•• Permanent split capacitor (PSC). •• Capacitor-start, induction-run (CSIR). • Capacitor-start, capacitor-run (CSCR). 25.3.1 Shaded-Pole Motor The shaded-pole motor is a uniquely designed, low-cost motor used to operate small fans, such as the evaporator and condenser fans on domestic and light commercial refrigeration units. See Figure 25‑16. The shaded pole motor has very low starting torque, but it can carry a full load once it is up to speed. The capability of carrying a full load makes the shaded-pole motor ideal for oper- ating small fans. At start-up, the only load on the motor is the weight of the fan blades. Full load is not reached until the blades are turning at oper- ating speed and moving volumes of air. Construction of the shaded-pole motor is different from construction of other induction motors. As shown in Figure 25‑17, a slit is cut at the edge of each stator pole, producing a small prong. A copper band, called a shading coil, is placed over the prong. The shaded pole produces a tiny magnetic field out of step with the main poles. It is not a start winding in the usual sense because the shading coil is not connected to a power source. The shaded pole provides just enough magne- tism to start the rotor turning. Then the rotating magnetic field in the main poles provides the necessary torque to bring the rotor up to full speed. the current draw of the motor and the tempera- ture of the windings much better than can external overloads. Internal overload protection is installed at the factory and is not accessible to the techni- cian. See Figure 25‑15. The internal overload is a bimetallic element that will open the circuit and stop the motor if the winding temperature reaches 200°F to 250°F (93°C to 121°C). It will close again when the winding temperature drops to 150°F to 175°F (66°C to 79°C). Depending on ambient temperature condi- tions, it may take one or two hours before the protector cools enough to close the contacts. Cooling the unit with forced air or ice speeds up the process. Unless an ohmmeter test confirms an open motor winding, do not condemn a motor until sufficient time has passed for the overload to reset. 25.3 Types of Induction Motors In HVACR applications, five types of single- phase induction motors and also the three-phase induction motor are in general use. The type of motor for a particular application is determined by the location and type of load. Each motor is available in various horsepower ratings. Single- phase induction motors are described in the order of turning power (torque), from the least to the greatest. The three-phase motor is described later in this chapter. The types of single-phase induction motors are: • •• Shaded-pole. • Split-phase. C R S Motor winding Goodheart-Willcox Publisher Figure 25‑15. An internal overload built into the motor windings is not accessible to the technician. Goodheart-Willcox Publisher Figure 25‑16. A shaded-pole motor used to operate a condenser fan on a light commercial refrigeration unit. 494 Heating and Cooling Essentials Copyright Goodheart-Willcox Co., Inc.