32 at the end of the non orbiting scroll wrap 20 has just sealed a compression chamber 33 which extends around to approximately point a a similar outward radial tip 34 at the end of wrap 22 has just sealed against wrap 20 fig2 shows the scroll assembly 180 u00b0 crank angle later wherein the inner tip 36 of orbiting scroll wrap 22 is ready to separate from wrap 20 and place fluid in compression chamber 31 in communication with discharge opening 26 the beginning of chamber 31 being indicated at point b the outward radial tips 32 and 34 allow a new charge of refrigerant to be received in compressor assembly 14 further orbiting of scroll member 18 will cause continuing discharge in the usual manner in accordance with this invention a unique arrangement is provided for sensing an internal chamber pressure in scroll machine and depending on the application disabling the driving motor so that the compressor cannot be operated if the pressure indication is above or below a predetermined value in this regard either absolute chamber pressure or the differential between the chamber pressure and suction pressure can be sensed referring to the drawings a pressure sensing port 40 is located in end plate 17 in a position to sense the pressure in chamber 30 port 40 is preferably located just inwardly of point a because that is where the maximum vacuum will be developed in a reverse rotation situation and yet is a point which will never see suction pressure port 40 can be located further angularly inwardly if desired such as to increase response time but cannot be located.