1993 Cadillac STS Oil and Air Conditioning Problems

I just replaced the oil pump on my Cadillac STS and its still not pumping oil to the engine. It did at first but now its not. It sounds like a diesel engine now. Also, I just put on a compressor for the air and the Freon tank is empty but I can still smell the Freon coming in the car even though the air unit is off. Someone said it might be the coil located between the frame and dash is that a possibility. The info system always reads low oil pressure and Battery High Voltage. Need Help before looking to buy a engine to replace this one.