The reason for a compressor being stuck-up is usually the result of moisture in the system, or a lack of lubrication. When this occurs, the compressor should be thoroughly cleaned out. The compressor should be completely disassembled and the parts thoroughly cleaned and refitted. New oil and refrigerant should be put into the cleaned system. A tight compressor will result when a cylinder head, seal cover, or similar part has been removed and not replaced carefully, or when the screws have been tightened unevenly.