I'm a new owner and my a/c is not functioning well. It only begins to cool while I'm driving.

vwpassat07k

When I approach a stop my a/c stops working and then begins working again when I drive. How can I fix this problem? 

elias

a contributor could be a slipping belt. has belt been serviced on schedule? is it squeaky and/or glazed? aside from that it will requires proper AC system service starting with measuring all intake/output temperatures and refrigerant pressures.