The common problem lies with the resistor packs that burn out, however this isn't the case with you as your blower works on all speeds, it sounds as if the air ducts may be blocked up with debris such as leaves etc, is it left under a tree?

Is it better in other directions, I.E footwell or screen?

The A/C almost certainly needs regassing, the light will still come on but it won't actually work, there is a pressure switch built into the system, when the pressure drops it stops the A/C from working to stop any damage, you will also find the cooling fans do not work when switched on either which they should do.

Martin