Leaks Around the Unit
If this happens immediately turn off your unit to reduce damage. These leaks are caused by moisture from the evaporator coil and while the fluid is typically drained out of the system, something probably needs repair. You should first see if it's a dirty air filter for an easy DIY fix. If that doesn't work it may be an issue with your AC's drain system or refrigerant levels, in which case you should call a professional.
Emitting a Bad Odor
Known as dirty sock syndrome, a bad odor from your AC typically means there's a collection of mold/bacteria in your HVAC system. You should clean this from the unit, but in the future, installing a UV air purifier can help prevent further mold/bacteria growth.
Odd Sounds
Your AC can be making noise if there's a loose or disconnected part or a buildup of debris in your system. If there is ever a screaming noise coming from your system, turn off your AC immediately and call for a technician - this typically comes from a refrigerant leak which could damage your family's health.
Your Home is Humid
This is an indication that there's mold in your AC unit being spread around your house. This is dangerous to your family's health and you should call for a technician to visit immediately.
Thermostat Issues
Issues with the thermostat don't always indicate an issue with the AC, but it could mean that your unit is having a hard time turning on or off.
Warm Air Coming Out of the AC
This could mean that your AC needs more refrigerant or that a return duct has detached and is now drawing in outdoor air. Either way, you're going to want a technician out there to address the issue.