Residential Air Conditioning Systems Mechanic (313D) Certification Practice Exam

The "C" terminal, which stands for the common terminal in control systems, is typically supplied with 24VAC (volts alternating current). This low voltage is standard for many residential air conditioning and heating systems, allowing for safe operation of control components such as thermostats and relays without the risks associated with higher voltages.

Using 24VAC provides a reliable power source while minimizing injury risk during installation or servicing. This voltage is also conducive to the functionality of various control devices, maintaining efficiency in the system's overall operation. Understanding the significance of this supply voltage is crucial for anyone working with residential HVAC systems. Higher voltages like 120VAC or 240VAC are typically reserved for power supply to the larger components of the HVAC systems themselves, while the 48VAC supply is not a standard voltage used in these applications. Thus, the specific application of 24VAC reinforces its status as the default for the "C" terminal in HVAC control systems.