Electric Motor Testing and Troubleshooting: Variable Speed Motors
IF THE MOTOR IS RUNNING:
- It is normal for the motor to rock back and forth on start up. Do not replace the motor if this is the only symptom identified.
- If the system is excessively noisy, does not appear to change speeds in response to a demand (Heat or Cool), or is having symptoms during the cycle such as a tripping limit or freezing coil, check the following:
- Wait for programmed delays to time out. If delays are too long, then reset them using the manufacturer’s charts.
- Ensure the airflow settings are correct for the installed system using the manufacturer’s charts. Remember that the change in airflow between continuous-fan speed and low stages of operation may be very slight depending on the size of the system. If the system is operating normally in each stage, then there is no problem.
- Remove the filter and check that all of the dampers, registers, and grills are open and free flowing. If removing the filter corrects the problem, clean or replace with a less restrictive filter. Also check and clean as needed the blower wheel, secondary heat exchanger (if applicable) and evaporator coil (if applicable).
- If this does not correct the problem then check the external static pressure. If it is higher than the manufacturer’s recommendations, correct the airflow restriction.
- If the motor does not shut off at the end of the cycle, check the delay times and wait for the delays to time out. Also, make sure that there is no call for “Continuous fan” on the “G” terminal. This motor may take a while to come to a complete stop with selected delays and the normal ramp down.
- If the 2.0 / 2.3 / Eon® / 3.0 motor has proper high voltage and ground at the 5-pin connector, go to the Troubleshooting with the TECINspect® Service Tool section below. If the 2.5 motor has proper high voltage and ground at the 5-pin connector, the equipment manufacturer’s checks, located in their service manuals, must be referenced. This guide cannot troubleshoot communication to the 2.5 motor. The TECINspect Service Tool is not designed for use on the 2.5 motor.
IF THE MOTOR IS NOT RUNNING:
- Check for proper high voltage and ground at the 5-pin connector at the motor. Correct any voltage issues before proceeding to the next step. These are dual voltage motors capable of operating in 120 or 240VAC systems. On 120VAC systems there should be a jumper between terminals 1 and 2 (see Figure 1). On 240VAC systems the jumper should be removed (see Figure 2). If a motor is operating at 240VAC with the jumper in place, the motor will be permanently damaged. Input voltage within plus or minus 10% of the nominal 120VAC or 240VAC is acceptable.
- If the 2.0 / 2.3 / Eon® / 3.0 motor has proper high voltage and ground at the 5-pin connector, go to the Troubleshooting with the TECINspect® Service Tool section below. If the 2.5 motor has proper high voltage and ground at the 5-pin connector, the equipment manufacturer’s checks, located in their service manuals, must be referenced. This guide cannot troubleshoot the communication to the 2.5 motor. The TECINspect Service Tool is not designed for use on the 2.5 motor.
- If further troubleshooting identifies a failed control module, go to the Replacing the ECM Control Module section below for replacement steps.
Troubleshooting with the TECINspect® Service Tool
For models 2.0 / 2.3 / Eon® / 3.0 only
The TECINspect Service Tool is capable of identifying a motor control failure versus another HVAC system controller or wiring failures. To test for motor control failure, follow these steps:
- Connect the TECINspect Service Tool to the communication plug on the motor.
- On Models 2.0 / 2.3 / Eon remove the 5-pin AC power connector first to make accessing the 16-pin communication connector locking tab easier. Remove the 16-pin connector from the motor, and connect the 16-pin connector from the TECINspect Service Tool to the motor. Reconnect the 5-pin AC power connector.
- On Model 3.0 remove the 4-pin connector from the motor (do not remove the 5-pin AC power connector). Connect the 4-pin connector from the TECINspect Service Tool to the motor. Use the 16-4 pin adaptor with early model TECMate tools.
- Connect the two alligator clips from the TECINspect® Service Tool to a constant 24VAC (24VAC terminal and Common terminal) source such as the transformer low-voltage terminals or terminal strip on the manufacturer’s control board (see Figure 3 below). These connections are not polarity sensitive.
- Place the TECINspect Service Tool switch(es) in the OFF position.
- Reconnect the AC power to the system. The green LED light on the TECINspect Service Tool should be on when connected properly to 24VAC. If the green LED light is not on, there is no power to the TECINspect Service Tool or the TECINspect Service Tool has failed. Do not continue until the green LED is on by correcting low voltage issue/ connections or replacing the TECINspect Service Tool.
- Refer to the table on the back of the TECINspect Service Tool for operation guidelines. Observe the motor for a minimum of 15 seconds.
- If using a TECMate XL on Models 2.0 / 2.3 / Eon®, make sure to set the switches according to the instructions on the back for each demand test to eliminate misdiagnosing the problem.
- If using a TECMate XL on Model 3.0, the only switch necessary to test the motor is the furthest switch to the right (labeled BK/PWM on the XL or DH on the Troubleshooter).
- When testing is finished, place the TECINspect® switch(es) in the OFF position and wait for the motor to completely stop. (Based on the manufacturer’s program, the motor may not shut off immediately after a test; this is normal).
- If the motor operates using TECINspect Service Tool, both the control module and the motor module are ok. The motor may operate at a reduced speed during the TECINspect test, this is normal. Turn off the power to the unit, remove the 16-pin or 4-pin communication harness from both the motor and the manufacturer’s control board. Perform a continuity check on each individual wire of the harness. Some manufacturers use a different style connector on the control board side of the harness. Follow the wires to be sure of checking the proper pins. Replace the communication harness if any wires fail the continuity check, if any of the pins are bent beyond repair or damaged and check the system operation again. If the harness is good or a new harness does not solve the problem, troubleshoot the communication out of the manufacturer’s control board with their troubleshooting guide. Always troubleshoot the communication at the motor end of the harness.
- If the motor does not operate with the TECINspect Service Tool, confirm high voltage is present before replacing the control module. Follow the next section on Replacing the ECM Control Module.
Replacing the ECM Control Module
Before replacing the electronic-control module, you must test the motor module to ensure it is also not damaged. Installing a new control on a failed motor will result in no operation, improper operation and/or potential failure of the new control. Procedures for testing the motor module are included below:
- Disconnect AC power from the HVAC system. Unplug the 16-pin or 4-pin communication connector and the 5-pin connector from the motor control.
- Remove the blower assembly from the HVAC system if needed.
- ONLY after the system AC power has been off for 5 minutes, remove the two (2) hex-head screws from the back of the control.
- Unplug the 3-pin connector from the inside of the control by squeezing the latch and gently pulling on the connector (see Figure 4). Now you’re ready to test the motor.
Motor Module Tests
The Winding Test
Set ohm meter to the highest possible setting and measure resistance between each of the three motor leads to the unpainted part of the end shield (or x-brace on model Eon® & 3.0). The motor passes the test if the meter indicates greater than 100k ohms.
The Phase-to-Phase Test
Set ohm meter to lowest possible setting and measure the motor phase to phase resistance by checking these combinations of the 3-pin motor connector with an ohm meter:
Lead 1 to lead 2
Lead 1 to lead 3
Lead 2 to lead 3
For the purpose of this test, either end of the 3-pin plug is lead 1. Resistance values should be less than 20 ohms and each of the three values should be the same (plus or minus 10%). If the measured resistance is outside of these parameters, the motor fails the test.
If the motor passes both of these tests and the shaft spins freely when rotated by hand, then the motor is ok and only the control must be replaced. Continue with replacing the ECM control module in step 5.
If the motor fails either of these tests or does not spin freely when rotated by hand, replace the motor and control module following the guidelines on page 24. Insert the 3-pin connector back into the new control module. A slight click will be heard when inserted properly. This connector is keyed for proper connection. Attach the new control module with the plug connections oriented down (see figure 7, page 23), insert the appropriate bolts and tighten. Due to model replacements, some motors may need to be rotated in their mount to orient the plug connectors properly. See below for model specific notes and/or follow any OEM instructions included with the new control. Model 2.0 & 2.3 - These models are no longer available and can only be replaced with an OEM Eon® kit that includes a motor adapter ring (see below).
Model Eon - This model can only be replaced with an OEM Eon motor.
Model 2.5 - This model is no longer in production. It can only be replaced with an OEM 3.0 kit that includes a 16-4 pin wiring adapter and a motor adapter ring.
Model 3.0 - This model can only be replaced with an OEM 3.0.
Reinstall the blower/motor assembly into the HVAC system by following the manufacturer’s guidelines. Plug the 16-pin or 4-pin communication connector and the 5-pin connector back into the motor. The connectors are keyed. Observe proper orientation. Be certain to form a drip loop so that water cannot enter the motor by draining down the cables (see Figure 7 below). Go to the Final Installation Checks section.
Indoor Motor Final Installation Checks
- Check all wiring and connections, especially those removed while servicing.
Ensure the system is set up as follows:
- Clear all condensate drain and traps.
- Check and plug leaks in return ducts and equipment cabinet.
- Verify that the system is running quietly and smoothly, producing proper air flow in all modes (heating, cooling, and continuous fan) and all stages (if applicable).
- Return all thermostat settings to the customer’s preference.
- If any evidence of moisture, then correct the issue.
- If the area is subject to high amounts of lightning strikes, then use of additional transient protection may be helpful.
Additional Good Practices:
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