Compressors in Air Conditioning and Refrigeration
The compressor is the central mechanical component of the vapor-compression refrigeration system. It creates the pressure difference that allows refrigerant to absorb heat in the evaporator and reject that heat in the condenser.
This section examines compressor operation from several different perspectives: what compressors do, how different compressor types work, how they are lubricated, what conditions damage them, and how a technician evaluates their mechanical pumping ability.
The lessons are arranged so that each topic builds on the material that came before it. If you are new to compressor theory, begin with Compressor Fundamentals and work through the section in order.
What You Will Learn in This Section
Explain how the compressor creates the pressure differential required for heat absorption and heat rejection.
Compare rotary, screw, scroll, centrifugal, and reciprocating compressor designs.
Follow the piston, suction valve, discharge valve, crankshaft, and connecting rod through the compression process.
Explain oil management, splash lubrication, forced lubrication, oil pumps, and net oil pressure.
Understand slugging, refrigerant migration, oil loss, high operating pressure, and other conditions that reduce compressor life.
Understand the mechanical procedure used to evaluate suction and discharge valve condition and compressor pumping ability.
Why the Compressor Is So Important
A refrigeration system depends on having both a low-pressure side and a high-pressure side. The compressor creates that pressure difference.
Low-pressure refrigerant vapor returns from the evaporator to the compressor. The compressor raises the vapor pressure and temperature and sends it toward the condenser, where the absorbed heat can be rejected.
Central Concept
The compressor creates the pressure difference that makes the vapor-compression refrigeration cycle possible.
Compressor Lessons
The seven lessons in this section progress from basic compressor theory through mechanical diagnosis.
Compressor Fundamentals
Begin with the compressor’s basic purpose, refrigerant conditions entering and leaving the compressor, liquid slugging, compression ratio, multiple-compressor systems, and the five major compressor families.
Compressor Lubrication and Oil Management
Learn why compressor oil is required, how oil provides lubrication, cooling and sealing, how oil level is observed, and why refrigeration oil must remain clean, dry, and compatible with the system.
Compressor Types
Compare rotary, screw, scroll, centrifugal, and reciprocating compressors and learn the basic mechanical method each design uses to raise refrigerant vapor pressure.
Reciprocating Compressors
Take a detailed look at pistons, cylinders, crankshafts, connecting rods, suction and discharge valves, clearance volume, hermetic and semi-hermetic construction, open-drive compressors, and shaft seals.
Compressor Lubrication Systems
Learn how oil is distributed inside compressors using splash and forced lubrication, how oil pumps work, and how crankcase pressure and pump discharge pressure are used to determine net oil pressure.
Compressor Problems and Protection
Examine liquid slugging, dirty condensers, improper refrigerant charge, refrigerant migration, oil foaming, oil loss, crankcase heaters, pump-down controls, and other conditions that can shorten compressor life.
Checking Compressor Valves and Mechanical Compressor Diagnostics
Learn how the mechanical pumping ability of a reciprocating compressor can be evaluated using pressure and vacuum readings and how suction and discharge valve problems can be identified.
How the Compressor Section Builds
Each lesson adds another layer to the compressor material.
Start with pressure difference, vapor compression, slugging, and compression ratio.
Understand compressor oil and proper oil management.
Compare the five major compressor designs.
Study the piston cycle, valves, internal parts, and housing arrangements.
Study lubrication methods, oil pumps, and net oil pressure.
Connect system problems with compressor stress, oil problems, and failure.
Finish with the mechanical procedure for evaluating suction and discharge valve condition.
Mechanical Compressor Study vs. Electrical Compressor Study
This compressor section concentrates primarily on the mechanical and refrigeration side of compressor operation.
This Section
Compressor construction, refrigerant pumping, lubrication, pressure relationships, mechanical problems, protection, and mechanical valve testing.
Electrical Course Sequence
Compressor motor windings, electrical troubleshooting, capacitors, contactors, overloads, current, voltage, and other electrical testing.
Both Are Required for Complete Diagnosis
A compressor may have a refrigeration or mechanical problem, an electrical problem, or both. A complete HVAC/R technician must eventually be able to evaluate each side separately and then combine the findings.
What You Should Know After Completing This Section
Why the compressor is necessary to the refrigeration cycle.
Why refrigerant entering the compressor should be vapor rather than liquid.
How the major compressor designs create refrigerant pressure.
How a reciprocating compressor draws in, compresses, and discharges refrigerant vapor.
Why compressor oil is necessary and how lubrication systems distribute it.
How refrigerant migration, slugging, high pressure, and lubrication problems can damage a compressor.
How the mechanical pumping ability of a reciprocating compressor can be evaluated.
The Compressor Connects the Refrigeration Cycle
The compressor is where low-pressure refrigerant vapor becomes high-pressure refrigerant vapor.
Understanding what happens inside the compressor helps explain pressure relationships, condenser operation, evaporator operation, lubrication requirements, system failures, and many later troubleshooting procedures.
Understand the compressor and much of the refrigeration system becomes easier to understand.