My a/c is not working--the compressor is kicking in than off and no air--is there a sensor to change---1993 Cadillac Deville it is also full of freon

check freon and pressure with gauges - bet its low

Your system may still low on refrigerant charge. Most low pressure switches are preset to cut out (open) and cut off the compressor at about 25 psi for an R-134A system> You will need guages to determine this. If this system has not been properly serviced in the past, the individual that charge it may have gotten air and non-condensibles in the refrigeration system. The high pressure guage is the only way to determine this (if so you will see the head pressure normally go above 350 psi very rapidly (If so get a qualified service technician to service your system, it will have to be evacuated and recharged).
When charging the system, you will be connected to the suction side (low pressure side) and it should be charged as a vapor to prevent liquid flood back to the compressor, liquid can result in mechanical failure. As you add charge to the system have the car doors and windows closed, the temperature controls set to max A/C and the temp to the lowest setting with fan on high. Charge system slowly (holding your hand on the suction line, The Large line going back to the compressor) until you start feeling cool to cold temperature drop on the line. At that time stop charging and allow the car interior to cool off... you should have a full charge and the short cycling of the compressor should have stopped. Be sure to verify the type of refrigerant required for this system, due to the year of the car it may have a refrigerant 12 charge vice the currently used refrigerant 134A. They cannot be mixed!

If your system is low on freon (and that's my diagnosis as well) then you have a leak somewhere. you have to have the leak fixed or you'll continue to go through this. If you're not a certified tech don't attempt a/c repairs yourself. Have the system checked for leaks and once it's found have it repaired before evacuating and charging the system.