In my last 2 posts, we discussed how to use your meters to check out ECM motors, modules, and control boards. These checks involved taking voltage reading and resistance reading on the various components to see where the problem occurred that caused the motor not to run.
But, did you know that there are “diagnostic” tools out there that make this a lot easier? Well, there are!
ECM motor controls can also be checked with the TECMate™ Service Tool.
The switch should be placed in the “ON” position and the LED light on the switch should illuminate when connected properly to 24 VAC. The motor should be observed for 15 seconds. The Table on the back of the TECMate PRO™ can be referred to for operation guidelines.
If the motor starts with the TECMate™ the system malfunction is not caused by an ECM module or motor problem.
1) When finished testing with the TECMate™, place the switch(s) in the “OFF” position on the TECMate™ and wait for the motor to completely stop. Depending on the program, sometimes the motor will not shut off immediately after a test; this is normal.
2) Once the motor comes to a complete stop, turn the system power off before removing the TECMate™. The 16-pin connector must be reconnected to the system before proceeding with the diagnosis. The connector is keyed and has one clip that should click when the connector is inserted properly.
3) The next step is to check the low voltage communication on the 16-pin connector as discussed in my last post. If control voltage is not present, the problem is most likely the communication from the control board or the communication through the 16-pin connector or harness.
The connections at both ends of the 16 pin connector and the wires to the connector should be evaluated for damage. The sockets must not be distorted, bent or pushed out of the connector.
If the motor does not start with the TECMate™, the electronic control (motor control) should be replaced. BUT — before replacing the electronic control module, test the motor to ensure it is not also damaged. Procedures for testing the motor are included in my previous post.
Final Installation Checks – ECM motors
A visual inspection of all wiring and connections, especially those removed while servicing should be completed.
The system should be setup as follows:
- The AC power should be reconnected to the HVAC system and verification that the new motor control module is working properly should be completed.
- All leaks in return ducts and equipment cabinet should be plugged and sealed by approved methods.
- Verify that the system is running quietly and smoothly, in all modes (heating, cooling, and continuous fan) and all stages (if applicable).
- The thermostat settings should be returned to the customers preference.
If this is a repeat failure, check the following:
- Any evidence of moisture requires correcting the issue.
- be sure there is an adequate drip loop in the wiring harness.
- If the area is subject to high amounts of lightning strikes, the use of additional transient protection may be helpful.
- If the unit is not already equipped with a “choke coil”, you may want to add this to the system (see older post on choke coils).
The nice thing about diagnosing with the TECMate™ is that it tells you right away if the motor/module is defective so you can concentrate on the harness / board side of your system if the motor runs. If the motor does not run, it is probably a defective module but, you will still need to do the diagnostics in the previous post for the motor resistance checks before replacing just the control module. You may need to also replace the motor.
On most equipment today, the module and motor can be obtained as separate components. Modules do need to be programmed for the specific manufacturer’s model and are not interchangeable either in the individual brand or across brands. There is no universal program for ECM motors so be sure to get the correctly programmed module for your application.
I hope these last few posts have helped you in diagnosing ECM motors. with the demand for higher efficiency equipment and components, ECM motors are becoming more common is HVAC systems and the need for proper diagnosis is becoming ever more a requirement for the technician working on the higher efficiency equipment.