There are many things that can cause your AC unit to stop working correctly. Here are some tips on AC Repair.
The easiest problem to spot is a bad capacitor. If this is broken the fan works but will blow out warm or hot air instead of cold air.
There may also be a buzzing sound every 30 seconds. In this case, you would replace the capacitor to fix the problem. You should look at your AC unit manual to confirm the type of capacitor you need.
AC units can lose refrigerant. If that happens the refrigerant should be replaced. This may be the problem if the AC unit can't quite reach the desired temperature.
If the AC unit is working slightly less efficiently you can try replacing or cleaning the filter. Cleaning or even replacing the filter is easy and the unit is usually designed to allow anyone to do this kind of maintenance. If you need to completely replace the filter you should confirm the exact filter type and size in the product's manual.
A working AC unit with a big puddle of water under it could indicate that there is a plugged pip or hose.
For more tips see the linked video..