The Highway Fuel Economy Test (HwFET) was run on a 2002 Ford Escort with 70,480 miles. The Escort had a fixed displacement A/C compressor. 

THE RESULTS: A HALF A MILE PER GALLON increase in fuel economy! The the average vehicle getting 20 miles per gallon, driving 15,000 miles a year and paying $2.50 a gallon for gas will SAVE $45.

Download a copy of the report here (PDF format)