It's your car compressor that supplies the power to in car AC system as well as pressurising and circulating the heated refrigerant vapor.
Usually resembling a pump with large rubber and steel hoses, there are a number of potential car compressor faults that might affect its performance and leave you hot and bothered are - The compressor clutch might not be engaging or there could be a bad fuse, wiring problem, compressors generally fail due to contaminates entering the compressor or due to lack of oil; its vital that the correct PAG oil is used when replacing the compressor.