Compressors

Course Number: 433

This course explains the function of the compressor in a refrigeration system and introduces information on the construction and use of reciprocating, rotary, helical, scroll, and centrifugal compressors. It covers compressor motors, control, and protection, and concludes with information on preventive maintenance for compressors as well as troubleshooting and repair.

Recommended Contact Hours - 14

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.