my AC unit doesn't blow cold air

You can't expect the problem to be anything. ONLY proper diagnosis will tell you what it is. EXPECT to pay for probably an hours labor plus materials to evacuate and recharge the system with dye and check for leaks , or other cause of failure. By not using the proper equipment to add refrigerant you may still just have the incorrect amount in it.

Agree with answer #1..

My AC has never blown cold air since I bought it. I have a 2010 with 56,xxx. Never in my life have I been able to turn the fan on high, set the temp as low as it can go, for longer than a minute or two. Well now I can last for 30 minutes at a time. I paid for more freon at one point and that didn't help. They checked for leaks and found nothing. Just one more problem I have had with this car....