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Repairing Heating Elements and Timers
Many appliances perform several functions — for example, the various cycles of a washer or dishwasher. These appliances operate automatically; once the on/off switch is turned on, switch components inside the appliance take over to control heat, water or fuel flow, motor speed, and other variables. The most important of these devices — used to operate switches, levers, and valves automatically — are solenoids (a current-carrying coil), relays, and sensor/responder pairs.
Heating elements work very simply. Unlike conductors, they are made of metal with high electrical resistance. When current flows through the element, this high resistance prevents it from flowing easily. Current must work to get through the element, and this work is converted into heat. When the current is turned off, the element cools. There are three types of heating elements: wire, ribbon, and rigid. To determine whether a heating element is functioning:
Step 1: Disassemble the appliance to access the element and test it with a continuity tester or a VOM set to the RX1 scale.
Step 2: With the appliance unplugged, hook the clip of the continuity tester to one terminal of the heating element and touch the probe to the other terminal; or touch one probe of the VOM to each terminal. If the element is functioning, the tester will light or buzz; or the VOM will read from 15 to 30 ohms. If the tester doesn’t light or buzz, or the VOM reads higher than 30 ohms, the element is faulty. Replace it.
Note: If you use a continuity tester, look closely at the tester, especially if it is the light-up type. Some heating elements have an extremely high resistance factor, and the light may produce only a dim glow or a faint buzz. This reaction does not mean that the element is faulty, but rather that it converts current to heat efficiently.
The operation of a major appliance that has several cycles (for example, a washer, dishwasher, dryer, frost-free refrigerator, or range) is controlled by a timer — a complex rotary switch powered by a small synchronous motor. The timer consists of a shaft, gears, and a series of notched cams, one for each circuit or cycle.
The timer itself is powered by the timer motor; the appliance is powered by the much larger appliance motor. When the switch is turned on, electrical contact is made with the timer motor, and a spring on a trip arm is coiled. The arm trips when the spring is tight, releasing the spring and moving the cam of the switch to the next circuit. At the last cycle, contact with the motor is broken, and the timer turns the appliance off.
When a timer malfunctions, it should usually be replaced. Professional rebuilding is sometimes possible, but this is likely to be more expensive than replacement. Many timers are sealed units. Some timers have an adjustment shaft, which can be turned with a screwdriver blade. To determine whether a timer is functioning:
Step 1: Test the timer with a continuity tester or a VOM set to the RX1 scale. Make a sketch of the timer wires and then, with the appliance unplugged, disconnect all timer wires from their terminals. Make sure you’ll be able to reconnect the wires exactly the same way.
Step 2: Touch or clip one probe of the tester or the VOM to the common terminal. Touch the other probe to each cycle terminal in turn. Rotate the timer control knob as you work. The continuity tester should light or buzz at each circuit; the VOM should read zero.
Step 3: If one or more circuits do not give these results, the timer is faulty and should be replaced. To replace a timer, disconnect its wires one at a time, connecting the corresponding wires of the new timer as you progress in order to avoid the chance of a misconnection.
Digital timers typically cannot be repaired and must be replaced.
Repairing a heating element didn’t seem that dangerous, right? Well, heating elements lack a key ingredient that makes the repairs in our next section so dangerous — combustible gas. Move on to the next page to learn how to repair a pilot light or thermocouple.