Residential HVAC Installation Practice Exam

The distinction between a mechanical thermostat and a digital thermostat primarily revolves around the technology and mechanisms each employs for temperature control. A mechanical thermostat operates using a physical mechanism, commonly a mercury switch, which reacts to temperature changes. The mercury inside the switch moves in response to temperature variations, opening or closing contacts to turn the heating or cooling system on or off. This design is straightforward and has been used for decades in residential HVAC systems.

In contrast, a digital thermostat relies on electronic sensors and a microprocessor to monitor and control the temperature. This allows for more precise temperature readings and can enable features such as programmable settings that adjust the temperature according to a schedule or user preferences.

The presence of the mercury switch in mechanical thermostats is a key factor that differentiates them from digital models, making this the correct statement. Understanding this difference helps in recognizing the operational principles of these devices and their respective advantages in various residential HVAC settings.