Blowing hot air
This is the most obviously and randomly found problem in residential air conditioners. Your air conditioner will blow air at room temperature. The problem could issue out of number of reasons such as - thermostat not working, clogs in your filter, piping/duct work, and many more. It is surely repairable. But sometime the reason could be serious enough and replacement of the unit would be wise. However the crux of the matter is that lack of air flow is a sure sign that you have a problem which must be dealt with.
Not dehumidifying
An air conditioner also dehumidifies the room air to maintain the correct level of humidity in the room. This is very important for the health of the inmate of the house. Too much humidity in the room can breed mold and mildew in the house which can cause series of health hazards. The most obvious reason for high humidity is refrigerant leak in the air conditioner. Call a HVAC technician to come and repair your A/c/ They will know whether the unit would be repaired or replacement is a better option.
Bizarre sounds
Sound from an air conditioner is a very common problem. However, no matter what kind of sound you hear, be it grinding, squeaking or chattering, never ignore it. Call a technician ASAP. Many people take sounds as sign of aging. But that is not necessarily the case. The reason could be a very minor one – such as loose components. But sometimes rattling sound coming out of A/c could be due to a failing compressor. Hire a heating and air conditioning professional to check it out. Changing the compressor is a costly repair. It would be better to buy a new unit than changing the compressor. A/c units are designed to operate at a noise level that is barely audible. Under such conditions, if your cooling system is drawing attention to itself, you know it’s time to upgrade to new equipment.