"The indications that calls in an HVAC repair are the following: In case the HVAC unit do not produce enough cooling or heating. One should not confuse reduced heating or cooling with complete lack of heating and calling. The unit has been designed to produce certain amount of heating and cooling and if it does not produce that, it is good to get in touch with a service personnel. Most of the homeowners are aware of the electricity bill during each season of the year. Thus, suddenly if the utility bills increase, it might be so that your HVAC unit needs repair. This is because when there is stress on the system it uses more energy to produce similar amount of heating or cooling thus increasing the electricity bills. Certain sounds are common when your HVAC unit is operational but in case you get to hear unexpected strange noises like banging, clanging, buzzing or any other sound that is different from the ordinary, it is wise to call in a service expert because that may be a precursor to a forthcoming danger. "