I just bought preowned 2008 C300 Sport and the AC would first come on and off but now it will not come on at all. The heat works fine. I tried manually and also on auto and both ways it will not come on. Can anyone tell me if it could be the fan blower regulator if so where is it located?

 

I just went and tried banging on the passenger side underneath the dashboard. The blower fan came on very slowly with a rattling sound and then it stops. Is it the fan blower or the fan blower regulator??