A stabiliser measures incoming voltage and adjusts it using a transformer with taps switched by relays, or a motor-driven servo. If the supply falls to, say, 190 V, the stabiliser boosts it closer to 230 V; if it rises too high, it bucks it down. Most also cut off output if voltage goes outside their correction range.
For refrigeration, two features matter. First, an adequate rating for the compressor's starting current, not only its running load. Second, a time-delay on start-up, typically a few minutes after power returns. This delay lets refrigerant pressures equalise so the compressor does not try to restart against high pressure, which is a common cause of locked-rotor trips and burnt windings after power cuts.
Many modern compressors and inverter drives tolerate a wider voltage range than older designs, so a stabiliser is not always required. Check the unit's rated voltage range and measure your site's real supply at peak and off-peak times. Where supply is regularly outside that range, a suitable stabiliser is cheap insurance compared with a compressor.