LG Inverter Air Conditioner showing CH 02 what can I do?

The model number would be on the right hand side of the outdoor unit and same on the indoor unit if it is a midwall split. If it is a flat cassette cieling type you may need to open the grill, which is simply two little levers either side of the grill, and the grill will swing open. Without the model number it is difficult to give accurate info. However, I can offer the following. One, check the condensate drain. You can just blow into the drain pipe from the outside and this sometimes clears clogged mud in the drainpan. Or two, error reading can also come from phase failure (in the case of a three phase unit) or power related problem. This can be solved by switching off the mains and then switching on again to reset. If you have a phase failure you would need an electrician to confirm that the power supply is good. Unless you have a volt meter.