"The common problems experienced by HVAC units are the following: • Blown Fuse • Worn out Contactor • Malfunctioning Capacitator • Dirty Filters • Wrongly set Thermostat or Thermostats which are not turned on • Refrigerant leak • Dirty Evaporator and Condenser Coil The DIY methods to troubleshoot an HVAC unit are the following: When the unit refuses to turn on, you can check the thermostat and ensure that it is on and the setting is either in the “heating” or the “cooling” mode as per the requirement. During the summer season, you can lower the temperature of the thermostat by 5 or 10 degrees while during the winter season, the temperature setting in the thermostat can be increased by 5 or 10 degrees similarly. At the same time, you can check for dirty filters, dirty condensers and accumulated debris near the outside unit. Filters of an HVAC system can be easily cleaned and it should be cleaned from time to time to ensure that the unit functions at the best of its efficiency. However, last but not the least, HVAC repairs most of the times is a costly affair so if you want to prevent that untimely expense it is a better idea to conduct annual maintenance of your HVAC system. It is recommended to get in touch with a reputed HVAC contractor who has the requisite expertise and knowledge to handle even the most complex HVAC systems. "