Thermostatic expansion valve with electronic controller

DETAILED DESCRIPTION Referring now to FIG.
1, the control system of the present invention, indicated generally at 10, has a refrigerant compressor 12 coupled by means of electric clutch 14 to a drive pulley 16 driven by belt 18 connected to a source of power, as for example the engine of an automotive vehicle.
High pressure gaseous refrigerant is discharged from the compressor through conduit 20 to the condenser indicated generally at 22 which is cooled by fan 24 driven by fan motor 26.
Cooled liquid refrigerant discharges from the condenser through conduit 28 to the inlet of the expansion means such as the thermal expansion valve indicated generally at 30.
The low pressure discharge of the thermal expansion valve 30 is discharged at the outlet thereof through conduit 32 to the inlet of an evaporator indicated generally at 34, which absorbs heat from the surrounding air such as in the passenger compartment of a vehicle for providing passenger comfort therein.
Evaporator 34 discharges through conduit 36 and through return passage 38 formed through the body 31 of expansion valve 30 and through conduit 40 to the compressor suction inlet.
A self-heated thermistor 42 is disposed in the high pressure line 28, and preferably in valve body 31 at the inlet thereof, for refrigerant flow thereover.
The thermistor receives a voltage from junction 52 through resistor R24 which is connected through lead 50 to self heat control 54.
In the presently preferred practice the self-heated thermistor 42 is an NTC thermistor manufactured by Fenwall Electronics, 63 Fountain Street, Farmingham, Mass.
01701 bearing manufacturer's identification FD21J1-W, and has a resistance of 100 OHMS at 25 degrees C.
Junction 52 is also connected through lead 60 to one input of a comparator 62 which is controlled by the microcomputer of microprocessor based controller 64, which is powered by a suitable power supply including voltage regulator network 44.
A drive signal is provided along lead 66 from controller 64 to fan relay 68 which controls the fan motor 26 along lead 70