4.2 System Components in Detail

EPA 608 Technician Certification Exam

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1 Introduction to EPA 608 Certification

1.1 What EPA 608 Is and Who Needs It 1.2 Exam Format, Scoring, and Administration 1.3 How to Study for EPA 608

2 Regulations and the Clean Air Act

2.1 Clean Air Act Overview 2.2 Penalties and Enforcement 2.3 Montreal Protocol and International Agreements 2.4 AIM Act and HFC Phasedown Schedule 2.5 SNAP Program and Refrigerant Transitions

3 Refrigerants and Ozone Science

3.1 The Science of Ozone Depletion (ODP and GWP) 3.2 Refrigerant Classification, ASHRAE Numbering, and Safety Groups 3.3 Common Refrigerants: Properties, Applications, and Phaseout Status 3.4 Refrigerant Blends: Glide, Fractionation, and Liquid Charging

4 The Refrigeration Cycle

4.1 The Basic Refrigeration Cycle 4.2 System Components in Detail 4.3 Heat Transfer and Pressure-Temperature Relationships

5 Refrigerant Safety and Handling

5.1 Refrigerant Hazards and Health Effects 5.2 Safe Handling Practices, PPE, and Cylinders 5.3 A2L (Mildly Flammable) Refrigerant Safety

6 Recovery, Recycling, and Reclaiming

6.1 The Three Rs: Recover, Recycle, Reclaim 6.2 Recovery Equipment Requirements 6.3 Required Levels of Evacuation 6.4 Refrigerant Sales Restrictions and Recordkeeping

7 Leak Detection and Repair

7.1 Leak Detection Methods 7.2 Leak Repair Requirements and Trigger Rates 7.3 Leak-Rate Calculation, Recordkeeping, and Reporting

8 Type I — Small Appliances

8.1 What Counts as a Small Appliance 8.2 Type I Recovery Requirements 8.3 Type I Procedures, Access Valves, and the Open-Book Exam

9 Type II — High-Pressure Appliances

9.1 What Type II Covers: High-Pressure System Overview 9.2 Type II Recovery Methods and Required Evacuation Levels 9.3 Leak Detection, the Repair Triggers, and Recordkeeping 9.4 The R-22 Phaseout, Retrofits, and the Move to Lower-GWP A2Ls

10 Type III — Low-Pressure Appliances

10.1 Low-Pressure System Fundamentals 10.2 Purge Units and Air Management 10.3 Type III Recovery and Procedures 10.4 Type III Leak Testing

11 10. Disposal, Shipping, and Compliance

11.1 Equipment Disposal Requirements 11.2 Refrigerant Shipping and Transport 11.3 Compliance Checklist and Best Practices

12 Final Review and Exam Strategy

12.1 High-Yield Core Section Review 12.2 Type I vs Type II vs Type III: Side-by-Side Review 12.3 How the Exam Works and Exam-Day Strategy

4.2 System Components in Detail

Key Takeaways Explain This Topic AI

Compressor types include reciprocating (pistons), scroll (two spirals), screw (meshing rotors), centrifugal (impeller, used in large Type III chillers), and rotary/vane (small appliances).

Metering devices: TXV/EEV modulate flow to control superheat; capillary tubes and fixed orifices/pistons deliver a fixed flow regardless of load.

Filter-driers remove moisture and particulates and should be replaced whenever a system is opened; sight-glass indicator green = dry, yellow = wet.

The accumulator (suction line) protects the compressor from liquid slugging; the receiver (liquid line) stores excess liquid for the metering device.

Oil circulates with the refrigerant to lubricate, seal, and cool the compressor; proper oil-refrigerant miscibility is required so oil returns to the compressor.

Last updated: June 2026

The four major components define the cycle, but real equipment contains many secondary parts that the EPA 608 exam tests across every Type section. Knowing what each part does — and where it sits in the loop — lets you answer service, recovery, and safety questions with confidence.

Compressor Types

The compressor is the most expensive and most frequently tested component. Different designs suit different capacities, and the exam connects compressor type to appliance category (especially centrifugal for Type III).

Type How It Works Common Applications Key Feature

Reciprocating Pistons compress vapor in cylinders Commercial refrigeration, residential AC Most common in small–medium systems

Scroll Two spiral scrolls orbit to trap and squeeze vapor Residential/light commercial AC, heat pumps Quiet, efficient, few moving parts

Screw (helical rotary) Two meshing helical rotors compress vapor Large commercial, industrial High capacity, continuous flow

Centrifugal Impeller spins at high speed using centrifugal force Large chillers (100+ tons) Highest capacity; used in Type III low-pressure systems

Rotary (vane) Vanes in a rotating drum compress vapor Window ACs, small refrigerators Compact, lightweight

A memory hook: small appliances use rotary; homes and light commercial use scroll or reciprocating; giant low-pressure chillers use centrifugal. That last pairing — centrifugal with Type III — appears repeatedly.

Metering (Expansion) Devices

The metering device sets how much liquid feeds the evaporator. There are two families: modulating valves that adjust to the load, and fixed restrictions that do not.

Device Type How It Controls Flow Notes

Thermostatic expansion valve (TXV/TEV) Modulating A sensing bulb on the evaporator outlet senses temperature and adjusts the valve to hold a target superheat Most efficient; maintains superheat across varying loads

Electronic expansion valve (EEV) Modulating A controller and stepper motor adjust the orifice electronically Precise; common on modern variable-capacity systems

Capillary tube Fixed Long, thin tube provides constant restriction No moving parts; cheap; critical charge

Fixed orifice / piston Fixed A set-diameter hole meters a constant flow Simple, low cost; flow does not adapt to load

The big exam distinction: a TXV adjusts refrigerant flow to maintain superheat as load changes, while capillary tubes and fixed orifices deliver the same flow regardless of load. That adaptability is the TXV's main advantage and a frequent test point.

Condenser and Evaporator Variants

Condensers are air-cooled (most residential), water-cooled (cooling tower or once-through), or evaporative . All reject the heat that the evaporator absorbed plus the compressor's work.

Evaporators are direct-expansion (DX) coils in most AC, or flooded evaporators in large chillers. The evaporator is always the cold, low-pressure heat-absorbing coil.

Accessories That Show Up on the Exam
Filter-Drier

Function: Removes moisture and particulates from the refrigerant.

Location: Liquid line, between the condenser and the metering device.

Why it matters: Moisture forms acids that corrode internal parts, and can freeze at the metering device (“icing”), blocking flow. Replace the filter-drier whenever the system is opened for service.

Sight Glass / Moisture Indicator

Location: Liquid line, usually just after the filter-drier.

Clear glass: Properly charged, full liquid flow.

Bubbles: Possible undercharge, restriction, or low subcooling.

Green dot = dry (acceptable moisture); Yellow dot = wet (excess moisture, needs attention).

Accumulator

Function: Catches liquid leaving the evaporator and lets it boil off before it reaches the compressor — prevents liquid slugging.

Location: Suction line, between the evaporator and compressor.

Common in: Heat pumps, which reverse flow direction.

Receiver

Function: Stores liquid refrigerant after the condenser and ensures a solid column of liquid feeds the metering device.

Location: Liquid line, between the condenser and metering device.

Key fact: Receivers require pressure-relief protection.

Service Valves and Pressure-Safety Devices

Suction service valve / discharge service valve: On the compressor low- and high-side connections.

Schrader valve: Spring-loaded service port (like a tire valve); the hose core depressor opens it.

King valve: At the receiver outlet; lets you isolate the charge in the condenser and receiver.

Safety Device Function Reset
Pressure relief valve (PRV) Opens at a set pressure to relieve over-pressure Reseats automatically (reusable)
Rupture (burst) disc Bursts at a set pressure One-time — replace after it activates
Fusible plug Melts at a set temperature One-time — replace after it activates

Never valve off or bypass a pressure-relief device while the system is operating.

The Role of Oil

Refrigerant systems carry lubricating oil that circulates with the refrigerant . The oil lubricates compressor bearings and moving parts, seals the compression chamber against leakage, and helps carry heat away from the compressor.

For the oil to do its job, it must have proper miscibility with the refrigerant — it must mix and travel with it. If oil and refrigerant do not mix well, oil pools in the evaporator and suction line and starves the compressor; if they mix too freely, the oil film thins and lubrication fails. This is why a refrigerant change often requires changing the oil type (for example, mineral oil for older CFC/HCFC systems versus POE oil for HFC systems).

Worked Example: A technician opens a residential R-410A system to replace a failed TXV. Because the sealed loop was exposed to atmosphere, moisture and air entered. Best practice: install a new filter-drier in the liquid line, evacuate the system to remove moisture and non-condensables, then recharge. After running, the sight glass shows a green dot and clear liquid — confirming the drier captured moisture, the charge is correct, and the TXV is feeding the evaporator properly. Skipping the new drier would risk acid formation and metering-device icing.

For the Exam: Centrifugal compressors serve large Type III chillers. TXVs modulate flow to hold superheat; fixed orifices and cap tubes do not. Replace the filter-drier whenever the system is opened. Green = dry, yellow = wet. Accumulators (suction line) stop slugging; receivers (liquid line) store liquid. PRVs reseat; rupture discs and fusible plugs are one-time use.