Checking ECM Motors

Electronically Commutated Motors (ECM) are pretty common these days. You can’t troubleshoot them the same way you do a standard PSC motor. The ECM motor is really two components – a motor and a control module. One big difference in checking these motors is that is that they receive voltage all the time, not just when the motor is operating. Really, it is the module that is powered all the time – the module then controls when the motor receives power. The first thing you want to establish is if the problem is in the controls to the motor/module, or the motor/module itself. A device called a TECINSPECT helps you do this. Turn off power to the unit. This step is important, not just for your safety, but for the motor’s safety. Unplugging connectors from the motor while the unit is powered up can cause the module to arc out. Unplug the control plug from the module and connect the TECINSPECT. Connect the two tecmate alligator clips to 24 volts, such as the R and C terminals. Turn power back on to the unit. The LED on the TECINSPECT should light to show it is receiving 24 volts. Flip the TECINSPECT switch on and the motor should operate. If it does, the problem is in the control board or wiring harness from the unit. If the motor does not operate, the problem is in the motor or module. If the problem is in the motor or module, the odds are that it is the module. Turn the power to the unit back off and wait 5 minutes for the high voltage capacitors inside the module to discharge. Remove the module and unplug it from the motor. Ohm out the motor. The resistance between any two of the three motor leads should be approximately 5 ohms. If the readings check out, the problem is in the module. You must replace the module with one designed for that specific unit because the mmodules are programmed for the blowers they control.