What Causes ECMs to Fail?
When applied properly, Electronically Commutated Motors (ECMs) are very reliable and offer long life. However, just like Permanent Split Capacitor (PSC) induction motors, when applied to an application that they are not designed for, their life cycle will be shortened.
A major cause of failure occurs when a blower is applied to an application with static pressure above .8” WG. This not only shortens the life of an ECM, but also a PSC. With an ECM this will cause a failure of the metal oxide varistor (MOV), a disk in the controller. If the MOV has failed, it would typically be discolored, cracked, or broken apart.
The MOV can also be damaged if the motor has been exposed to electrical surges or lightning strikes. If the power supply is prone to brown outs or other causes for voltage variations, this could result in damage to the MOV.
Another major reason for failure is moisture. With blowers, ECMs are applied in high efficiency applications. This can result in the presence of condensation. Motor manufacturers have taken precautions to protect the motor from this condensation by applying potting material around the connections in the controller. This is typically seen as a black, rubbery material covering the electrical connections in the controller. If an attempt is made to replace components in the controller, it could damage this material and lead to moisture exposure. This could result in a service call-back.
As a technician you can help prevent damage to the motor from moisture by ensuring that when the motor is installed, the connector on the motor is as close to “down” as possible. Also form a “drip loop” in the leads near the connector of the motor. This will direct any water rolling down the leads to fall off the leads at the bottom of the loop, and not enter the connector.
Connector shown in down position with drip loop in leads
By assuring that the static pressure for the system is appropriate and the motor is installed to protect against moisture, the ECM will provide excellent longevity!