Without a working compressor, refrigerators won't stay cold. The compressor is a type of pump that uses pistons to compress the refrigerant--the gas that chills the inside of the refrigerator. When this pump stops working, the refrigerant does too. Depending on the cause of the problem, fixing a compressor can be relatively inexpensive or quite costly.

The condenser is another important part of any refrigerator. This unit removes heat from the condensed refrigerant, allowing it to expand and liquefy again before passing into the compressor. When dirt and dust build up on the condenser, it can overload the compressor, causing it to cut off every few minutes. This problem can look like a faulty compressor, but is easily solved for free by dusting the coils and condenser at the back of the refrigerator.

The start relay is an electronic device that tells the compressor when to start. When this switch goes bad, the compressor won't work properly. It may begin to make clicking noises about 2 to 5 minutes apart--a sign that the compressor is overheating. According to Refrigeration Basics, consumer appliance repair guide, replacing a bad start relay costs around £16.

Some refrigerators may have compressors insufficient to provide the cooling power they need, whether from poor design, age or another problem. Compressors with insufficient power tend to run continuously, but provide little to no cooling. According to All About Home (see reference 3), replacing the compressor with a more effective one costs between £325 and £455, before tax. In some cases, this cost may be higher than the value of the refrigerator.

Refrigerator compressors may also fail completely. In these cases, the refrigerator light should function correctly, but the refrigerator itself does not run. As with an insufficient compressor, replacement costs tend to run £325 to £455. Repairing the compressor is difficult and is not usually cost-effective.