When you do not maintain your HVAC system, a variety of things can happen. For one thing, if your HVAC system isn't properly maintained, its efficiency will suffer. What you may not realize is that your HVAC and its components require a regular check-up, cleaning, or lubrication to function properly. If you don't, the system will be put under undue strain, causing your energy consumption to spiral out of control. It will appear on your utility bill later.