Compressors

Table of Contents

Chapter 1: Introduction to Compressors

Topics: Open and hermetic compressors; Reciprocating, rotary, helical, scroll, and centrifugal compressors; Multiple compressor applications; Replacement

Learning Objectives:

• List the five kinds of air conditioning and refrigeration compressors.
• Contrast the operation of positive-displacement and kinetic-displacement compressors.
• Explain how each kind of the five kinds of compressor raises the pressure of the refrigerant vapor.
• Define staging and cascading and explain why each is used.
• List important considerations in compressor replacement.

Chapter 2: Reciprocating Compressors

Topics: Reciprocating compressor housings, pistons, rods, crankshafts, bearings, seals, oil pumps, cylinder heads, and valves; Vibration control

Learning Objectives:

• Describe the general construction of open, semi-hermetic, and full-hermetic reciprocating compressors.
• Explain how the basic parts of a reciprocating compressor are assembled.
• Identify common designs of housings, pistons, connecting rods, crankshafts, bearings, seals, cylinder heads, and valves used in reciprocating compressors.
• Explain how a cylinder unloader controls the capacity of a reciprocating compressor.
• Explain how compressors are lubricated.
• Explain how compressor vibration and noise are controlled.

Chapter 3: Rotary, Helical, and Scroll Compressors

Topics: Rotary compressor advantages; Rotary vane, helical, and scroll compressors; Accumulators; Bearings; Lubrication

Learning Objectives:

• Describe the operation of single-vane and multiple-vane rotary compressors, including how each raises refrigerant pressure.
• List several advantages of rotary compressors over reciprocating compressors.
• Define slugging and cavitation.
• Tell the two functions of an accumulator in a rotary compressor.
• Compare and contrast rotary and helical compressors.
• Describe the operation of the single-screw and twin-screw helical compressor.
• Describe the operation of a scroll compressor.

Chapter 4: Centrifugal Compressors

Topics: Centrifugal compressor characteristics, construction, bearings, lubrication, and purging; Capacity control; Compressor repair

Learning Objectives:

• Describe the operating principle of a kinetic-displacement compressor.
• List advantages and disadvantages of centrifugal compressors as compared to positive-displacement types.
• Explain reverse hydrostatic sealing.
• Explain how centrifugal compressors deal with thrust forces.
• Trace the operation of a typical centrifugal compressor lubrication system.
• Tell the purpose of a purge system.
• Describe the capacity control methods used in centrifugal compressors.

Chapter 5: Compressor Motors

Topics: Basic requirements; Single-phase, split-phase, capacitor, dual-voltage, repulsion, and three-phase motors; Starting switches

Learning Objectives:

• Explain the basic requirements of a compressor motor.
• Name the different types of single-phase and three-phase motors used to power compressors and tell which ones can be used in hermetic compressors.
• Explain how to reverse the direction of rotation of a motor.
• Explain how to change voltages on a dual-voltage motor.
• Describe the operation of the current and potential relays used for starting single-phase hermetic compressor motors.

Chapter 6: Compressor Control and Protection

Topics: Motor starting devices; Overload protection; High-pressure and low-pressure protection; Oil-pressure safety switches; Crankcase heaters

Learning Objectives:

• Name the two basic categories of motor-starting devices and tell how each operates.
• Explain the function of a reduced-voltage starter and name the five kinds used with compressor motors.
• Describe the three kinds of motor overload protection commonly used with compressor motors.
• Discuss the causes of, effects of, and solutions for high discharge pressure, low suction pressure, and low oil pressure.
• Explain the function of a suction-line accumulator.
• Explain why crankcase heaters are sometimes necessary.
• Explain how heat exchangers improve the performance of a compressor.

Chapter 7: Compressor Maint., Troubleshooting, & Repair

Topics: Importance of PM; Common mechanical problems; Repair basics; Disassembling, cleaning, inspecting, and reassembling compressors

Learning Objectives:

• State the first rule of preventive maintenance for compressors and related components.
• List preventive maintenance procedures common to most compressors.
• Explain how to calculate voltage imbalance in a three-phase motor.
• Name at least three possible causes of a low compressor oil level.
• Name at least three possible causes of compressor overheating.
• Explain how electrical problems can cause various system malfunctions
• Explain how to pump down a compressor for repairs.
• Describe compressor disassembly, cleaning, inspection, and reassembly procedures.
• Describe motor spot burnouts and cookouts, list their possible causes, and explain how to determine the severity of a burnout.
• Explain how to clean up a system after a motor burnout.

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