If the compressor is running all the time it may be short of refrigerant, look to the rear, look for type of refrigerant, if it is a propane (Klea**) you may have a problem geting it serviced, if it has a HCFC R132a should be no problem.
If it says R12, you will require the council to collect it has it is unservicable, (CFC R12 is now a banned substance)
You have one of two problems either short of refrigerant or the sensor is cutting out early in which case you should notice the compressor switch off, in the former case you will require a qualified refrigeration engineer, (ask to see his 2078 certificate)
PJW
February 2006