650 Modern Refrigeration and Air Conditioning Copyright Goodheart-Willcox Co., Inc. Tubing that rattles against refrigerator parts should be carefully bent so it no longer contacts those parts. Be very careful not to kink the tubing as you bend it. The tubing may be rigid, but may have a vibration or hum (harmonic vibration). This noise can be reduced by clamping rubber blocks on the tubing, Figure 25-9. Loose baffles and ducts can be secured with self- tapping sheet metal screws or sealant. Care should be taken when working on an evaporator to prevent puncturing the tubing. 25.2.7 Unusual Cycling Times Cycling time on home refrigerators and freez- ers cannot be given in definite terms. Cycle times vary depending on several factors. These include the amount of storage space inside the cabinet that is being used, the temperature outside the cabinet, and the compressor condition. Placing warm food in a cabinet to be frozen will also affect the cycling time. In many systems, the compressor runs roughly one-third of the time. In other words, it may run five minutes and be off ten minutes. It may run for ten minutes and be off for twenty minutes. This ratio of on and off time is referred to as the refrigerator’s duty cycle. Any unusual or unexpected changes in cycling time should be investigated immediately. They may indicate that trouble is developing in the system. 25.2.8 System Failure The failure may be that the unit is running as nor- mal, but is not maintaining the proper temperature or the compressor motor is not running or is running erratically. The following sections provide some sug- gestions for troubleshooting the system based on each of those conditions: Compressor Runs, but Cabinet Temperature Is Incorrect • Check for cabinet leaks. • Check for evaporator icing. • Check for good air circulation over the condenser. • Check for dirt or dust buildup on the condenser. • Check the temperature control systems and components. • Check the internal operation of the system. Compressor Does Not Run or Runs Erratically • Problems may be in the external circuits of the refrigerator. Eliminate external electrical components as a possible cause first. • Check the motor. 25.3 Checking External Circuits It is important to locate trouble and determine its cause accurately. Sometimes expensive compressors are needlessly replaced because they are believed to be faulty. The real trouble, however, may be in less expen- sive and easily repaired external devices. Always eliminate external components and wiring as a source of problems before diagnosing and replacing internal components. Problems in refrigerator-freezers are frequently caused by failures in the wiring or auxiliary systems. Common sources of problems include the following: • Power-in connections. • Thermostat. • Wire terminals. • Relays. • Capacitor (if the unit has one). • Defrost timer. Each of these devices should be checked carefully before the compressor or core refrigeration system components are suspected. These parts can be checked best by removing them from the wiring system. After they are isolated from the rest of the system, the parts can be checked independently. As an alternative, each part can be temporarily replaced by a test part of the proper size or capacity and known to be in good work- ing order. Also make sure the wiring going to each A B Goodheart-Willcox Publisher Figure 25-9. Two ways to reduce noise caused by vibrating tubing. A—Wrap tape around the tubing where the tubing touches the cabinet. B—Put tape or a rubber block on the tubing in the center of a vibrating section.