Is the compressor air-cooled or water-cooled?
If it's water-cooled, is there water in the cooling system? are the jacket passages and heat exchangers all gunked up? Is the water pump working? Is there are fan on the heat exchanger? Is it working?
If it's air-cooled, is the compressor installed in an enclosure or small room where there is no flow of cooling air?
Is there an oil cooler? Same questions as above apply for it.