Hi. I was driving my 2010 Audi Q7 4.2tdi and when I tried to turn off the rear A.C is stopped cooling. I got it checked at a local mechanic. There was no error shown in the scan. Power supply is ok and Gas in tact(no leakage). Can anyone suggest what could be the problem? The mechanic said that whole A.C unit will be changed but I have a feeling that the fault is not that big.