393 Copyright Goodheart-Willcox Co., Inc. 6 Chapter Review Summary • Voltmeters, ohmmeters, and ammeters are used to measure voltage, resistance, and current in a circuit, respectively. Voltmeters and ohmmeters should be connected in parallel with a load or circuit being measured. In-line ammeters must be connected in series with a circuit, while clamp-on ammeters measure by hooking their jaws around a single conductor in the circuit. • A multimeter is a single instrument that can measure multiple electrical variables, including voltage, current, and resistance. Many multimeters can also check diode operation, circuit continuity, capacitance, and temperature. • A power factor meter provides a direct reading of the power factor in an electrical circuit. A wattmeter is used to measure the wattage consumed by an electrical load. Like an ammeter, a wattmeter is connected in series with the circuit or load being measured. • A megohmmeter is an electrical insulation tester used to detect current leaks and conductor insulation failures. In HVACR, megohmmeters are mainly used to test motor winding insulation. In a hermetic compressor, the resistance of the winding insulation indicates the level of moisture and contaminants in the compressor. • Electrical diagrams are types of illustrations that show each component in a system and also show how it is wired to the next component in that system. Manufacturers often adhere electrical diagrams to the inside of equipment access panels. • Ladder diagrams show parallel paths for electricity to travel through a circuit. • Pictorial diagrams show pictures of components in place in relationship to how the unit is built. • Electrical problems are often the cause of service calls, so troubleshooting should begin with electrical tests. • Voltage testing helps ensure readings to the circuit, as well as across switching and load devices, is as expected. • Components should be tested when a potential electrical problem has been identified. • When an electrical problem has been identified, be sure to consider the root cause to avoid repeating the electrical problem. • A technician’s troubleshooting process may vary depending on the circumstances of the problem. However, it is important to keep an open mind to all potential causes of the problem rather than making assumptions based on one potential cause. • A technician’s approach to voltage testing may vary. There are several systematic methods that may be used, including hopscotching, from load outward, from control inward, and divide and conquer. • The convergence method of troubleshooting uses an IS-IS NOT chart as a tool to narrow down the cause of a problem. Review Questions Answer the following questions using the information in this chapter. 1. To measure voltage polarity correctly in a dc circuit, a technician should place the voltmeter’s red lead on the side of the load closest to the _____ side of the power supply. A. series B. parallel C. negative D. positive 2. Which of the following electrical instruments can be used to check for short circuits, open circuits, and shorts to ground? A. Power factor meter B. Wattmeter C. Ammeter D. Ohmmeter 3. Which of the following electrical instruments can only take an accurate reading when a circuit’s power is turned off? A. Power factor meter B. Wattmeter C. Ammeter D. Ohmmeter 4. Which of the following electrical instruments must be connected in series to take an accurate reading? A. Clamp-on ammeter B. Ohmmeter C. In-line ammeter D. Voltmeter 5. Which of the following electrical instruments wraps around the conductor it is measuring? A. Clamp-on ammeter B. Ohmmeter C. In-line ammeter D. Voltmeter