Chapter 25 Installation and Troubleshooting of Domestic Refrigerators and Freezers 651 Copyright Goodheart-Willcox Co., Inc. 8 component is not cut, damaged, or disconnected. The refrigerator-freezer can then be checked to see if it operates properly. Pro Tip Inspecting Electrical Connections Electrical connections must be clean and tight. If loose or dirty, they cause an unintentional resistance that often leads to overheating. Excessive temperatures can discolor the connection. The connection may be darkened by oxidation. A blue or greenish tint indicates overheating and corrosion. If the surrounding insulation is charred, overheating has occurred. The thermostat should be connected into the hot (ungrounded) wire of the circuit. This wire brings power to the motor from the electrical outlet. The wire returning power to the outlet is called the com- mon wire. The common is the grounded wire, not the green ground wire. To identify these wires within a refrigerator-freezer, follow the incoming wiring from the electrical plug in the wall outlet. Confirm these wires by consulting a wiring diagram for the refrigerator-freezer being serviced. Code Alert Switches on the Hot Wire The National Electrical Code states that switches cannot be installed in the grounded conductor. This implies that a power switch must break electrical power before it gets to an electrical load, not after the load in the common (grounded) wire. In other words, a switch should be wired in series with the hot (ungrounded) wire going to a motor, not after it. In the case of a refrigerator, the switch is the thermostat in series with the hot wire going to the compressor motor. Safety Note Preventing Shock It is important to have the thermostat in series between the hot wire and the compressor motor for safety reasons. This wiring prevents the motor from unintentionally turning on due to an internal short or fault and also to prevent the compressor from becom- ing electrically hot. An electrically hot compressor can cause an electrical shock to anyone who accidentally touches the compressor and completes the circuit. A system of green grounding wires connect to the equipment grounding conductor. This grounds all electrical components in a refrigerator or freezer. This ground is not intended to be a current-carrying wire. It is for safety only. It is used to avoid an electric shock if a short circuit occurs in the electrical system. Inspectin g Electrical Connection s Electrical connections must be clean and tight. If loose or dirty, they cause an unintentional resistance that often leads to overheating. Excessive temperatures c an discolor the connection. The connection may be darkened by oxidation. A blue or greenish tint indicates overheating and corrosion. If the surrounding insulation is charred, overheating has occurred . Switches on the Hot Wire The National Electrical Code states that switches c annot be installed i n t h e grounded conductor. Thi s implies that a p ower switch must break electrical p ower before it gets to an electrical load, not af ter the load in the common ( grounded ) wire. In other words, a switch should be wired in series with the hot ( ungrounded ) wire going to a motor, not af ter it. In the case o f a refrigerator, t h e switch i s t h e th ermostat i n series with t h e h ot wire going to t h e compressor motor . Preventin g Shock It i s important to h ave t h e th ermostat i n series b etween the hot wire and the compressor motor for safety reasons. This wirin g prevents the motor from unintentionally turning on d ue to an i nterna l short or fault and also to p revent the compressor from becom- in g electrically hot. An electrically hot compressor can c ause an electrical shock to anyone who accidentally touches the compressor and completes the circuit . Troubles such as open circuits and shorts to ground are easily checked with a multimeter. A test cord can be used to check four-pole motors. However, two-pole motors should be tested only by using a prop- erly sized relay in the circuit. These motors overheat if the starting circuit is connected for more than two or three seconds. When checking and servicing electrical circuits, first check the outlet electrical supply. Compare this with the appliance’s voltage specifications. Using a voltmeter, test the open-circuit voltage. Next, plug in the appliance and check the voltage again while it is running. The open-circuit voltage is likely to be slightly higher than with the motor running. However, this difference should not be more than 5 V. A small voltage drop between 5–10 V may be due to a clogged condenser, fan blade imbalance, or an electri- cal component that is drawing too many amps. If the unit has a voltage drop greater than 10 V, it is usually a sign that the compressor windings are shorted, a fan motor is locked up, or an electrical component has shorted out. Most refrigerators and freezers have a wiring diagram attached to the back. Locate the appropriate wiring diagram and check each circuit independently. Figure 25-10 shows the various electrical circuits typi- cally found in a domestic refrigerator. If a compressor fails to start, follow these steps: 1. Find out if electricity is reaching the compressor. 2. If it is, check the starting relay and circuit protectors. See Chapter 17, Servicing Electric Motors and Controls. 3. Disconnect all wiring from the compressor. 4. Check the compressor with a manual start test cord. Figure 25-11 shows a test cord for a typical compressor with Start, Run, and Common terminals. It uses two NO switches for the Run and Start functions. The ground clip, labeled 4, must be fastened to the compressor dome. The fuse is located in the black wire of the manual start test cord. Safety Note Connector Insulation All clips or connectors should be plastic-coated or should have a rubber boot over them to protect the tech--h nician from shocks, Figure 25-12.2 The diagram in Figure 25-11 shows that the start switch is controlled by the run switch. This means that the run switch has to be closed for the start switch to be able to function. Typically, the start switch is closed first, and then the run switch is closed. This allows both start and run windings to be energized simultaneously. Connector Insulation All c lip s or connectors should be plastic-coated or should have a rubber boot over them to p rotect the tec nician from shocks , Figure 25-1 .