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EPA 608 Technician Certification: Refrigeration Cycle, Gauges, and the Three Rs Concepts

Importance ★★★★☆ · 25% (estimate)

Overview

This chapter reviews how a refrigeration system moves heat and how technicians measure and handle the refrigerant in it. You will follow the refrigerant around the cycle, read manifold gauges, change gauge pressure to absolute pressure, and learn the difference between recover, recycle, and reclaim.

The compressor squeezes low-pressure vapor into high-pressure vapor. In the condenser the vapor gives off heat and becomes a high-pressure liquid. The metering device drops the pressure, and in the evaporator the low-pressure refrigerant boils and absorbs heat. It returns to the compressor as a low-pressure vapor. The part from the compressor to the metering device is the high side; the rest is the low side.

On a manifold, the blue compound gauge and hose connect to the low side, the red gauge and hose to the high side, and the yellow center hose to the recovery machine, vacuum pump, or cylinder. A compound gauge reads both pressure and vacuum. To change gauge pressure (psig) to absolute pressure (psia), add 14.7.

To recover is to remove refrigerant and store it. To recycle is to clean it for reuse by the same owner. To reclaim is to bring it to new-product purity and prove it by testing. Shorter, wider hoses speed recovery, and refrigerants must never be mixed. After a repair, the system is evacuated to remove air and moisture before charging.

Key concepts

  • Compressor

    The part that draws in low-pressure refrigerant vapor and pumps it out as high-pressure, high-temperature vapor.

    Memory tipLow-pressure vapor in, high-pressure vapor out.

  • Condenser

    The coil where high-pressure vapor gives off heat and condenses into a high-pressure liquid.

    Memory tipHeat out, vapor becomes liquid.

  • Metering device

    The part, such as an expansion valve or capillary tube, that drops the refrigerant's pressure before it enters the evaporator.

    Memory tipHigh side ends here; low side begins.

  • Evaporator

    The coil where low-pressure liquid refrigerant boils into vapor and absorbs heat from the air or water being cooled.

    Memory tipHeat in, liquid becomes vapor.

  • Manifold gauge colors

    Blue gauge and hose for the low side, red for the high side, and yellow for the center hose to the recovery machine, vacuum pump, or cylinder.

    Memory tipBlue low, red high, yellow center.

    Source: EPA Section 608 Test Topics · as of 2025

  • psig and psia

    Gauge pressure (psig) reads zero at normal air pressure. Absolute pressure (psia) counts from a perfect vacuum, so psia equals psig plus 14.7.

    Memory tipAdd 14.7 to go from psig to psia.

    Source: EPA Section 608 Test Topics · as of 2025

  • Recover, recycle, reclaim

    Recover: remove and store. Recycle: clean for reuse by the same owner without full testing. Reclaim: reprocess to AHRI 700-based purity and verify by analysis.

    Memory tipOnly reclaimed refrigerant may go to a new owner.

    Source: 40 CFR 82.152 (EPA Section 608 rules) · as of 2026

See it in a picture

Refrigeration loop: compressor on the right, condenser at the top with heat out, metering device on the left, evaporator at the bottom with heat in. Labels show high-pressure vapor, high-pressure liquid, low-pressure liquid plus vapor, and low-pressure vapor. A dashed line splits high and low sides.
Refrigerant states around the refrigeration cycle

Often tested

  • The evaporator absorbs heat; the condenser gives it off.
  • Refrigerant leaves the condenser as a high-pressure liquid.
  • Refrigerant enters the compressor as a low-pressure vapor.
  • Dehydration evacuation removes air and moisture before charging.
  • Air (noncondensables) in a system raises head pressure.
  • Never mix different refrigerants in one recovery cylinder.

3 sample questions

Verified practice questions from this unit.

Practice questionReviewedCore › Refrigeration Cycle, Gauges, and the Three Rs★★★★☆

Question 1. Look at the picture. Arrows show the direction of refrigerant flow, and part A squeezes low-pressure vapor into high-pressure vapor. What is part B?

Refrigeration loop with arrows showing flow. Circle A on the right sends refrigerant up into box B at the top. From B the line runs down the left side to a small diamond C, then into box D at the bottom, then back up to A.
  1. ① Condenser
  2. ② Accumulator
  3. ③ Metering device
  4. ④ Evaporator
▼ Show answer and explanation▲ Hide answer and explanation

Answer: ① Condenser

Key point: After the compressor comes the condenser

Part A is the compressor. Following the arrows, the hot high-pressure vapor goes next to part B, the condenser, where it gives off heat and becomes a liquid. Then comes the metering device (C) and the evaporator (D).

Wrong choices

  • Accumulator: An accumulator would be in the suction line before the compressor, and it is not shown.
  • Metering device: The metering device is the small part where pressure drops (part C).
  • Evaporator: The evaporator is where low-pressure refrigerant absorbs heat; it comes after the metering device (part D).
Practice questionReviewedCore › Refrigeration Cycle, Gauges, and the Three Rs★★★★☆

Question 2. In which part of a refrigeration system does the refrigerant absorb heat from the space being cooled?

  1. ① Receiver
  2. ② Evaporator
  3. ③ Condenser
  4. ④ Compressor
▼ Show answer and explanation▲ Hide answer and explanation

Answer: ② Evaporator

Key point: Evaporator absorbs heat; condenser rejects heat

In the evaporator, low-pressure liquid refrigerant boils into vapor and absorbs heat from the air or water around it. That heat is later given off in the condenser.

Wrong choices

  • Receiver: The receiver stores liquid refrigerant.
  • Condenser: The condenser gives off heat to the outside.
  • Compressor: The compressor raises the pressure of the vapor; it does not cool the space.
Practice questionReviewedCore › Refrigeration Cycle, Gauges, and the Three Rs★★★★☆

Question 3. What does it mean to "recover" refrigerant?

  1. ① Clean it with filter-driers for reuse by the same owner
  2. ② Release it slowly to the air
  3. ③ Remove it from a system and store it in an outside container, without testing or processing it
  4. ④ Clean it to meet the new-refrigerant purity standard
▼ Show answer and explanation▲ Hide answer and explanation

Answer: ③ Remove it from a system and store it in an outside container, without testing or processing it

Key point: Recover = remove and store, no processing

To recover is to remove refrigerant in any condition from an appliance and store it in an external container, without necessarily testing or processing it.

Wrong choices

  • Clean it with filter-driers for reuse by the same owner: Cleaning for reuse is recycling.
  • Release it slowly to the air: Releasing refrigerant is venting, which is illegal.
  • Clean it to meet the new-refrigerant purity standard: Meeting the purity standard is reclaiming.
Practice 5 questions from this unit →

AI-written · Verified · Written by AI. Only units that passed a separate AI check (re-reading facts and numbers) are published. Tell us if you find a mistake.