Copyright Goodheart-Willcox Co., Inc. Chapter 17 Electrical Troubleshooting Fundamentals 389 6 circuit. Depending on the fault, parts of a circuit may remain energized even after the circuit is disconnected at the disconnect box. • Remove the device from the circuit before testing. If you test the device while it is still connected to the circuit wiring, your testing measurements may be affected. • Prior to disconnecting a device, use your phone to take a photo of the connections at its terminals. You can also label the wires with tape or write the connections on a piece of paper. This will help ensure you reinstall or replace the device correctly. • Always test the device that appears to be faulty—do not assume that the device is bad only because a voltage check was incorrect. In some cases, the faulty voltage measurement could have a different cause. 17.3.3 Investigate Root Cause of Fault In some instances, the apparent fault or problem may be the result of a different problem—the root cause. Once you have identified the initial problem, consider what could have caused the problem. For example, if the problem is a tripped circuit breaker, you need to investigate potential problems that could result in a tripped breaker. 17.4 Electrical Troubleshooting Strategies The basic steps of electrical testing presented in the previous section provide a general framework for trouble- shooting. In reality, a technician’s process for testing elec- trical system components is determined by several factors: • Information gained during the customer interview and observed during the initial inspection. • Equipment troubleshooting charts. • Knowledge and experience with the specific type of unit being serviced. These factors help a technician target likely causes and troubleshoot efficiently. However, becoming too focused on one specific cause and making assumptions about the problem can lead to missing the root cause. If the root cause of the problem is not addressed, a callback is likely to occur. Based on the initial information, a technician may choose to use several approaches for voltage testing: • Hopscotching. Hopscotching is used to determine the location of an open switching device or wire in a circuit. Using the ladder diagram for the circuit, the technician takes several voltage measurements. One probe remains placed on the load voltage (right rail of the ladder diagram), and the other probe is moved from left to right, beginning with the line voltage (left rail of the ladder diagram) and then moving through each switching device. When a 0 V measurement occurs, an open is identified. See Figure 17-21. • From load outward. In this method, voltage at the load device is checked first. If there is no voltage at the load device, the technician works tests devices in sequence moving “out” from the load device along the circuit path. Each switching device is checked until an open is found. 120 V OFF A COM V Ω A V Ω 0 V OFF A COM V Ω A V Ω Fan Motor Receiving Voltage, Problem Is in Motor Fan Motor Not Receiving Voltage, Problem Is in Circuit Goodheart-Willcox Publisher Figure 17-20. Ladder diagram for a fan motor circuit. The switch is closed but the fan motor is not energized. In the first example, the 120 V measurement at the fan motor indicates that the motor is receiving the proper voltage. Thus, the problem is likely in the motor. In the second example, the 0 V measurement across the motor indicates that the motor is not receiving the proper voltage. The problem in the circuit must be addressed before the motor can be accessed.