viii The instructional design of this textbook includes student-focused learning tools to help you succeed. This visual guide highlights these features. Chapter Opening Materials Each chapter opener contains a chapter outline, a list of learning objectives, and a list of technical terms. The Chapter Outline summarizes the topics that will be covered in the chapter. Objectives clearly identify the knowledge and skills to be learned when the chapter is completed. Technical Terms list the key words to be learned in the chapter. Additional Reading directs the student to more content coverage found in Modern Refrigeration and Air Conditioning. Introduction provides an overview of the chapter content. Additional Features Additional features are used throughout the body of each chapter to further learning and knowledge. Safety Notes alert you to potentially dangerous materials and practices. Pro Tips provide advice and guidance that is especially applicable for on-the-job situations. Illustrations Illustrations have been designed to clearly and simply communicate the specific topic. Illustrations have been completely replaced and updated for this edition. Pho- tographic images have been updated to show the latest equipment. Features of the Textbook Copyright Goodheart-Willcox Co., Inc. 281 algorithm bi-directional communication closed-loop system diagnostics direct digital control (DDC) event input integrated furnace controller (IFC) lookup table open-loop system output printed circuit board (PCB) programmable logic controller (PLC) signall trace varistor Technical Terms 14 Troubleshooting Printed Circuit Board Control Systems 14.1 Printed Circuit Board Structure 14.1.1 Microprocessor-based PCB (Controller) Operation 14.2 Troubleshooting the PCB 14.2.1 Microprocessor-based PCB (Controller) Applications 14.3 Heating System PCB 14.4 Air Conditioner System PCB 14.5 Communication After completing this chapter, you will be able to: • Discuss the function of a printed circuit board (PCB). • Define an input. • Define an output. • Explain an algorithm. • Discuss the purpose of a lookup table. • Define bi-directional communication. • Discuss system annunciation and diagnostics. • Describe the operation of a microprocessor-based PCB. • Explain how to troubleshoot a PCB. • Describe microprocessor-based PCB applications. • Discuss the process of a heating system PCB. • Discuss the process of an ac system PCB. • Explain microprocessor-based PCB communication. Chapter Outline Learning Objectives Additional Reading Modern Refrigeration and Air Conditioning, 21st edition 14.3 Circuit Boards and Microprocessors 18.3 Servicing Fan Motors 38.5 Blower Controls 45.5 Building Control Protocols Introduction Modern HVACR equipment uses microprocessor-based controls. The microprocessor and its supporting electronic are mounted on a printed circuit board (PCB). A PCB receives input signals from system sensors and switches. The microprocessor’s algo- rithm then uses this information to produce output signals to control an HVACR system. cosmopolit/Shutterstock.com , n ccomponents s rm Copyright Co., Inc. 108 Theory 3. Zero or close to zero is displayed. The coil is shorted. This means the wire insulation has melted away resulting in a short length of wire with insignificant resistance. This coil should not be powered up, as it will cause a direct short. See Figure 7-18. When troubleshooting a coil in a live circuit, the first step is to check for its correct applied voltage. If voltage is present and the coil is not energized, turn off power and check for faulty connections. If connections are good, then disconnect one end of the coil, and then check resistance. An OL reading confirms that the coil is open and must be replaced. A shorted coil trips a cir- cuit breaker. When checking the coil resistance, it could be 0 Ω but can also be OL. The intense heat produced by the short circuit can cause the wire to break. Before replacing the solenoid coil, a technician must investigate why the part failed—otherwise the new part may also fail. 7.3 Relays and Contactors A relay is an electrically operated switch controlled by an external signal. In most HVACR configurations, relays have a movable contact attached to an armature and a fixed contact attached to a stationary structure. These parts make up a set of contacts. Relays can have multiple sets of contacts configured as normally open or normally closed combinations, Figure 7-19. Normally open (NO) contacts are open Ohmmeter Tests for Coils Note that the above ohmmeter test is used for all coils used in solenoids, relays, contactors, transformers, and motor windings. All of these components are made from one or more coils of wire. Pro Tip Melted insulation — bare wires contacting Rules No 2. Isolate coil Load 1 2 0.0Ω VΩ com A Ω V V 0 Ω — Shorted Coil Goodheart-Willcox Publisher Figure 7-18. The display of 0 Ω on the multimeter indicates the coil shorted. Single-pole single-throw Single-pole single-throw Single-pole double-throw Single-pole double-throw Double-pole double-throw Double-polee single-throww Goodheart-Willcox Publisher Figure 7-19. Cop right GGoodheart-Willcox 1 8 EEssentiall sse tia EElectricall lec rica SSkillsls k l fforr HHVACR:: V CR Th ory aandd LLabssb DDouble-poleleope-blou doubdouble-throwrow-thel pol si DDouble-pole ouble-pole ssingle-throw ing re 7- 9. CContactt o tac cconfigurations..snoitaruginfo Copyright Goodheart-Willcox Co., Inc. 310 Essential Electrical Skills for HVACR: Theory and Labs See Figure 15-2. The indoor unit also contains a furnace when central forced warm air and air conditioning are both provided. A split system differs from a packaged unit that contains both units. 15.1.1 The Condensing Unit—Outdoor Unit A typical condensing unit wiring diagram is shown in Figure 15-3. The top section of the diagram shows a picto- rial view of the contactor, capacitor, and time delay board. A few things can be determined from the diagram. The contact configuration of the contactor is double-pole sin- gle-throw (DPST) and has a 24 Vac coil. The line side of the contacts is supplied with L1 and L2 through a disconnect box. The load side contacts feed the compressor and con- denser fan. A dual-run capacitor feeds the start windings of the PSC motors. This unit uses a time delay board to pre- vent short-cycling that can be harmful to the compressor. When the thermostat sends a cooling signal on terminal Y to the timer board, it starts a five-minute timer. After the elapsed time, 24 Vac is sent to the contactor coil. Other components shown in the condenser unit are the compressor motor, condenser motor, low-pressure switch, and high-pressure switch. Grounding the Run Capacitor The run capacitor must be grounded to the chassis with the supplied strap. The unit must be grounded in accordance with national and local codes. Safety Note Lennox Industries Inc. Control panel Heated air Compressor Ambient air Liquid line connection Suction line connection Figure 15-1. A condensing unit. Vent outlet Pressure switch Indoor blower Condensate drain connection Combustion blower Vent outlet Gas valve Burners Primary heat exchanger Secondary heat exchanger Carrier Corporation, Subsidiary of United Technologies Corp. Figure 15-2. A furnace with blower assembly.