All HVAC systems must be protected by a

• A. Check valve
• B. Pressure relief valve
• C. Auto stop switch
• D. Overflow drain

Answer: (B)

The protective device being described is a pressure relief valve. When system pressure climbs beyond a safe limit, this valve automatically vents excess pressure to prevent damage to vessels, pipes, and components, reducing the risk of ruptures, leaks, or other hazardous failures. A check valve only prevents backflow, not overpressure. An auto stop switch may shut the system down under certain faults but doesn’t vent or relieve pressure. An overflow drain handles condensate or water buildup, not the pressure in the refrigerant or air system. So, the pressure relief valve is the device that provides automatic overpressure protection for HVAC systems.