-20+ SEER compressors are all either using a ECM/inverter drives, electronic internal staging valves, or a combination of the two (I believe Lennox leads the pack on compressor efficiency, but I don’t know much about the durability and resistance to installation error with Lennox)
I would like to have an appointment with an expert of air conditioning using all this ECM system and the R410system.
I have two air conditioning units, one unit has ecm motor and the other has psc motor.
the unit that has the psc works very good for 15 years
the unit that has the ecm motor, I have changed three times in 5 years, so where is the savings?
ecm motor is very expensive, so the last time the ecm motor was damaged, a psc adapted and is working very well.
the psc may not be as efficient, but it is more durable
The engine ecm was easily damaged.