EPA 608 Technician Certification: Low-Pressure Recovery, Evacuation, and Recharging Concepts
Importance ★★★★★ · 40% (estimate)
Overview
This chapter covers how to remove refrigerant from a low-pressure chiller and how to recharge it without damage. It explains the required evacuation level, the order for recovering liquid and vapor, how to protect the tubes from freezing, how to handle oil, and how to pressurize for small repairs.
Low-pressure appliances must be evacuated to 25 mm Hg absolute, which is about 29 inches of mercury vacuum. The level is the same with older and newer recovery equipment. Recover the liquid first, then the vapor, because a large chiller holds a lot of refrigerant as vapor. Keep water moving through the tubes or drain it so it does not freeze, and heat the oil to 130°F before draining it.
For a non-major repair, the chiller is raised to 0 psig before opening. Use heat to raise the pressure; nitrogen may be added after heat only for refrigerants that boil above 85°F, such as R-113. After reaching the required vacuum, wait a few minutes; if pressure rises, keep recovering. Recovery devices for low-pressure use commonly cut out at about 10 psig.
When recharging after evacuation, add vapor first so the water in the tubes does not freeze, and then add liquid. Centrifugal chillers are charged through the evaporator charging valve.
Key concepts
25 mm Hg absolute
The required evacuation level for low-pressure appliances before major repair or disposal, for both older and newer recovery equipment.
Memory tipLow-pressure: 25 mm Hg absolute (about 29 in. Hg vacuum).
Source: 40 CFR 82.156 Table 1 (EPA Section 608 rules) · as of 2026
Liquid, then vapor
Recover liquid first to move most of the refrigerant quickly, then recover the large amount of vapor left in the shell.
Memory tipDon't stop after the liquid.
Source: EPA Section 608 Test Topics · as of 2025
Tube freezing
As pressure drops, refrigerant gets very cold. Water in the tubes must be circulated or drained during recovery, and vapor must be charged first when recharging.
Memory tipKeep water moving; vapor first.
Source: EPA Section 608 Test Topics · as of 2025
Heating oil to 130°F
Oil holds dissolved refrigerant. Heating it to 130°F before draining drives out more refrigerant.
Memory tipWarm oil gives up refrigerant.
Source: EPA Section 608 Test Topics · as of 2025
Non-major repair pressurizing
Raise a low-pressure appliance to 0 psig before opening. Use heat. Nitrogen may be added after heat only if the refrigerant boils above 85°F at atmospheric pressure (for example R-113).
Memory tipHeat, not nitrogen, for R-11 and R-123.
Source: 40 CFR 82.156(a)(1)(ii) (EPA Section 608 rules) · as of 2026
Major repair
Removing the compressor, condenser, evaporator, or auxiliary heat exchange coil, or leaving an opening of more than 4 square inches of flow area for more than 15 minutes.
Memory tip4 sq in. for 15 minutes = major.
Source: 40 CFR 82.152 (EPA Section 608 rules) · as of 2026
Often tested
- A pressure rise after reaching the vacuum means refrigerant remains.
- Charge centrifugal chillers through the evaporator charging valve.
- Low-pressure recovery devices commonly cut out at about 10 psig.
3 sample questions
Verified practice questions from this unit.
Question 1. To what level must a low-pressure appliance be evacuated before it is opened for a major repair or disposal?
- ① 10 inches of mercury vacuum
- ② 0 psig
- ③ 25 mm Hg absolute
- ④ 4 inches of mercury vacuum
▼ Show answer and explanation▲ Hide answer and explanation
Answer: ③ 25 mm Hg absolute
Key point: Low-pressure appliances: 25 mm Hg absolute
Table 1 in 40 CFR 82.156 requires low-pressure appliances to be evacuated to 25 mm Hg absolute, which is a deep vacuum of about 29 inches of mercury.
Wrong choices
- 10 inches of mercury vacuum: 10 inches applies to some large high- and medium-pressure appliances.
- 0 psig: 0 psig is for non-major repairs.
- 4 inches of mercury vacuum: 4 inches applies to small appliances and older equipment on some appliances.
Question 2. During refrigerant recovery from a chiller, why should water be circulated through the tubes or drained?
- ① To add moisture to the refrigerant
- ② To keep the purge unit running
- ③ To keep the water in the tubes from freezing
- ④ To speed up the compressor
▼ Show answer and explanation▲ Hide answer and explanation
Answer: ③ To keep the water in the tubes from freezing
Key point: Keep water moving to prevent tube freezing
As pressure drops during recovery, the refrigerant gets very cold. If water sits still in the tubes it can freeze and burst them, so water should be circulated or drained during evacuation.
Wrong choices
- To add moisture to the refrigerant: Moisture in refrigerant is unwanted.
- To keep the purge unit running: It is not done to run the purge unit.
- To speed up the compressor: This step protects the tubes; it is not for the compressor.
Question 3. When recovering refrigerant from a low-pressure chiller, what should be removed first?
- ① The liquid refrigerant
- ② The water in the tubes
- ③ The vapor
- ④ The oil
▼ Show answer and explanation▲ Hide answer and explanation
Answer: ① The liquid refrigerant
Key point: Low-pressure recovery: liquid first, then vapor
Recovering liquid first speeds up the job because most of the refrigerant is liquid. After the liquid is out, the remaining vapor must also be recovered.
Wrong choices
- The water in the tubes: Water in the tubes should keep moving or be drained to prevent freezing; it is not recovered first.
- The vapor: Vapor is recovered after the liquid.
- The oil: Oil is not recovered first.
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.