EPA 608 Technician Certification Low-Pressure Recovery, Evacuation, and Recharging Summary

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.

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.

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.

Under a deep vacuum, liquid refrigerant would boil and become very cold, which can freeze water in the tubes. Charge vapor first until the pressure is high enough (above the saturation pressure for 32°F), and then add liquid.

Wrong choices

• Liquid refrigerant: Adding liquid first under a deep vacuum can make it boil and freeze the water in the tubes.
• Nitrogen: Nitrogen is not used to start charging.
• Oil: Oil is not added first in place of refrigerant.

A large chiller has a big volume, so a significant amount of refrigerant stays as vapor after the liquid is removed. EPA's test topics stress the need to recover vapor in addition to liquid.

Wrong choices

• Vapor contains only air: The vapor is mostly refrigerant, not just air.
• Vapor can be vented legally from low-pressure systems: Venting refrigerant vapor is illegal.
• The rupture disc needs vapor to stay closed: This is not why vapor is recovered.

Refrigerant dissolves in oil. EPA's test topics say to heat the oil to 130°F before removing it, which drives out more refrigerant so less is lost with the oil.

Wrong choices

• 212°F: 212°F is too hot and is not the guideline.
• 32°F: Cold oil holds more refrigerant.
• 70°F: 70°F leaves more refrigerant dissolved in the oil.

EPA's test topics say centrifugal chillers are charged through the evaporator charging valve, starting with vapor until the pressure is high enough to add liquid safely.

Wrong choices

• The condenser water drain: The water drain is not part of the refrigerant circuit.
• The rupture disc: The rupture disc is a safety device, not a valve.
• The purge unit vent: The purge vent is not a charging connection.

EPA's test topics say to wait a few minutes after reaching the required vacuum. If pressure rises, liquid refrigerant or refrigerant in the oil remains, so recovery should continue.

Wrong choices

• Open the chiller right away: Opening now would release refrigerant.
• Stop, because the pressure rise means the job is done: A pressure rise means refrigerant is still there.
• Add nitrogen and vent it: Venting is illegal.

In Table 1, the level for low-pressure appliances is 25 mm Hg absolute in both columns: equipment made before and on or after November 15, 1993.

Wrong choices

• Yes; older equipment needs only 0 psig: 0 psig is for non-major repairs.
• Yes; older equipment needs only 4 inches of mercury vacuum: 4 inches applies to some medium- and high-pressure appliances with older equipment, not low-pressure ones.
• Yes; older equipment needs 15 inches of mercury vacuum: 15 inches is for large medium-pressure appliances with newer equipment.

Under 40 CFR 82.156(a)(1)(ii), low-pressure appliances are pressurized to 0 psig before opening for a non-major repair. For refrigerants that boil above 85°F (such as R-113), use heat first and then nitrogen if needed. For refrigerants that boil at or below 85°F (such as R-11 and R-123), methods such as nitrogen that need later purging may not be used.

Wrong choices

• Leave it in a vacuum and open it: Opening under vacuum draws in air and moisture; the rule requires 0 psig.
• Use compressed air: Compressed air is not an allowed method.
• Use nitrogen only, with no heat: The rule says heat must be used first to raise pressure as much as possible.