In starting up a chilled water system, the first piece of equipment to start should be the:

• A. compressor if it has a built-in oil pump
• B. chilled water pump
• C. compressor oil pump
• D. condenser water pump

Answer: (B)

When starting a chilled water system, establishing proper flow on the water side is the priority. The chilled water pump must come on first because it circulates water through the evaporator and through the building coils to absorb heat. If the refrigerant is driven by the compressor without adequate water flow, the evaporator can overheat, the refrigerant may not absorb heat effectively, and the compressor can suffer from high discharge temperatures, potential lubrication problems, or damage from lack of heat transfer.

Starting the chilled water pump first ensures there is immediate, continuous cooling in the evaporator once the compressor starts. The other pieces—oil pumping for the compressor, the condenser water pump, and the compressor itself—are important, but without water flow, initiating the refrigeration cycle is unsafe and inefficient. Once water flow is established, you can bring the compressor online and then start the condenser water pump to reject heat.