What can cause a dripping water out from the air-conditioner on the wall ?

OMG, it is so hot today here and our air-conditioner start to drip water from his plastic outside. It is working fine, refrigerate fine.

I have cleaned it well, I checked he was not full of dust, but after several days of good work he started to drizzle again. Is it possible that something is frozen in his pipe?

Any idea what to check or clean or do?