375 6 ▲ Danfoss Introduction HVACR technicians must know how to test electrical circuits in order to properly troubleshoot and service HVACR systems. Following good safety practices and being able to read electrical diagrams are the first steps to mastering a skill that requires practice and experience. An HVACR technician can achieve a high degree of success by following an established procedure and performing electrical troubleshooting one step at a time. Safety is the most important aspect of working on electrical equipment. Before any service is performed, de-energize and lock out the circuit being serviced. 17.1 Electrical Test Equipment The most commonly used instruments for testing electrical circuits are the volt- meter, ohmmeter, and ammeter. These three instruments are most often available in one multi-instrument called a multimeter. Two other electrical meters occasion- ally used are the power factor meter and wattmeter. In HVACR, most electrical sys- tem and motor troubleshooting can be done with just one of these instruments: the multimeter, which can measure voltage, current, resistance, and other variables, depending on the model. In addition to these instruments, a service technician’s toolkit should include insulated gloves rated for high-voltage use and protective eyewear. Tool sets should also include screwdrivers and pliers that are properly insulated. Some multimeters use a Bluetooth transmitter to transmit the reading to a technician’s phone. This enables the technician to hook up the meter, start the unit, and read and record the meter readings from a distance away from the unit. 17.1.1 Voltmeters The instrument used to measure voltage in electrical circuits is called a voltmeter. A voltmeter measures the potential difference between two points in a circuit. If there is no potential difference between two points, there will be no voltage reading. For instance, if a voltmeter is used to measure the voltage across a length of conduc- tor that has no electrical load or virtually no resistance between the points being measured, the voltage reading will be nearly 0 V. Voltmeters are either analog or digital. Analog voltmeters use magnetism to move a needle across a scale and show the voltage supplied to an electrical device. Digital voltmeters use solid-state circuitry to measure voltage. Having no moving parts, digital voltmeters display their readings on a small screen. In general, digital meters are more accurate and remain calibrated longer than analog meters. Voltmeters have two leads: one red and one black. Each voltmeter lead is placed on either side of an electrical load, and then power is applied to the circuit to mea- sure the voltage across that load. A voltmeter is connected in parallel with the load or circuit it is measuring, Figure 17-1. ammeter clamp-on ammeter continuity in-line ammeter ladder diagram megohmmeter multimeter pictorial diagram power factor meter voltmeter Technical Terms