You should have your system serviced. It sounds like your compressor is bad. Mine was doing the same thing and I found out it was a burnt up compressor.
There are a few reasons why a central air unit is not blowing cold air. The coils may be dirty, the unit may need freon, or the thermostat could be broken.
Check the temperature control cable
sounds like your freon may be low
you may be low on freon and jsut need a good charge of R134a
Freon is too low, or too high.
Look to see if the compressor is running when the ac is on. If not, then check the Freon pressure, as the compressor won't run if the Freon is low.
As the Freon level in your air conditioning system gets lower the cold air will become warmer and warmer. You will need to recharge the system with Freon.
low on freon
Could be many reasons but the most common would be low on freon due to a leak in the system.
How do you know it is charged properly? If you did not put gauges on the system? If no air is coming thru the vents the coil may be clogged. This list could take a long time!!
Blown fuse? Freon leak? Suggest you take it and have it checked to be sure.
Check to see if the ac compressor is running. If it is not, use a gauge to check the Freon levels, as low Freon is the most common cause of no cold air blowing.