Coolant/refrigerant temperature control system

A coolant/refrigerant temperature control system for controlling the temperature of coolant flowing through the coolant radiator of an internal combustion engine in a vehicle and for also controlling the temperature of refrigerant flowing through the condenser of an air conditioning system for the vehicle thereby to control the refrigerant discharge pressure, the condenser being mounted in front of the radiator, said temperature control system comprising:

• temperature sensing means for sensing the coolant temperature and producing a temperature signal having an amplitude proportional to the sensed coolant temperature;
• a pulse width modulation circuit for developing, in response to said temperature signal, a pulse width modulated signal having a duty cycle which is proportional to the sensed coolant temperature;
• means responsive to said pulse width modulated signal for producing a controlled fluid pressure which is a function of and represents the sensed coolant temperature;
• a variable speed fan drive, controlled by the fluid pressure, for normally blowing a controlled amount of air through the condenser, to dissipate heat absorbed by the refrigerant, and then through the radiator, to dissipate heat absorbed by the coolant, as determined by the sensed coolant temperature;
• pressure sensing means for sensing the compressor discharge pressure of the refrigerant in the air conditioning system, which discharge pressure is directly proportional to the refrigerant temperature in the condenser;
• and an override circuit, responsive to said pressure sensing means when the sensed discharge pressure exceeds a predetermined maximum allowable level, for overriding the operation of the pulse width modulation circuit to change the fluid pressure as necessary to maximize the fan speed and thus the air pulled in through the condenser and radiator, thereby reducing the refrigerant temperature in the condenser and consequently the refrigerant discharge pressure.