Honda ac system

i have a 2001 honda civic. When i turn on the car my ac works fine the air is cold but after a while the air gets hot. i thought it needed coolant so i got a few cans and the hose with a presure gauge that shows blue for low green for good and red for over fill. when i tried to fill the ac system the gauge whent to green so i did not add any more coolent. what could be the problem? could it still need more coolant?

The problem is that you need to take the car to an air conditioning technician for a true diagnosis.

…and it was refrigerant in the can, not coolant.