A simple Arduino sketch using a temperature sensor such as the DS18B20 would be able to detect the temperature and then do something (even via relay) but how do you expect the compressors to be switched off?
I don't think you can just cut off the power, it's not good for them. Have they got a mechanism you can use to turn them off (I think they continue to run for at least 30 seconds after such a request for operational reasons).