Abstract: A device for sensing pressure and temperature within the crankcase of a refrigerant compressor is adapted to protectively stop the operation of the compressor when temperature and pressure conditions within the crankcase permit existence therein of liquid refrigerant. The device utilizes a sealed vessel containing liquid refrigerant. The sealed vessel extends from a head portion downwardly into the crankcase fluid, and is provided with a pressure-displaceable membrane seal in the head portion. When the membrane expands due to high temperature within the crankcase, it causes closure of an electrical circuit. A pressure equalizing conduit equalizes the pressure between the crankcase and a chamber that surrounds said head portion.