In some cases, when your indoor unit has an air conditioner leak, the unpleasant smell of toxic freon gas can quickly become apparent. However, you may want to check your outdoor compressor set for this smell.
Remember to also check the pipes and look out for some stains, as this could also be a sign of a leaking air conditioner gas line. Finally, you can also check the thermostatic expansion valve for whistling noises, which indicate low refrigerant levels.