Control method of cooling system

A control method for a cooling system including a vehicle operation state detecting portion, the control method comprising:

• determining, by the controller, whether an output signal of an ambient temperature sensor of the vehicle operation state detecting portion configured to detect a temperature of ambient air satisfies a predetermined ambient low temperature driving condition;
• determining, by the controller, whether an output signal of a first coolant temperature sensor of the vehicle operation state detecting portion, configured to detect a temperature of coolant flowing through a cylinder head, satisfies a predetermined first low temperature driving condition when the output signal of the ambient temperature sensor satisfies the predetermined the ambient low temperature driving condition;
• and
• operating, by the controller, a coolant control valve unit configured to receive coolant from the cylinder head to open a first coolant passage and a third coolant passage and to close a second coolant passage when the output signal of the first coolant temperature sensor satisfies the predetermined first low temperature driving condition,
• wherein the first coolant passage communicates with a heater, the second coolant passage communicates with a radiator, and the third coolant passage communicates with an engine block,
• wherein the predetermined ambient low temperature driving condition is satisfied when the temperature of ambient air is less than a predetermined ambient low temperature, and
• wherein the predetermined first low temperature driving condition is satisfied when the temperature of the coolant passing through the cylinder head is less than a first threshold temperature.