If you notice the following signs, your system may be failing;
AC starts blowing warm air instead of cold air.
It takes several minutes to turn on.
A large pool of condensation or refrigerant leaks around the outdoor unit.
Illegal burning and clammy odors are coming from the unit.
Suppose the number of repairs is increasing and getting expensive with time. The unit constantly turns on and off without rest. It is called short cycling.
A sudden spike in your energy bills compared to previous months.