Didn’t know you could make ice by vacuuming water.
You have to bring it below the "triple point" in order to freeze water. When water boils, its temperature stays exactly at its current boiling point.
In the chart below it shows a line at 1 atmospheric pressure (atm) and a line at 100 celsius, and where they intersect is the normal boiling point of water. Any water above 100C immediately becomes steam and bubbles away from the rest of the liquid.
As pressure goes down, so does the boiling point, and when it gets below the triple point at 0.06 atm, the boiling point & freezing point collide... so the water that boils away should take away heat until the remaining water is cold enough to freeze. (It's best to do this in the dark, because light can still transmit heat even through a vacuum. That's why sunlight is warm even through the void of space. If you keep shining light on the water at low pressure, you'll end up with very little ice, or none at all.)
Fun additional info... Dry Ice (Frozen CO
2) is below its triple point at 1 atm. That's why it sublimates (at -78C) instead of melting. In order to melt it into a liquid, you would have to raise the pressure above 5.2atm (about 76.5 PSI).