PWM Signal from ECPM03 Troubleshooting - TELCO Motors

PWM Signal from ECPM03 Troubleshooting - TELCO Motors

Some products are equipped with Electrically Commutated Motors (ECM), which are variable speed motors.  These motors are controlled by a Pulse Width Modulated (PWM) signal.  That signal can originate from a speed controller within a fan or make up air product, such as the MSC controller, or from an external control box such as a Hood Electrical Control Panel (ECP).

This page contains testing procedures to determine if the PWM output from a hood control prewire is functioning properly to control an ECM fan.  The intended audience is a mechanical contractor or licensed electrician.
  1. Before starting the troubleshooting process, ensure that the fan circuit breaker is in the ON position.
  2. Ensure the hood controls are calling for fans to be on.
  3. Verify the motor has the correct applied line voltage:
    1. If the brand is Telco, the motors are voltage specific and you can verify the input voltage on the motor matches the supplied voltage.
    2. If the brand is Nidec, please verify that the motor has the appropriate jumper in place for either 120V or 240V 1ph 60hz AC power.

  4. Care should be taken to ensure the PWM terminals are not shorted. This can result in damage to the ECPM03 board and will not be covered under warranty.

Step 1 - Making sure the ECP and Fan is operational.
1. If ECP is energized, skip to step 2.
2. Using a voltmeter, verify that the correct voltage is present to the fan disconnect.
3. If disconnect is in the ON position and the motor is not running, check the following.
  1. Shielded twisted pair wiring is ran between the fan and the ECP per the factory wiring schematic.  This field run wire is what transmits the PWM signal from the prewire to the fan controller within the fan.
  1. Shielded twisted pair is landed correctly in the ECP per below. Terminals PxA/PxB where A is positive (red), and B is negative (black).
     

Make sure the shielded twisted pair is landed correctly on the fan controller per below.
  1. If the motor is still not running and wiring/voltages are correct, there may be an issue with the ECPM03 programming.  Please see step 2 below.

Step 2 - Making sure the ECPM03 board is programmed correctly.
1. Ensure the ECPM03 is programmed for the correct number of ECM fans. This will enable the PxA/PxB output on the ECPM03 board.


2. Check to make sure the fans are assigned to the correct zone and that the speed settings are set correctly.

         
Step 3 - Verifying output from the ECPM03 board to motor.
1. Take voltage readings using the chart below. First readings should be with the fan speed set to 50% and then a second reading should be taken when the fan speed is set to 100%. Voltage should change from 12VDC to 24VDC.
2. If the voltages do not change, or you do not have any DC voltage output and you have double checked all the settings, double check the wiring connections and/or replace the ECPM03 board.
Example motor part numbers below.
Highlighted text indicates 42 or 48.


Fan speed set to 100%
+ lead on red wire / - lead on yellow wire
Voltage should be 24 VDC +/- 10%

Fan speed set to 50%
+ lead on red wire / - lead on yellow wire
Voltage should be 12 VDC +/- 10%

With fan speed set to 50%, measure the DC voltage across the yellow and red wire.
The voltage at 50% should be 12 VDC.
Care should be taken with meter leads as to not damage the connector.
If DC voltage is correct at 50%, adjust the speed to 100% and the voltage should be 24 VDC.
On a makeup air unit, the voltages can also be verified at the end of the harness extension.
Be aware that the yellow wire changes to a black wire on the MUA extension harness.