Air Conditioning and Refrigeration Technology > Control Systems

Control Systems

Course Number: 437

The Control Systems textbook introduces the need for control and control methods, including information on self-powered, pneumatic, hydraulic, electric, and electronic systems. It covers various sensors and controlled devices, the basics of two-position, floating, and proportional control systems and their maintenance and troubleshooting, and the various processes requiring control in a refrigeration or air-conditioning system.

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Recommended Contact Hours – 10

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Table of Contents

Chapter 1: Introduction to Control Systems

Topics: Automatic control; Control system basics; Two-position, floating, and proportional control; Open- and closed-loop control; Operating power

Learning Objectives:

  • Explain why control systems are needed and name devices used to control environmental conditions.
  • Define the terms used to describe control systems-controlled variable, controller, controlled device, setpoint, control point, and controlled medium-and name the basic elements of a control system.
  • Describe the action of two-position, floating, and proportional control.
  • Explain how anticipators work.
  • Compare open-loop and closed-loop control.
  • Compare the basic requirements of pneumatic/hydraulic control systems to those of electric/electronic control systems.

Chapter 2: Sensors and Controlled Devices

Topics: Temperature, humidity, and pressure sensors; Dampers; Valves; Variable-speed drives

Learning Objectives:

  • Explain the need for a sensor in a control system.
  • Name and explain the operation of three kinds of temperature sensors.
  • Define relative humidity, state the range required for human comfort, and describe common humidity sensors.
  • Name three common pressure sensors and explain their operation.
  • Explain the operation of two-position dampers and valves in shutoff and throttling applications.
  • List the advantages of variable-speed drives over older methods of speed control.

Chapter 3: Automatic Control Systems

Topics: Two-position, floating, and proportional electric control; Pneumatic systems, controllers, actuators, relays, and switches; Electronic systems; Proportional band, gain, and PID control

Learning Objectives:

  • Describe the operation of two-position, floating, and proportional electric controllers.
  • List the equipment needed for a pneumatic control system.
  • Name several pneumatic relays and switches, and explain why each is used.
  • Discuss the advantages and basic operation of electronic controls.
  • Define resolution, sensitivity, proportional band, and gain, and explain how they are related.
  • Distinguish between integral and derivative action, and explain how each can improve system performance.

Chapter 4: Control of Refrigeration and Air-Conditioning Processes

Topics: Primary control; Low-pressure, high-pressure, and high-temperature controls; Anti-recycle timers; Pressure regulators; Oil-level controls; Overload protection; Capacity control

Learning Objectives:

  • Explain how pumpdown control operates and why pumpdown is often preferred over other methods of primary control.
  • Describe the location, function, and operation of a high-pressure control.
  • Name three ways to control condenser pressure and at least three ways to control system capacity.
  • Explain how a differential oil pressure safety control works.
  • Compare the two methods of modulating the flow of water to hydronic terminals.

Chapter 5: Maintaining and Troubleshooting Controls

Topics: Maintaining pressure controls, thermostats, switches, valves, timers, controllers, relays, and power supplies; Troubleshooting the system

Learning Objectives:

  • List the four basic steps involved in setting up a PM program.
  • Explain the importance of high-pressure controls as safety devices and explain their testing procedures.
  • Explain how oil pressure is maintained in various kinds of compressors.
  • Describe the testing and maintenance required for condenser water regulating valves and compressor capacity controls.
  • Explain how to check for oil and water contamination in control air and what measures to take to minimize them.
  • Explain the major maintenance requirements of a pneumatic control system.
  • Describe the maintenance required by electric and electronic controllers.
  • Explain how to use a troubleshooting chart.

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