Copyright Goodheart-Willcox Co., Inc. 262 Essential Electrical Skills for HVACR: Theory and Labs An advantage of the PSC is its slower ramping start-up. This is helpful when sound must be minimized, such as when operating an evaporator blower quietly. The PSC also draws less start-up current than the CSIR and RSIR. Air handlers need more than one speed. Forced warm air requires less speed than air conditioning. The multi-speed PSC can produce up to four speeds. Connections along the run winding, called taps, make it possible to select more or less winding resistance. Less winding resistance results in more current flow and greater speed. See Figure 13-16. These multi-speed motors have six to eight poles. 13.3.4 Capacitor-Start, Capacitor-Run The capacitor-start, capacitor-run (CSCR) motor, also called a CSR, is the highest start- ing torque split-phase motor. When the motor is starting, both run and start capacitors are wired in parallel to each other and in series with the start winding. Capacitors in parallel increase the starting torque. The start capac- itor must be removed from the circuit when the motor reaches between 60% and 75% of its rated speed. See Figure 13-17. After the start capacitor is removed from the circuit, the CSR operates as a PSC motor. Thus, the CSR has the same efficiency benefit of the PSC. The CSR can be used with up to 5 tons of air conditioning and many refrigeration applications. This motor is also used in large air handlers. 13.3.5 Shaded-Pole Motor The shaded-pole motor is not a split-phase motor because it only has a run winding. In order to self-start, it uses a copper band that produces the secondary out-of-phase mag- netic pole to create the rotating magnetic field effect. See Figure 13-18. These motors have minimal starting and running torque. They are used for small fans and small condensate pumps. The rotor rotation cannot be changed unless it is a special service type motor that has provisions to alter the band or a rotor-to- frame configuration. Shaded-pole motors are available from less than 1/100 hp to around 1/6 hp. This is the least efficient motor at about 50%. 13.4 Split-Phase Motor Starting Devices A centrifugal switch cannot be used in explosive atmospheres or inside hermetic compressors. The arcing caused by switching current on and off can ignite gases. It can also create a short circuit if used in a refrigerant and oil environment inside a her- metic compressor. Four common devices are used to remove the start winding and starting capacitor. These are the current magnetic relay, PTC relay, potential relay, and electronic starting relay/timer. S R L2 C L1 CSCR Run Start Centrifugal switch Goodheart-Willcox Publisher Figure 13-17. CSR motor diagram using a centrifugal switch to remove the start capacitor from the circuit. Motor shaft Rotor Stator Shaded pole Motor windings Shaded pole Dial Manufacturing, Inc. Figure 13-18. Shaded-pole motor.