Technically, the E4 error is not an error at all. It actually tells you, your unit is going into defrost mode. That does, however, mean that something has caused your unit to get too cold. A broken temperature sensor can also cause your AC to enter defrost mode.

Error code e320 indicates an OLP sensor issue. The sensor is located in the outdoor unit. First, you can try to reset it by switching it off for 30 seconds or so. If the error appears again, the temperature sensor is faulty and will need to be replaced.