Can't diagnose it over a computer; if we could, we wouldn't need mechanics. What I CAN suggest is the first thing is you have to determine where that grinding noise is coming from. Is it under the hood from the AC compressor? If so, it will only occur with the engine running and you may hear it cycle on and off. If it occurs from inside the car, that is likely the heater / AC fan. That can run without running the engine.
If the heater fan doesn't run on all speeds, that is usually caused by a bad resistor assembly or fan speed switch. In the last 15 years or so the engineers have added a very unreliable computer to do things computers were never needed for before. As a result, it is common to have all kinds of new and unusual problems caused by those computers.
The place to start is by returning to the shop the did the AC work to allow them to recheck their work. You do not have the entire AC system replaced. You have defective parts in the system replaced, and one of the new parts could be defective or there could be some other problem the mechanic didn't see earlier.
Wednesday, July 11th, 2012 AT 6:52 PM