You might suspect your air conditioner needs refrigerant if you notice the following signs:
Reduced Cooling:  The unit struggles to cool your home effectively.
Longer Cooling Times:  Takes longer than usual to reach the set temperature.
Ice on Coils:  Ice formation on the refrigerant lines or evaporator coils.
Hissing or Bubbling Noises:  Indicates a possible refrigerant leak.
High Energy Bills:  Inefficiency due to low refrigerant levels can lead to increased energy consumption.
Warm Air from Vents:  Even when set to cool, the air blown is warm.