Question 65 3AE02 - Third Assistant Engineer (Alt)

The Correct Answer is A **Explanation for A (Correct Option):** In a self-contained recovery unit flow diagram (like Illustration RA-0032), FS2 typically stands for a **Float Switch** or a similar liquid-level sensor placed strategically near the evaporator or surge drum within the recovery unit's internal refrigeration circuit. When recovering large amounts of liquid refrigerant from the appliance (direct liquid recovery mode), this liquid flashes/evaporates inside the unit. If the rate of incoming liquid refrigerant exceeds the unit's ability to evaporate it quickly, the liquid level rises and activates FS2. The activation of FS2 signals the control system to switch operational modes—specifically, to stop trying to recover bulk liquid and instead switch the flow path to continue recovering the remaining refrigerant as vapor (direct vapor recovery mode). This prevents liquid slugging back to the compressor and ensures the maximum possible recovery before the unit reaches the required vacuum level. Thus, its function is the automatic transition from liquid recovery to vapor recovery. **Explanation of Incorrect Options:** * **B) It automatically shuts down the recovery unit compressor when the discharge pressure becomes excessive.** This function is performed by a high-pressure cutout switch (typically labeled HP or HPC), which is a pressure-activated safety device, not a liquid-level/float switch (FS). * **C) It automatically shuts down the recovery unit compressor when the refrigeration system has reached a depth of 15" Hg.** This function is handled by a low-pressure switch (typically labeled LP or LPC) or the primary control logic measuring system pressure. While the unit might shut down upon reaching a required vacuum level, this is a pressure control function, not the function of a float switch (FS2). * **D) It automatically shuts down the recovery unit compressor when the recovery cylinder becomes 80% full.** This safety function is performed by a dedicated 80% overfill sensor (typically a weight scale or a float switch/sensor mounted directly on the external recovery cylinder itself, sometimes labeled FSO or using a transducer), which is separate from the internal operational control switches like FS2.