LG and C5 fault codes occur when there is lack of communication between the indoor and outdoor units. Most likely, the wire connecting the units is damaged, or there is a problem in the control board. Please, check all wires and connections between the units. If the problem persists, use  professional technical help. You may see the following indications:
LG AC Fault Definition: poor contact between indoor and outdoor units
- Flashing Light (5)
- Display (Indoor Outdoor)
- Indoor Operation (OFF)