10.3 Type III Recovery and Procedures

The Recovery Standard for Low-Pressure Systems

Type III recovery is governed by one number you must commit to memory: the required evacuation level. Before a major repair or disposal of a low-pressure appliance, the technician must reduce the system to a deep vacuum. Unlike the higher-pressure classes, the target does not change with the age of the recovery equipment:

25 mm Hg absolute is a near-complete evacuation — only 25 mm of mercury above a perfect vacuum. Read it on a micron (absolute) gauge, never a compound gauge. The notorious exam trap is confusing 25 mm Hg absolute with 25 in. Hg vacuum: 25 mm Hg absolute is about 0.98 in. Hg absolute (roughly 28.9 in. Hg vacuum), while 25 in. Hg vacuum leaves about 4.9 in. Hg (about 125 mm Hg) absolute — roughly five times the absolute pressure of the real target. The same 25 mm Hg absolute level applies before disposing of a low-pressure appliance.

Pressure References You Must Keep Straight

Type III is the only section that mixes vacuum scales, so anchor these reference points:

The Freezing Hazard — Keep Water Flowing

Here is the procedure point the exam loves. As you pull a vacuum, the remaining liquid refrigerant boils violently at the low pressure and absorbs heat from the water tubes. If the cooling and chilled-water pumps are off, that heat is drawn from the now-stagnant water, which can freeze and rupture the evaporator or condenser tubes. The rule: keep water circulating through the tubes during recovery — or drain the water from the tubes — so it cannot freeze; moving water also feeds heat to vaporize the refrigerant. Stop the water and you risk thousands of dollars in burst-tube damage.

Recovery Procedure and Pressurization Limits

A typical low-pressure recovery sequence:

1. Prepare — shut down the chiller, let pressures equalize, connect recovery equipment, and stage enough recovery cylinders (charges are often hundreds of pounds).
2. Keep water flowing (or drain it) — circulate condenser and chilled water, or remove it from the tubes, to prevent tube freezing.
3. Liquid recovery — transfer liquid from the shells first; low-pressure refrigerant is easy to handle as a liquid because it boils so high.
4. Vapor recovery — pull the remaining vapor with the recovery machine; apply gentle heat to the shells to vaporize the last liquid.
5. Reach the target — continue until 25 mm Hg absolute is achieved (with recovery equipment of any age).
6. Verify — isolate, wait a few minutes, and read the final level on a micron/absolute gauge. If the pressure rises back above the target, liquid refrigerant remains in the system or the oil, so keep recovering.
7. Oil — if oil must be drained, heat it to 130 °F first so less refrigerant leaves with it.

Pressurizing a Low-Pressure Machine

Raise the pressure of a low-pressure chiller only with EPA's preferred methods and within the manufacturer's limits. For a leak test, EPA's order of preference is controlled hot water or a built-in heating/pressurization device (such as Prevac) first, then nitrogen — never air or oxygen. Stay below the rupture-disc rating, which is set at the chiller's maximum working pressure (Trane, for example, rates the disc on its R-123 CenTraVac chillers at 15 psig ±2 psig), or the disc can burst and vent the charge.

For a non-major repair that will not be followed by evacuation, the appliance must be pressurized to no higher than 0 psig before it is opened, with openings covered when isolation is not possible. On machines whose refrigerant boils at or below 85 °F (R-11, R-123), use heat only — methods such as nitrogen that require later purging are not allowed; on R-113 machines, use heat as far as possible and nitrogen only to bring the pressure the rest of the way to atmospheric.

Example: A technician recovering a 700-lb R-123 charge wants to "speed things up" by pushing nitrogen into the machine and lets the gauge climb toward the rupture-disc rating. The disc lets go, venting nitrogen and refrigerant and forcing a costly disc replacement. The correct method is to recover with the machine — liquid first, then vapor — while water keeps moving through the tubes, and never to use nitrogen to push the charge out.

For the Exam: Recover to 25 mm Hg absolute with recovery equipment of any age (25 mm Hg absolute, not 25 in. Hg). Keep water circulating or drain the tubes to prevent freezing. Heat oil to 130 °F before draining it. Recharge vapor before liquid, through the evaporator charging valve. For leak tests, raise pressure with hot water or a built-in heater first, then nitrogen, below the rupture-disc rating. Verify the vacuum on a micron gauge after the system stabilizes.