Q: What do I do if the screen displays "OFF (AC Out S-C)" or "E: AC Out Short-C" (Error E4)?

Step 1: Check for External Switches. Ensure there are no breakers or switches installed between the inverter and the pump, as these cause this error. Remove any such devices immediately.
Step 2: Perform a Resistance Test. This identifies internal shorts in the motor or cable. Turn off the inverter and isolate all power sources (solar, mains, or generator). Wait for the screen to turn off completely and then unplug the AC output plug or disconnect the wires from the U, V, W, and Earth terminals.
- For Three-Phase: Measure resistance between U-V, V-W, and U-W; all three readings must be identical. If any reading differs by more than 1 Ohm, the motor or cable is faulty.
- For Single-Phase: Measure all three pairs; the sum of the two lowest readings must equal the highest reading (e.g., if V-W is 3.2 and W-U is 5.3, U-V must be 8.5). If they differ by more than 1 Ohm, a fault exists.
Step 3: Test the Inverter Without Load. With the pump still unplugged, turn the inverter back on. Check the "AC Output Status" on the screen; if the frequency reaches the maximum set value (usually 50Hz), the inverter is healthy, and the short is definitely in the pump or cable.
Step 4: Inspect Plugs. Look for black marks on the male and female AC output plugs. If marks are found, the connection has been shorting, and the MC4 plugs must be replaced.