Level 1, Unit 6, Section 1 – Compressors

Unit 6 — Refrigeration System Components

Section 1 — Compressors

Section 1 Overview

The compressor is the heart of every vapour compression refrigeration system — and the most expensive component to replace. This section develops the compressor knowledge required of Level 1 Refrigeration and Air Conditioning Mechanics (313A/313D): the four critical functions the compressor performs, how it is lubricated and cooled, and how to recognize the failure modes that end compressor life prematurely.

1.0.1 — General Learning Outcomes

Upon successful completion of this section, the apprentice will be able to:

Describe the four critical functions of the compressor — maintaining pressure differential, circulating refrigerant, adding heat of compression, and removing vapour from the evaporator — and explain how each function sustains the vapour compression cycle.
Identify the major compressor oil types (mineral, alkylbenzene, POE, PAG, PVE), match each to its compatible refrigerants, compare splash and pressure lubrication methods, and describe the oil management practices that protect compressor reliability in the field.
Measure and interpret suction superheat, subcooling, and discharge temperature; explain why each parameter matters for system and compressor health; and identify the five methods of compressor cooling and the conditions under which each is applied.
Recognize the common compressor failure modes — motor winding failure, contactor failure, flood back, flood start, lubrication failure, mechanical failure, and off-cycle refrigerant migration — and describe the causes, symptoms, and remedies for each.

1.0.2 — Section 1 — Lessons at a Glance

Section 1 builds from the fundamental functions the compressor performs through the lubrication, cooling, and failure analysis skills applied on every compressor service call.

1.1

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Compressor’s Critical Functions

The four interdependent functions the compressor performs — maintaining pressure differential, circulating refrigerant, adding heat of compression, and removing vapour from the evaporator — and how each sustains the refrigeration cycle.

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1.2

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Methods of Compressor Lubrication

Oil charge and oil types (mineral, AB, POE, PAG, PVE); the five functions of compressor oil; splash vs. pressure lubrication; and the oil management practices — level monitoring, oil return, temperature, contamination — that protect compressor life.

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1.3

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Methods of Compressor Cooling

Measuring and interpreting suction superheat, subcooling, and discharge temperature. The five cooling methods — suction gas, air, water, liquid injection, and oil cooling — and which compressor types depend on each to prevent overheating and motor damage.

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1.4

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Common Compressor Failures

Motor winding failure, contactor failure, flood back, flood start, lubrication failure, mechanical failure (valves, bearings, pistons, shaft seals), and off-cycle refrigerant migration — causes, symptoms, remedies, and prevention for each failure mode.

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1.0.3 — Why Compressors Matter in HVAC/R

Every vapour compression refrigeration system depends on the compressor to create and maintain the pressure difference that drives heat transfer. Without a functioning compressor, refrigerant cannot circulate, evaporator temperatures cannot be maintained, and the system produces no cooling effect. The compressor is also the component most likely to fail catastrophically — and the most expensive to replace.

A technician who understands how the compressor is lubricated, how it sheds heat, and how it fails can prevent most compressor losses through proper installation and maintenance. When a compressor does fail, that understanding enables accurate diagnosis and correct selection of the replacement — rather than repeating the failure.

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How Section 1 Connects to the Rest of Unit 6

Section 1 establishes the compressor as the pressure boundary between the high side and low side of the refrigerant circuit. This boundary is the reference point for every other component covered in Unit 6: the valves (Section 2–3) that meter refrigerant across it and the accessory devices (Section 4) that protect it.

The lubrication and cooling concepts in this section also connect directly to refrigerant handling (Unit 2) — oil type must match the refrigerant — and to the electrical fundamentals in Unit 4, where motor winding protection and control logic are introduced.