Part three of this three-part series on indoor blower ECMs provides information about diagnostics and replacement.
In Parts 1 and 2 of this series (published in the June and August 2020 issues, respectively, of RSES Journal), I discussed how to adjust airflow and the airflow performance characteristics of EC indoor blower motors. The information in those articles can also be used for diagnosing operating ECMs that exhibit airflow related issues such as:
- The HVAC system is tripping the main limit (gas or oil heating systems), the compressor overload is tripping (heat pump systems in the heating mode), or the indoor coil is freezing (heat pump systems in the cooling mode);
- The system noise in any stage of operation, including continuous fan, is objectionable; or
- The outlet air temperature is objectionable.
In this article, I will focus on diagnosing the ECM when it is not operating. EC indoor blower motors are commonly designed with two separate inputs for proper operation: 1The line voltage that powers the ECM; and 2the communication that provides the on/off command as well as the operating value (speed, torque or airflow). Both of these inputs are necessary for the ECM to operate.
Constant Airflow ECMs
Figure 1 is an example of two commonly used constant-airflow ECM connections. On both motors, the 5-pin connections are the line-voltage inputs. The 16-pin and 4-pin connections are the communication inputs. The pin structure of the communication input does not always relate to the type of communication used. There are several different methods of communication that can be used between the HVAC system control board and the ECM. The three most commonly used are called the thermostat mode, pulse-width modulation (PWM), and digital serial interface (DSI, also referred to simply as “serial communication”).
Some ECMs are capable of operating with multiple types of communication in- puts. Others may be designed specifically for one type. The method used is selected by the HVAC OEM to match its control board outputs. Many HVAC system manufacturers have used and may still use all three types of communication in their different models or generations of models.
Due to the complexity of each communication type and the ability of each OEM to customize the inputs, most diagnostics for constant-airflow ECMs are designed to prove either the existence of communication to the motor control or operation of the motor with a test input to the motor control. There are two commonly accepted conclusions to these tests:
- If the ECM is receiving the proper communication input, it should be operational in all modes of operation; and
- If the ECM operates with a test input, it should be operational in all modes of operation.
The following paragraphs discuss the different types of diagnostics used to troubleshoot constant airflow motors.
Figure 1: Typical ECM connections.
On-board diagnostics—On-board diagnostics (located on the HVAC system control board) provide a run test of the ECM. Many HVAC system manufacturers have this capability built into their control boards or communicating interface controls. Where applicable, the unit label may provide the instructions on how to operate this test. Detailed information on these tests can be found in the installation or service manuals.
Pin-to-pin diagnostics—Pin-to-pin diagnostics (sometimes called “pinout” diagnostics) of the communication inputs to the ECM require the use of an ac/dc voltmeter. Technicians must be able to read detailed troubleshooting diagrams found in the HVAC system manufacturer’s literature. Such diagrams, related to each HVAC system demand and airflow or comfort setting, may be located in the installation manual, the service manual or in an application guide developed specifically for ECM-driven systems.
Special-purpose diagnostic tools—Some diagnostic tools designed for use with ECMs may be applicable only to specific HVAC models, motors, or communication types:
- The HVAC system manufacturer may provide special diagnostic tools that can initiate a run test and/or confirm the communication (output) information from the control board. These tools are specifically designed to diagnose the particular HVAC system for which they are built. Even if another HVAC manufacturer uses the same model motor and communication type, the diagnosis may be inaccurate.
- The motor manufacturer may have its own diagnostic tool that provides a run test of the ECM. These tools typically are designed to diagnose a particular brand of ECM (that may be used in any HVAC system) and may be compatible with multiple communication types and multiple model generations.
- The meter manufacturer may provide tools for diagnosing the communication outputs from the HVAC system control board and/or performing a run test on the ECM. Always consult the literature supplied with any diagnostic tool that does not come from the HVAC OEM or motor manufacturer to be sure that it is compatible with the HVAC system and/or ECM you are troubleshooting.
On-board diagnostics, pin-to-pin diagnostics and special-purpose diagnostic tools provided by HVAC system manufacturers all vary in use and function. All of these methods require the use of the diagnostic instructions provided by each HVAC system manufacturer.
Figure 2: ECM plug connector.
Special-purpose diagnostic tools provided by motor manufacturers are specifically designed to provide simplified diagnostics on their motors regardless of the application. In this article, I will show how to diagnose Genteq® constant airflow communicated ECMs using the Genteq® TECINspect® diagnostic tool. It should be noted that other ECM manufacturers also provide similar diagnostics tools for their communicated ECMs. Always follow the instructions provided by each HVAC system manufacturer or motor manufacturer related to their diagnostic tools and methods.
Figure 3: Checking the line-voltage input.
Diagnosing the line-voltage input to the motor control—Almost all constant- airflow ECMs are supplied with line voltage whenever the HVAC system is powered and the door interlock switch (if applicable) is closed. A demand call from the thermostat is not required to check this voltage.
- Disconnect the line-voltage power to the HVAC system;
- Disconnect the line-voltage plug at the motor control;
- Restore power to the HVAC system; and
- Check the line voltage to the appropriate pins with an ac voltage meter.
Figure 2 on pg. 25 is a picture of a common 5-pin connector that is used for line-voltage input. Notice the latches on both sides of the plug.
Many constant-airflow ECMs have dual-voltage capability (120 or 208-230 V ac). The wiring of the plug matches the line voltage used. Look at Figure 3. The example at the top shows how a jumper is installed in pins 1 and 2 when the ECM is to be operated at 120 V ac. When the jumper is left out, the line voltage required is 208–230 V ac. If the wrong voltage is supplied to the motor control in relation to the wiring of the plug, the motor control may not operate properly or may be damaged.
Most ECMs will operate properly with line-voltage values of ±10% of their nominal ratings. This specification is determined by the motor manufacturer. If the voltage measured at the plug is outside the acceptable range, check the line voltage harness and the power supply to the HVAC system. After the problem has been corrected, disconnect the power to the HVAC system and properly reconnect the plug to the motor control.
If the ECM now operates with a thermostat demand, the problem is solved. If the ECM still does not operate or if the voltage was within the acceptable range to begin with, continue with the communication diagnostics.
Diagnosing the communication input to the motor control—The following diagnostic example relates to Genteq® ECM motors using the Genteq® TECINspect® diagnostic tool (see Figure 4). This tool provides both a 16-pin and a 4-pin communication connection. Note: These instructions also apply to the Genteq® TECMate™ Pro diagnostic tool.
The following step-by-step procedure applies to any HVAC OEM system that utilizes Genteq® ECM models 2.0, 2.3, 3.0, and Eon.
- Confirm or correct the line voltage to the motor control. Make sure that the line voltage plug is connected properly.
- Before restoring power to the HVAC system, disconnect the system communication control harness from the ECM and connect the TECINspect® 16-pin or 4-pin connector. Note: The TECINspect® initiates an operating test. Do not remove the ECM from the blower assembly. The blower assembly can be left in the HVAC system. The test will work with the blower section out of the HVAC system—however, a good ECM may operate erratically without the blower wheel attached.
- Attach the two leads with alligator clips from the TECINspect® to a 24-V ac power source (such as the thermostat’s “R” and “C” terminals), or directly to the transformer.
- Set the switch on the TECINspect® to “off ” and restore power to the HVAC system.
- Confirm that the green LED in the switch on the TECINspect® is illuminated (see Figure 5). If the LED is not illuminated, either the 24-V ac leads are not connected to a 24-V ac power source or the TECINspect® has failed. Voltage higher than 30 V ac connected to these leads will permanently damage the TECINspect®.
- Set the switch on the TECINspect® to “on.”
If the ECM operates with the TECINspect® diagnostic tool, but will not operate when connected to the HVAC system control board, the reason the ECM is not operating is unrelated to the ECM. The issue is before the ECM. Reference the HVAC system install/service manuals or contact the HVAC system technical support department for diagnostics. If the ECM does not operate with the TECINspect®, replace the ECM.
Figure 4: TECMate PRO
Figure 5: Set up.
Constant Torque ECMs
Constant torque ECMs are also built by multiple motor manufacturers. The most common design for constant torque ECMs include the following attributes:
- Line voltage connections at the motor are labeled “L” (Line 1), “G” (Ground), and “N” (Neutral). The “N” terminal is connected to the neutral line on 115 V ac and 277 V ac systems, or to Line 2 on 208–230 V ac and 460 vac systems. Each model is built to operate at a single voltage source.
- Line voltage power is continuously supplied to the ECM regardless of a demand call from the thermostat.
- The speed taps are designed similar to a multi-tap PSC induction motor.
- The speed taps are energized with 24 V ac. This voltage selects the speed (torque) value and doubles as the on/ off communication.
Figure 6 illustrates the most commonly used connection block on these motors.
Diagnosing the line-voltage input to the ECM motor control—A demand call from the thermostat is not required to check this voltage.
- Disconnect the line-voltage power to the HVAC system.
- Disconnect the line-voltage plug or individual wire connections to terminals “L” and “N” at the motor control.
- Restore power to the HVAC system.
- Check the line voltage to the plug terminals or wires that connect to terminals “L” and “N” (see Figures 7 and 8).
- Check the HVAC system schematic for the correct line voltage value to be applied to the ECM. Most ECMs will operate properly with a line voltage of ±10% of the nominal rating. This specification is determined by the motor manufacturer.
If the voltage measured at the appropriate terminals is outside the acceptable range, check the line-voltage harness and the power supply of the HVAC system. After the problem has been corrected, disconnect the power to the HVAC system and properly reconnect the plug or wires to the motor control.
Figure 6: Electrical connection details.
Figure 7: Checking voltage on the X13 with connector plugs.
Figure 8: Checking voltage on the X13 with individually connected terminals.
If the ECM now operates with a thermostat demand, the problem is solved. If the ECM still does not operate or if the voltage was within the acceptable range to begin with, continue with the speed tap diagnostics.
Diagnosing the speed tap voltage input to the ECM motor control:
- Disconnect the line-voltage power to the HVAC system.
- Disconnect both plugs or the individual wire connections to terminal “C” and the tap (1–5) to be diagnosed at the motor control.
- Restore power to the HVAC system.
- Confirm the presence of 24 V ac to the plug terminals or wires that connect to terminal “C” and the tap (1–5) to be diagnosed (see Figures 7 and 8). Note: The HVAC OEM may not program all taps. Consult the system schematic or manual and confirm that the tap receiving voltage is intended to be an operational tap.
If the ECM is not receiving the proper tap voltage the reason the ECM is not operating is unrelated to the ECM. The issue is before the ECM. Reference the HVAC system install/service manuals or contact the HVAC system technical support department for diagnostics. If the ECM is receiving the proper tap voltage and continuous line-voltage power, but does not operate, replace the ECM.
Constant Airflow and Constant Torque ECM Replacement
There are two options for the replacement of these motors.
Original Equipment Manufacturer (OEM) ECM—To replace these motors with a factory original motor contact the HVAC system manufacturers’ authorized distributor and provide them with the model number of the HVAC system. These motors are programmed to match the operating characteristics of the original motor. However, depending on the age of the motor, the replacement motor may be slightly different or may not be available from the OEM.
Aftermarket ECM Designed Specifically to Replace OEM ECM Motors—Multiple ECM manufacturers now offer retrofit replacements for OEM ECM motors. Genteq® Evergreen® ECM is one example of these motors (see Figure 9).
- Evergreen® EM motors replace any OEM constant torque ECM built with 24-V ac speed taps. They are built with the most common plug used by ECM manufacturers for ease of connection. Airflow adjustment is as simple as moving the input from one tap to another.
- Evergreen® VS motors replace constant airflow (variable speed) ECM built by Genteq® (including motors formerly branded GE). They can replace both 16-pin and 4-pin communicated motors. Airflow adjustment is as simple as a button push on the user interface when replacing 16-pin motors. When replacing 4-pin motors the VS works exactly like the OEM motor.
Figure 9: Aftermarket ECMs and retrofit component.
Figure 10: Constant torque EC motor control.
Some HVAC OEM and motor manufacturers offer the ability to replace the motor control separately from the motor. ECM motors are actually two components, an electronic control often referred to as the “motor control” and the mechanical motor often referred to as the “motor module.” Figure 10 is an example of a motor control replacement for a constant torque ECM.
The motor diagnostics provided here relate to both constant airflow and constant torque ECM motors. However, the illustrations use a constant airflow motor. Motor diagnostics are necessary only when the motor control and motor are constructed as detachable or separate components, and their individual replacement is supported by the motor and/or HVACR system manufacturer. The following diagnostics of the motor assume that the proper communication and/or line-voltage inputs to the motor control have been verified but that the motor will not start or operates improperly.
Figure 11: Separating the motor control from the motor module.
Diagnosing the motor module
- Disconnect the power to the HVAC system.
- Disconnect the line-voltage input (plug/wires) from the ECM.
- Disconnect the communication input (plug/wires). Warning: Wait five minutes for the internal capacitors to dissipate before continuing to the next step.
- Remove the two 1/4-in. hex head bolts from the end of the motor control (refer to Figure 11). These bolts attach the motor control to the motor module. Cradle the motor control so that it does not fall.
- Gently rock the motor control away from the motor module. Carefully reach in between the motor control and the motor module and disconnect the 3-pin harness from the motor module at the motor control. Depress the latch to release the plug.
- Perform the following tests on the 3-pin plug connected to the motor module:
a. Phase-to-phase test. Ohm out the phases from pins 1-2, 1-3, and 2-3 in the plug. Start at either end of the plug for this sequence. Set the ohm meter to the lowest scale. If the readings are all less than 20 Ω and within ±10% of each other, the motor passes this test (see Figure 12). If any two pins measure infinity (∞) or “Open,” there is an open winding and the motor has failed. If any two pins measure zero or continuity, there is a shorted winding and the motor has failed.
b. Winding test. Ohm out the motor windings from each pin in the connector to the ground, using the endshield or recessed motor brace as ground. Set the ohmmeter to the highest scale (except megohms). If all of the readings are above 100,000 Ω (100 kΩ), the motor passes this test. Typically, a good motor will show all readings as infinity or “Open.” If any of the readings are below 100,000 Ω, the motor has failed. The typical failed reading is zero or continuity, indicating that the motor is shorted to the ground. Meter manufacturers use various digital displays to indicate an open circuit. The most common display readouts are “I,” “OL,” “Open,” or the infinity symbol ∞ (see Figure 13).
- While the motor module is still disconnected from the motor control, rotate the shaft by hand.
- If the motor module passes both of the ohm tests and is easily rotated by hand (a slight cogging feeling is normal), replace only the motor control. Follow the instructions supplied with the new motor control for installation and re-assembly.
- If the motor module fails either the ohm test and/or is difficult to rotate by hand, replace both the motor control and the motor module.
Figure 12: Phase-to-phase test control.
Figure 13: Winding test.
An ECM is a complex, microprocessor- driven motor that incorporates electronic controls with a mechanical motor. How- ever, from a user's point of view, these motors are not that difficult to operate, adjust or diagnose, if you know what they require to operate properly. It is my hope that this three-part series has provided you the basics to get comfortable installing, servicing, and diagnosing ECM motors. Keep in mind that the information I provided is just the basics. The rest of the information is found in the HVAC system manuals. Being a constant student of these manuals is what helped me become a confident and competent technician. It will also help you keep up with the continuous changes in technology. As I always say, “Never Stop Learning!”.
Christopher Mohalley is the Training Manager for Regal Beloit America Inc. He has applied his 25+ years of HVAC field experience, instruction and extensive product training to create a nationally-recognized ECM training program. He serves as a NATE Technical Committee SME, is a Member of RSES and is NATE certified in all HVAC disciplines. Genteq®, Evergreen®, TECMate Pro® and TECINspect® are trademarks of Regal Beloit Corp. or one of its affiliated companies. For more information about Genteq® Evergreen® motors please visit www.ECMMadeEasy.com.
Interested in reading more about this topic Check out Mohalley’s book Understanding Electronically Commutated Motors (SKU 200-523x), published as a part of the RSES Sustainability Series at www.rses.org/store. Use promo code ECM2020 and get 10% off the purchase price.
"Part 3: EC Indoor Blower Motors, Resistance Is Futile", by Christopher Mohalley. October 2020 feature reposted with permission from RSES Journal, www.rsesjournal.com.