The air conditioning hot air of Doosan excavator relies on the excess heat brought by the engine water cooling system, so besides the air conditioning control switch in the cab, there are water pipe valves near the engine. Generally, in summer, the valve of the water pipe will be closed for fear of affecting the air conditioning and refrigeration.
It's also very simple to find. The valve is not on the water tank, near the engine, but between the engine and the fan. It looks a bit like a faucet-shaped valve. Only the water valve is like that, close to the whole engine, very easy to find.