Question: I keep getting a low voltage error code (75) and I checked the supply with a meter and the power is just fine. Any suggestions?
Answer: Open up the faceplate and see if the green molex power plug is securely pushed in. Sometimes the low voltage error code is caused because of wire instead of the recommended stranded wire.
When the faceplate is closed, the hard wire pulls the module down just enough to power the VFD not enough to run the motor at the proper voltage required. Be sure to see that the plug is pushed in tight and be careful when re-installing the faceplate.
If that does not work, check to see if it was piped with check valves on the discharge per the instructions. Occasionally the pump that is not enabled to run acts like a generator powering the motor through backflow just enough to run but no enough to satisfy the electrical requirements causing a low voltage alarm. Once the check valves are installed, the issue should go away.
If the problem persists, contact your local Grundfos wholesaler for assistance.