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HVAC School - For Techs, By Techs

Feb 16, 2023

Chris Mohalley returns to the podcast to talk about troubleshooting the modern ECM (or EC motor) and give diagnostic tips. ECMs are electronically commutated motors; they are mechanical motors with an electronic control module that dictates everything the motor does.

As with all motors, ECMs have inputs and outputs. If the motor is not running, the first step is to check the line voltage and make sure that it is correct and connected continuously, as that's one of the main inputs on all ECMs; there is no relay or switch on the line side. The motor itself is the output, so you will know if the output is correct if the motor is rotating and generating airflow as intended. Constant-speed and constant-torque motors can all be diagnosed with a basic voltmeter.

One of the most difficult parts of troubleshooting constant-torque ECMs is knowing how the taps are programmed by the manufacturer; reading the manual and schematic is advantageous during diagnosis, especially as these motors have evolved to use pulse-width modulation (PWM) and have nine speeds instead of five (energizing pin 1 at the same time as another pin, diagnosed with 24v AC). Constant-airflow motors tend to have inputs that are less complicated than the five or nine-speed taps.

Chris and Bryan also discuss:

  • Inputs: line voltage and signals
  • TechMate Pro, multimeters, and Genteq TECINspect diagnostic tools
  • Constant-speed vs. constant-torque vs. constant-airflow motors
  • Diagnosing PWM signals with DC voltage
  • Adjusting airflow with DIP switches
  • Are board and motor failures common?
  • Why we don't diagnose the motor separately from the control


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