How often an HVAC should be checked depends on the type: gas, electric, oil, heat pump.
Electric resistance systems require the least amount of servicing because there are less parts that can go bad. It should be cleaned once every 5 years.
Gas systems require service every one or two years.
Heat Pump systems require service every one or two years depending on how much run time they receive.
Oil systems by far require the most amount of maintenance. Maintenance should include cleaning and minor part replacement. Maintenance should be performed every year.