If you are like most people, you do not change your air filter often enough, this allows dirt to get into the unit.
Having a qualified air conditioning tech come out to your house and check out the unit before it gets too hot has several benefits; It helps the unit perform better, last longer, it can help locate issues before they become costly problems and perhaps one of the best benefits is you can have the work done while the tech has the time to do the job right. Don’t wait till it is too late.
One trick Arizona home inspectors use it to check the air temperature at the filter and at a register while the air conditioner is running and look at the difference in temperature. Phoenix home Inspectors look for temps between 17-22 degrees if it is real humid (monsoon season) it may be as low as 15°F. (Note just because the temperature split is good does not mean the unit is fine, If the unit is low on refrigerant the split may be low, if the coil is dirty the split may be high, if the coil is dirty and the refrigerant is low the split may be fine but the unit will be working overtime to cool the place.
The bottom line is only a person qualified person is going to be able to verify your unit is functioning properly but proper maintenance and having the unit professionally serviced every year or two will go a long way towards keeping your home comfortable.