In a multi-cylinder reciprocating compressor that uses cylinder unloaders to regulate capacity, what would occur if some unloaders fail to operate when needed?

• A. The discharge pressure would drop
• B. The chilled water temperature will increase
• C. The compressor would run at maximum speed
• D. System efficiency would double

Answer: (B)

Capacity control relies on unloaders to match the compressor’s capacity to the cooling demand. If some unloaders fail to operate when needed, the compressor can’t back off and ends up delivering near full capacity. In a chiller, excessive refrigerant flow into the evaporator can exceed what the chilled-water loop can absorb at the current flow rate, reducing heat transfer efficiency and causing the water leaving the evaporator to be warmer. That’s why the chilled-water temperature would rise. The other outcomes—lower discharge pressure, a motor speeding up, or a sudden doubling of system efficiency—don’t align with how unloading affects the cycle.