What are some common signs that my hvac system is not working properly?

When you feel warm air coming out of the vents in your house, check the thermostat. Head to your unit to investigate thoroughly but carefully. If your unit is outdoors, you should be able to hear and see if the fan is on. If you can see or hear the movement of the fan in your unit and feel air on the top, the fan is working and you can rule out that it is the problem with the unit.