An HVAC pump is a device that circulates air, water, or other fluids through a system. It works by using a motor to drive a pump impeller, which creates a vacuum that draws in the fluid. The impeller then pushes the fluid through the system, creating pressure and flow. The pressure created by the pump is used to move the fluid through the system, while the flow is used to regulate the temperature of the system. The pump is also responsible for maintaining the pressure and flow of the system, ensuring that the system is operating efficiently.