T901_O: Inverter Fault - Compressor Overcurrent
On the VSODC, this fault would be displayed on the seven-segment LED as a number 15. Keep in mind, a 15 on the VSODC doesn't not exclusively mean it is a T901_O fault. You will need to confirm this at the EcoNet Thermostat or by checking the flashing Red or Yellow LED's in the upper right quadrant of the drive itself.
The Drive LED's will be flashing either 1 or 3 yellows, or 4 red flashes.
This fault occurs when the drive detects high current when trying to start.
This could be a compressor that is either hydraulically locked with liquid or oil in the scrolls as a result of off cycle migration, being considerably overcharged, or internally damaged and seized. The compressor may also be grounded. A grounded compressor in one of these systems will unlikely trip the breaker, but rather throw a, overcurrent alarm
The quickest way to find the problem is to perform the following diagnostic steps in the order below:
1. Shut off power to the ODU and IDU. Wait at least 1 minute for the Inverter Board LED indicators to turn off to ensure the drive capacitors have discharged. Disconnect the compressor wires from the Inverter Board W, V, and U terminals. Check for a grounded motor. If the motor checks out OK then continue on to the next step.
2. Install a belly band type crankcase heater 1” off the bottom of the compressor shell. Energize it with line voltage. Watch for sweating or frosting on the compressor shell. This would indicate liquid refrigerant is being boiled off. When the sweating/frosting stops, call for operation and see if the compressor starts. If it does, the charge and indoor air volume should be checked. If no sweating or frosting occurs, go to the next step.
3. With Power OFF and the Inverter Board LED indicators OFF, allow the drive capacitors time to discharge, and try and reverse the rotation of the compressor to see if it will start backwards. If it does, only run the compressor briefly. To reverse the rotation of the compressor, switch two of the wire positions on the W, V and U terminals of the inverter board. This will cause the compressor to reverse direction if it can run. Turn on power and call for operation.
4. If the compressor runs (may be noisy), shut off power, and allow the Inverter board time to discharge. Re-connect in the proper order and see if the compressor will run. If the compressor doesn’t run, replace the compressor. If the compressor runs, check the system charge for gross overcharging.
