ECM - Here to Stay
Electronically Commutated Motors (ECM) are becoming commonplace in the HVAC Industry. The ECM offers: higher efficiency over a broad speed range motor, a lower noise level, programmability, and a lower operating cost (www.hvacexcellence.org
Although direct current motors have been in use for over a century, their use is low compared with the use of alternating current induction motors like PSC, CS, and CSCR motors. The difficulty of dealing with conventional DC motors is the wear on the brushes and their eventual replacement. ECM, or brushless DC motors, do not have this disadvantage.
The ECM motor has permanent magnets in the rotor and the stator has electrically excited windings. In order for the rotor to turn, the windings on the stator must reverse polarity continually. A brushless commutator placed on one end of the rotor provides the signal to the stator windings to reverse polarity. An integrated circuit times the switching of the electric currents to the stator. A programmable chip is often used with ECM motors to provide multispeed capabilities.
ECM motors are commonly used in forced-air furnaces that have two-speed operation on the forced-air blower. Unlike AC motors, DC motors maintain their high efficiency over a wide speed range, and can provide continuous fan circulation at low speed with only modest energy consumption.
ECM Service Tips, from the GE ECM Service Guide
Tech Tip 1: Don't automatically assume the ECM motor has failed. Make sure you go through the diagnostic steps completely before replacing the motor.
Tech Tip 2: When it's necessary to disconnect the power from the HVAC system, it's always a good practice to verify that voltage has been disconnected, by using a voltmeter.
Tech Tip 3: A True-RMS meter isn't needed to check high-or low-voltage to the motor.
Tech Tip 4: If you must replace the 2.0, 2.3, or 2.5 control module, then be sure to use a direct replacement from the manufacturer. ECM control modules are factory programmed for specific manufacturer applications. If you use the wrong control module, it will void all product warranties and may result in improper or no blower operation.
Tech Tip 5: If a check of the control module indicates replacement is required, then also check the motor module. Installing a new control on a failed motor will result in the new control also failing.
Tech Tip 6: Always pull the connector and not the wires. Most connectors are also keyed. Reconnecting a connector the wrong way could damage the motor.
Tech Tip 7: When checking any plug connector, the meter leads are most likely larger than the terminals or socket. Using thin leads will prevent the terminals from being damaged by a voltage check.
For complete guidelines, refer to the accompanying service manual.