Don’t you just enjoy the sound of that A/C of yours on a hot day? A quick hum starting out, and you can rest assured that you will be cooler with that air conditioning system coming out of the A/C vents any moment. Then the constant hum of the outside HVAC component as it continues producing that chilly air. However, what would happen if that proper hum no longer sounded? If your air conditioning system stopped working, and that hum is gone? I would first check the climate control component to ensure no child of mine played with it while I was out. I would verify that the “cooling mode” was respectfully indicated on the control unit. If all is well at the control unit, I would then transfer onto the electrical box. If there had been a power surge while I was absent from my home, the breakers might need to be flipped off and back on again. I would not forget to check the air filter at this pressing time, just in case of a noticeable clog in the HVAC system. If still, that proper air conditioning system hum is not heard, I would double-check the outside HVAC component to ensure that no tree limb had fallen on my unit. If it is all clear on the outside A/C equipment, I would have to call for an immediate HVAC appointment. In this heat, I cannot sit, sweat and become miserable in my own home. Then I would have to go out to the motion pictures to get some much-needed A/C until my air conditioning system repair supplier arrives.