What is an ECM Motor?

Today’s higher efficiency equipment, both furnaces and A/C, are now using new higher efficiency motors to reduce the total electrical consumption of the system thus raising the efficiency. They also help with the efficiency by maintaining the proper air flow (CFM) across components like evaporator coils, heat exchangers, and even condenser coils. As you know from past postings, air flow is critical to proper operation, but, the use of ECM motor technology, also help raise efficiencies of the equipment.

So, what is an ECM motor?  An ECM motor is some times referred to an a variable speed motor. In one sense, this is true, it does vary its RPM of the motor, but only in response to changing conditions in the system.  But in the truest sense, all it trying to do is maintain a programmed CFM.  ECM stands  for Electronically Commutated Motor

The ECM motor has 3 components:

  1. The motor — which does not have any “windings” in it.  The stator is driven by magnetic fields.  The motor operates off DC voltage. When it first starts, it will actually rock back and forth before starting as it aligns the magnetic fields to drive the motor. The same motor will operate on both 110 volts and 220 volts, depending how the 5 pin power plug is configured. Rarely, does this go bad. The most common  failure is due to someone “dropping” the module while it is plugged into the motor and breaking the wires going into the motor.
  2. The module or ECM Microprocessor — or the “brains” of the motor.  It receives the programming information from the board via a 16 pin harness and “translates” it so the motor produces the CFM desired.  It mounts on end of the motor or can be remotely mounted and stores the “relationship” between “speed, torque, & airflow”. It is programmed at the factory to match a given unit Each module is “specific” to a model and are not interchangeable.
  3. Lastly, there is some sort of control board where you can set the desired CFM for each application and that is connected to the module with the 16 pin harness.

The way I explain it in my training classes is this.  An ECM motor maintains a programmed CFM in response to changes in torque. When the sensed torque changes, the RPM of the motor either ramps up or down to maintain the programmed CFM.  Sounds confusing, doesn’t it?

Let me put it to you this way.  Let’s compare how an ECM motor works to cruise control on a car.  When you are using cruise control, you “program” how fast you want the car to go and set that speed (MPH). The RPM’s of the engine run at a certain level to maintain that speed.  Now, you car starts to go up a hill. The cruise control senses a change in torque, so it needs to “rev” up the engine so it can maintain your “programmed speed”.  Likewise, when you go down a hill, there is less torque on the engine so the RPM’s are reduced and, again, you are maintaining the programmed speed.

The same thing is occurring with an ECM motor.  It works on a relationship between RPM, torque, and CFM (instead of MPH).  Instead of a control on the steering column, there is a board in the unit that you need to set up with the “cool”, “adjust”, “heat”, and “delay” profiles (switches, jumpers, etc, depending on manufacturer).  Once you have programmed the desired CFM for a particular application, the motor and module do the rest.

Let’s say you have a 3 ton air conditioner. So we need  400 CFM per ton or 1200 CFM to work properly.  You use the programming board and set BOTH the cool and adjust profiles for as close to 1200 CFM as you can. (Always use the manufacturer’s tables for setting up an ECM motor).  Now, on a call for cooling, the motor turns on and is going to try to maintain your programmed CFM. Here is where added efficiency comes in because we are maintaining ideal CFM across a range of operating conditions.  Of course, as an air conditioner runs, the evaporator is going to get “wet” since we are removing latent heat and humidity.  When the coil gets wet, the static pressure of the system goes up.  As the static goes up, the motor senses a change in torque (like the car going uphill) and starts to increase the RPM of the motor in order to maintain the CFM of the system.  Same thing occurs as a filter gets dirty,  return static increases and the motor revs up the  RPM to maintain the CFM.  Now, as the latent heat decreases and there is less humidity or water on the coil, or someone changes the dirty filter, there is less static, a reduction in torque, so the RPM’s decrease, all the time maintaining  CFM.

The same thing occurs in heating mode.  You have programmed the motor to maintain a desired “temperature rise” for the system.  The motor will deliver that CFM to maintain that rise.  But, again, if the filter is gettng dirty, the motor’s RPM will increase, to maintain the CFM and temperature rise.

Lastly, you can also program a DELAY profile on the CFM board. This function is only for cooling but it allows you to further “fine tune” how the motor ramps up and down at the start and end of a call for cooing.  You can set a “Normal, Humid, Dry, or factory default profile through the control.

By maintaining proper CFM in cooling, and temperature rise in heating, we get the maximum efficiency out of the furnace and air conditioner. This, coupled with the fact that an ECM motor uses less wattage than a PSC motor, you can see why these motors are becoming more and more popular as part of a total energy-efficient system.

In my next post, I will try to discuss some “diagnostics” for ECM motors  to try to further take the “mystery” out of these motors.

About yorkcentraltechtalk

I have been in the HVAC industry most of my life. I worked 25 years for contractors on anything from residential to large commercial boilers and power burners. For the past 23+ years I had been employed by York International UPG Division ( a division of Johnson Controls) as a Technical support/Service Manager but I am now retired. One of my goals has always been to "educate" dealers and contractors. The reason for starting this blog was to share some knowledge, thoughts, ideas, etc with anyone who takes the time to read it. The contents of this blog are my own opinions, thoughts, experiences and should not be construed as those of Johnson Controls York UPG in any way. I hope you find this a help. I always welcome comments and suggestions for postings and will do my best to address any thoughts, questions, or topics you may want to hear about. Thanks for taking the time to read my postings! Mike Bishop
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20 Responses to What is an ECM Motor?

  1. roger daigle says:

    Hey Mike, GREAT series on ECMs. I know that retro ECMs are available for existing systems. What all is involved in changing a psc system to an ECM?

  2. Rebecca Willocks says:

    Hello, Mike. Thanks for your explanation of EC motors. Sometimes I see in specs where ECMs are required to have a potentiometer dial. Is this a standard feature in the “brains” of the motor? Also, are ECMs considered high efficiency motors?

    • ECM are high efficiency motors. I have not seen a potentiometer ever used on these type of motors. they have a CFM selection board that sets the application cfm and the moptors are programmed by the individual manufacturer to meet the specs of the unit they are going into.

  3. Jim says:

    Do these motors have built in relays. I have a Payne indoor air handler for my heat pump. Im in the army now but 11 years ago I was a AC tech. I am used to seeing at least a fan relay or fan control card and an external capacitor for the PCS blower motor. Now I see only two relays for the auxiliary heat elements and a blower motor with no capacitor. I have 230v going to the motor direct through the plug. then I have fan speed wires blue for cool and white for heat. I have 24 v going to fan and I hear tones coming from the fan motor and in the heat mode the fan lurches back and forth but refuses to spin. Is the fan defective? Payne M# PF4MNB031 motor M# 5SME39HXL163. I would appreciate any help I can get.

  4. Pingback: 4 Ways to Upgrade an HVAC System

  5. rolland says:

    thanks for the education

  6. Pingback: What is an ECM Motor? | Commercial HVAC and Refrigeration Services in Massachusetts and Rhode Island

  7. Renz says:

    I found this forum and I am loving it ,there is good info here for beginners tech like me.

    Thank so much.

  8. Norm Jenks says:

    Question: Can these motors be used with an inverter power supply that is not pure sine wave. Also can it be used with a generator.

    • in most applications — NO! Most circuit board will not work properly with inverters or generators that are not true sine waves. If the generator is true sine wave, most furnaces and ecm motors will work properly. As alway, it is best to check with your manufacturer or with Regal Beloit who makes the ECM motors for definitive answer

  9. Chad Y says:

    Do you know anyone who supplies larger horsepower ECM motors? Looking for something other than AC motors ran off a vfd, had a couple recent instances of electrical discharge causing the motor bearings to fail.

  10. Stuart says:

    Mike- I’m currently doing some research in this space, and your blog and some of your posts on HVAC and ECM motors has been very helpful. I was actually wondering if you might be willing to set up some time to talk–is there an email address or best way to get in touch with you?

  11. Luc says:

    3rd REQUEST!!!

    I purchased a York Heating and A/C unit in 2007. Im have been a customer of York for over 20 years. The fan motor died after 8 years and I am told by my dealer and your office in Ottawa that the motor costs $3,248.00 (!?!?!?) I paid $1,590.00 for the whole unit! I cannot believe that the motor is not covered by a warranty and dies just after the warranty expires. I am selling my house to build another on and I am told by my dealer to go with another company(!?!?). I went with York for quality, reliability and peace of mind. Is there not something that York can do in this kind of situation?


    • Sir:
      I am retired from JCI/York Chicago Branch for over 1 1\2 years. You need to contact your local distributor in Canada. I agree that the qouted price is probably incorrect. As far as warranty, what is the serial number of the furnace?
      If you get no satisfaction from the dealer or distributor, then I suggest contacting Consumer Relations at http://www.york.com and maybe they can intercede with the distributor and the dealer.
      Beyond providing this information, there is nothing else I can do.

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