This includes air conditioners, heat pumps, and furnaces. ECM Motors can adjust the airflow depending on what the system is getting for feedback.
If the motor fails, it can simply be replaced. If the control module fails, it needs the chip to be programmed for the unit.
Basics Steps to Locate the Problem with an ECM Motor
- Set the thermostat to Blower, which should send 24 volts to G (blower) and C (Common) terminals.
- Use a multi-meter and verify 24 volts DC is being supplied at the thermostat G (Blower) and C (Common) terminals.)
- Use a multi-meter and verify the motor is getting power. (There should be a high voltage of 115 volts or 220 volts.)
- Power the unit off at the breaker or pull the disconnect so the system has no power.
- Separate the control module from the motor.
- The three wires which go into the motor should be tested for resistance from one to the other.
- Test for resistance to see of the motor windings are good, and each resistance value should be close to the other within 10 percent.
- Also, check each leg of the motor wires to the case to see if one has shorted out.
- If the values are wrong, then the motor is bad.
- If the values are correct and the motor spins well, then the ECM is likely bad.
The above are the basic steps to help narrow down a problem on suspected bad ECM motor.
There are more tests that can be done, including with the right diagram for your motor jumping the harness to get the motor to run.
More than likely, it will be a bad motor, as in my experience this is the most common failure, and it will need to be replaced.
The ECM control modules fail also, so be sure to verify it has gone bad.
Remember, the control module is programmed to work with that unit, so it must go back on a new motor.
There is a common failure on ECM motors with the thermister going bad. Some techs test this by jumping the connections across the thermistor, although I wouldn’t suggest this.
Control modules should be bought from the manufacturer. Remember, a 2.3 module from Rheem cannot be used on a 2.3 motor for a Trane system even if they look the same.
There are many problems that an ECM motor can have. Sometimes it is simply a pin on a Molex connector that needs to be pushed in; other times, the entire unit can be bad.
Caution must be taken when dealing with any HVAC system as there is high voltage in any system. Do not attempt to repair a unit yourself unless you have had training in proper high voltage practices and safety.