ECM-VCU-RTC Troubleshooting - TELCO Motors

This guide outlines the troubleshooting steps for the ECM-VCU-RTC fan speed control (FSC) when used with TELCO Electrically Commutated Motors (ECM).

This guide will help to determine if the motor is bad or the speed control is bad.

The information below contains testing procedures to determine if the speed control is functioning properly.

This guide only applies the to ECM-VCU-RTC speed controller (yellow housing). This guide is not applicable for the MSC speed controller (blue housing).

The expected audience for this guide is the licensed mechanical contractor or licensed electrical contractor.

Before starting the troubleshooting process, ensure that the fan circuit breaker is in the ON position.
Ensure the hood controls are calling for fans to be on (if line voltage is being fed from contactor in ECP).
Telco motors are voltage specific.

Step 1 - Making sure the speed control is operational.

If speed control display is illuminated, skip to step 2.
Using a voltmeter, verify that the correct voltage is present to the fan disconnect per the fan wiring schematic and specification.
If disconnect is in the ON position and there is no display, check the following.

Voltage at the primary side of the step down transformer.
Voltage (24V AC) at the secondary side of the step down transformer.
Voltage across the 24V AC terminals on the speed control.

4. If the voltages are present and the display is still not working, the speed controller should be replaced.

Step 2 - Making sure the speed control is programmed correctly.

If the speed control display is illuminated and the fan will not run, it is important to first make sure the speed control is programmed correctly. Programming information can be found in the manuals located on our website.

Step 3 - Verifying output from the speed control to motor.

Take voltage readings using the chart below. First readings should be with the FSC set to 50% and then a second reading should be taken when FSC is set to 100%. Voltage should change from 12VDC to 24VDC. For Nidec motors, make sure the plug is connected properly on the back of the controller. See detail picture in chart below.
If the voltages do not change, or you do not have no DC voltage output and you have double checked all the settings, replace the FSC.

Example motor part numbers below.

Highlighted text indicates 42 or 48.

FSC set to 100%

+ lead on red wire / - lead on yellow wire

23.8V DC

Voltage should be 24V DC +/- 10%.

FSC set to 50%

+ lead on red wire / - lead on yellow wire

12V DC

Voltage should be 12V DC +/- 10%.

With speed control illuminated and speed set to 50%, measure the DC voltage across the pins indicated in the below picture. The voltage at 50% should be 12V DC. Care should be taken with meter leads as to not damage the pins. If DC voltage is correct at 50%, adjust the speed to 100% and the voltage should be 24V DC. If voltages are tested and correct at the speed control, inspect the wiring harness. 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.