Common appliance switches include (left to right) rocker, toggle, slide, and contact (tamper) switch.

Actually, appliance controls aren't household things--they are parts of things. Because they are parts of dozens of things in your home, knowing how to fix them is vital to fixing many things you own. For example, nearly all small and large household devices--from table lamps to heating furnaces--include switches. A few appliances with thermostats include the heating pad, hair dryer, toaster oven, and crock pot. You'll find timers in the coffee maker, washer, dryer, dishwasher, and microwave, just to name a few. Knowing how appliance controls work and how to fix them earns accolades in the Fix-It Club.

How Do They Work?

Appliance controls are the devices that turn things on and off, regulate temperature, speed, duration, and otherwise control appliance functions. Appliance controls include switches, thermostats, rheostats, and timing mechanisms. Some appliances, such as toasters, use mechanical controls while others, like microwave ovens, use digital controls. Knowing how they work will help you fix just about any of them.

Variable-speed switch from a food mixer.

Appliance switches vary in complexity and functions. Switches operate by making contact with the conductor of an electrical circuit. When an appliance is plugged in, it's connected to an electrical circuit in your home. Power runs through the wires of the circuit to the appliance. When the appliance's on-off switch is turned on, electricity flows through the switch to operate the appliance. There are several common types of switches: push-button, toggle, rocker, slide, and throw switch.

Other appliance controls are also switches. Rheostats, thermostats, solenoids, and timers, for example, are all types of switches. These components operate inside appliances to turn on motors, open and close valves, control heating elements, and turn on different parts of the appliance during different cycles, such as the rinse and spin cycles of a washing machine. Let's take a closer look at them.

The round device on the right is a thermostat inside an electric heater.

A thermostat is a switch that controls temperature in a heating element or a cooling device. It opens and closes a circuit to furnish current based on temperature. Thermostats used in appliances may use a bimetal strip, bimetal thermodiscs, or a gas-filled bellows chamber to control the electrical contact. If faulty, they should be replaced rather than repaired.

A rheostat is a variable controller that directs the amount of current flowing to many older appliance components. A blender with a dial control that can be turned to increase or decrease motor speed uses a rheostat to do so. Because rheostats can be damaged by moisture, they can easily malfunction.

A timing mechanism controls current flow based on a mechanical or digital timing device similar to a clock. Timing mechanisms on small appliances usually turn the appliance on or off. Timers on major appliances--washing machine, dishwasher, dryer, frost-free refrigerator, or oven, for example--control the various cycles. Mechanical timers on large appliances consist of a shaft, gears, and a series of notched cams, one for each circuit or cycle. The timer is powered by a small timer motor. Digital timers are much simpler, using low-voltage electricity to control various functions such as turning on or off a device. While some timing mechanisms can be adjusted, those that are faulty should be replaced rather than repaired.

Many of these mechanical controls have been replaced, or at least are assisted, by digital controls. The good news is that digital controls are relatively trouble free, going many years without service. The bad news is that when they do go out, there's no repair to do; you simply buy another unit and plug it in exactly as the old one. Of course, make sure you've solved any other electrical problems first so the digital controller won't be damaged on installation.

What Can Go Wrong?

What can go wrong with appliance controls? They can quit controlling! Switches won't turn on and off, thermostats don't properly regulate heat, rheostats don't provide smooth control, and timers quit timing. In many cases, all that's needed is a good cleaning or reconnecting the wires. Otherwise, the controller should be replaced rather than repaired.

Fix-It Tip

Sometimes the only problem with a controller is that an electrical connection to or from it has become loose. With the appliance unplugged, carefully wiggle the connection to make sure that it fits snugly. If there is corrosion at the terminal, remove the connection and clean the terminal with a small brush.