A correctly installed air conditioner should cool the room noticeably within a few minutes of being turned on, operate quietly without unusual vibrations or rattling sounds, and show no signs of refrigerant leaks such as ice buildup on the lines or an oily residue around the fittings. The indoor unit should be mounted level and securely on the wall, the drainage pipe should be releasing water properly to the outside without any leaking inside the room, and all electrical connections should be properly insulated and safely routed. If the unit struggles to reach the set temperature, makes abnormal noises, or if water drips from the indoor unit onto the wall or floor, contact the installing technician immediately to inspect the setup before using the unit further.