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Only a century ago, ice was hard to come by in most parts of the world. In hotter climates you had to buy your ice from a delivery service, which imported hefty blocks from a colder climate or from an industrial refrigeration plant. The price of ice was relatively steep, but if you wanted to keep your food cold, you didn't have much choice. In the hottest parts of the world, ice was a rare luxury. In an equatorial country, you might live your whole life and never even see a piece of ice.

This all changed in the early 20th century. Compact, affordable refrigerators brought the means of food preservation and ice production into the home and corner store. In the 1960s, new automatic icemaker machines made life even easier. These days, most Americans take ice completely for granted, even during the hottest days of summer.

In this article, we'll find out what's inside a typical home icemaker, as well as the larger commercial icemakers you might find at a hotel or grocery store. As we'll see, the basic process of making ice is very simple -- you just freeze water -- but spitting out perfectly shaped ice cubes is a fairly elaborate process.

The home icemaker's predecessor was the plastic ice tray. It's fairly obvious how this device works: You pour water into a mold, leave it in the freezer until it turns to a solid and then extract the ice cubes. An icemaker does exactly the same thing, but the process of pouring water and extracting cubes is fully automated. A home icemaker is an ice-cube assembly line.

Most icemakers use an electric motor, an electrically operated water valve and an electrical heating unit. To provide power to all these elements, you have to hook the icemaker up to the electrical circuit powering your refrigerator. You also have to hook the icemaker up to the plumbing line in your house, to provide fresh water for the ice cubes. The power line and the water-intake tube both run through a hole in the back of the freezer.

When everything is hooked up, the icemaker begins its cycle. The cycle is usually controlled by a simple electrical circuit and a series of switches. In the diagram below, you can see how the icemaker moves through its cycle.

At the beginning of the cycle, a timed switch in the circuit briefly sends current to a solenoid water valve. In most designs, the water valve is actually positioned behind the refrigerator, but it is connected to the central circuit via electrical wires. When the circuit sends current down these wires, the charge moves a solenoid, which opens the valve.

The valve is only open for about seven seconds; it lets in just enough water to fill the ice mold. The ice mold is a plastic well, with several connected cavities. Typically, these cavities have a curved, half-circle shape. Each of the cavity walls has a small notch in it so each ice cube will be attached to the cube next to it.

Once the mold is filled, the machine waits for the water in the mold to freeze. The cooling unit in the refrigerator does the actual work of freezing the water, not the icemaker itself (see How Refrigerators Work for details). The icemaker has a built-in thermostat, which monitors the temperature level of the water in the molds. When the temperature dips to a particular level -- say, 9 degrees Fahrenheit (-13 degrees Celsius) -- the thermostat closes a switch in the electrical circuit (see How Home Thermostats Work for details on this operation).

Closing this switch lets electrical current flow through a heating coil underneath the icemaker. As the coil heats up, it warms the bottom of the ice mold, loosening the ice cubes from the mold surface.

The electrical circuit then activates the icemaker's motor. The motor spins a gear, which rotates another gear attached to a long plastic shaft. The shaft has a series of ejector blades extending out from it. As the blades revolve, they scoop the ice cubes up and out of the mold, pushing them to the front of the icemaker. Since the cubes are connected to one another, they move as a single unit.
At the front of the icemaker, there are plastic notches in the housing that match up with the ejector blades. The blades pass through these notches, and the cubes are pushed out to a collection bin underneath the icemaker.

The revolving shaft has a notched plastic cam at its base. Just before the cubes are pushed out of the icemaker, the cam catches hold of the shut-off arm, lifting it up. After the cubes are ejected, the arm falls down again. When the arm reaches its lowest resting position, it throws a switch in the circuit, which activates the water valve to begin another cycle. If the arm can't reach its lowest position, because there are stacked-up ice cubes in the way, the cycle is interrupted. This keeps the icemaker from filling your entire freezer with ice; it will only make more cubes when there is room in the collection bin.
This system is effective for making ice at home, but it doesn't produce enough ice for commercial purposes, such as restaurants and self-service hotel ice machines. In the next section, we'll look at a larger, more powerful icemaker design.