Thank you both respondents. I didn't realize the can itself would remain at about 60 psi until it was nearly empty. This in itself explains how it can overcome the low side pressure until it is in fact empty. I just assumed it was a linear decline in pressure inside the can.

I have what might seem like an odd question but one that has puzzled me for many years. I know that when charging a system with guages a freon can will empty into the low side. It may take a while, but eventually the can of freon will empty into the low side given the system has some charge and the ...