AC not blowing cold in afternoon

Please provide a little more information.
What is the weather like?
Is the vehicle running all day?
Is it not blowing cold after sitting all day in the hot sun?
Have you checked to make sure that the electric suplimental fan is running while the a/c is turned on?

How does the guage read at different outside temp?

It tould possibly be the dryer, but if it blows cold in the mornings its less likely that, and more likely a charge/mechanical cooling problem.