Here is some information to help solve the issue.
E2 error code indicates an abnormal voltage and frequency fluctuation. This can be related to a wrong wire size or a wrong breaker size. If the unit is connected with the appropriate wire sizes, your circuit boards might be faulty. You can perform the following test:
To test your indoor and outdoor circuit board,
you will simply have to verify the voltage frequency using a digital multi-meter. You will have to set your device on DC (direct current) and verify the voltage fluctuation between terminals L2-S or for some models it would be between 2 and 3 on the outdoor terminal block. The result should be fluctuating between -50 and +50 VDC alternatively. If the the voltage fluctuates with only positive or only negative numbers, this indicates that outdoor mother board will have to be replaced. If the result remains constant and there is no fluctuation at all, the indoor board will have to be replaced