A/C not working

My AC works but it takes a very long time to start working. In order to expedite the AC working I drive the car around, then I put it in park and rev the engine, then I turn off the car for like five seconds and after that I turn it on again and rev the engine again. When I do all that the air is still luke warm but when I start to drive it after I go through the process the air starts to get really really cold. It would be a huge help of you could tell me what I should be looking for to fix so I am not just buying and replacing parts that I do not need to.

P.S. The AC fan is only on when I turn on the AC but it does not stay on unless I do the whole process I just told you about or after I wait for it to cool down. But when the air is cold the fan stays on the whole time unless I turn off the AC.