Cadillac Repair: 199 cadillac, runnig, blower motor

Question
Can you please tell me why my emission light keeps coming on and when I have the a/c runnig and stop the engine the a/c is still running -so I have to start the engine back up and then turn the engine off.  

Answer
Hi Terry, I need to know the year and model caddy before I can give you an answer. Also do you mean the blower motor continues to run with the key out of the ignition because the a/c compressor can't turn or run unless the engine is running. Thanks, Bill