A/C problem I need help

The air conditioning button on my console continues to blink and the AC does not work at all. The air blows out the vents, but other than that it is totally non functional. I checked the relay by putting it in a friends vehicle and it works so I have no idea what the problem is. Can anyone help me out?

 

I'll start with the obvious, have you checked the refrig. level? Does the A/C pump cycle? I had a leak and didn't know about it, and when diagnosing things I realized the pump never turned on and had no refrigerant. The system still leaks but if I put a can of 134 in every couple months things are fine.