In a chilled water plant startup, when should the chiller compressors be started relative to head pressure?

• A. Before head pressure is achieved.
• B. After head pressure is achieved.
• C. Simultaneously with pump start.
• D. Only after the tower is on.

Answer: (B)

Starting the compressors only after the head pressure (high-side pressure) has reached its design level ensures the condenser can effectively reject heat. If the compressor runs with insufficient head pressure, the refrigerant cannot condense properly, leading to excessive discharge pressure, motor overload, and potential equipment trips or damage. Establishing head pressure signals that the condenser water flow (tower and condenser circuit) is ready and that the system can circulate refrigerant safely. Once the head pressure is up to the setpoint, the compressor can operate under the proper conditions, allowing the evaporator to absorb heat and the chilled-water loop to run normally.