Degradation sensing and shut-down means for refrigeration motor-compressor units

In an enclosed motor-compressor unit for air conditioning or heat pump service which includes an accumulation of refrigerant-oil mixture in the enclosure, an A.C. electrical power source, circuit connections including a normally closed switch connecting the motor of said unit across said A.C. power source, a relay which when energized opens said normally closed switch thereby to shut-down operation of said unit, means for continuously energizing said relay when contamination of said mixture by conductive particles therein attains a predetermined degree comprising:

• a source of D.C. electrical power, a silicon controlled rectifier, circuit connections connecting said silicon controlled rectifier and said relay in series across said D.C. power source, a contaminant sensor comprising a pair of spaced electrodes immersed in said mixture, a capacitor, circuit connections connecting said electrodes and said capacitor in series across said D.C. power source, and voltage responsive means for turning on said silicon controlled rectifier when a predetermined charge is attained on said capacitor.