If you need more than 2-14oz cans you probably have a leak. O rings at the hose connections can be replaced for $10 by buying a set. A vaccumn pump must be used if system is di-connected at Harbor Freight for $14.Dye can be added with freon to see a leak. Freon sniffers can also be had for $80. http://www.autoacforum.com/messageview.cfm?catid=20&threadid=9172 best site for "flushing a system." if you dont wanna replace ALL of the parts