Air controls are located on the top edge of the spa shell (most hot tubs). Once rotated and turned on they allow water flowing through the jets to suck air into the venturi, adding extra "fizz" and "bubbles". If water is coming OUT of the air control, you will have a jet blockage. Try removing the jets and clean out dirt and debris. Make sure the jets are clean and any O rings, seals and gaskets are in good condition.