2 Evacuation Levels and Verification

Purpose and pressure measurements

Evacuation removes refrigerant from an appliance before it is opened or disposed of. The required recovery endpoint depends on the appliance’s pressure class, full charge, age, and the recovery equipment used. These endpoints are not the deeper vacuum used to dehydrate a repaired system before charging.

For the stationary-appliance requirements below, inches of mercury (in. Hg) indicate vacuum relative to standard atmospheric pressure of $29.9$ in. Hg. A higher vacuum number means lower system pressure. The low-pressure appliance value is instead an absolute pressure.

Stationary appliance evacuation levels

For most stationary appliances other than small appliances, motor-vehicle air conditioners (MVACs), and MVAC-like appliances, the required levels are:

• Very-high-pressure appliance: $0$ in. Hg vacuum, whether the recovery equipment was made before November 15, 1993, or on or after that date.

• High-pressure appliance with a full charge below $200$ lb: $0$ in. Hg vacuum for either equipment date category.

• High-pressure appliance with a full charge of $200$ lb or more: $4$ in. Hg vacuum with equipment made before November 15, 1993; $10$ in. Hg vacuum with equipment made on or after that date.

• Medium-pressure appliance with a full charge below $200$ lb: $4$ in. Hg vacuum with equipment made before November 15, 1993; $10$ in. Hg vacuum with equipment made on or after that date.

• Medium-pressure appliance with a full charge of $200$ lb or more: $4$ in. Hg vacuum with equipment made before November 15, 1993; $15$ in. Hg vacuum with equipment made on or after that date.

• Low-pressure appliance: $25$ mm Hg absolute for either equipment date category.

Do not confuse $25$ mm Hg absolute with $25$ mm Hg vacuum. The table excludes small appliances, MVACs, and MVAC-like appliances. Small-appliance rules use recovery percentages or a specified alternative evacuation endpoint. Appliance age can also affect particular requirements and exceptions, so consult the applicable regulation for the job.

Measuring and verifying evacuation

A compound manifold gauge indicates pressure relative to local atmospheric pressure. Its vacuum scale reads in. Hg vacuum, and its positive-pressure scale typically reads psig. Use a suitable, functioning gauge and read it while the appliance or isolated section is connected to the recovery equipment.

For a low-pressure appliance, use an instrument capable of measuring the required absolute pressure; do not infer that pressure from an ordinary coarse compound gauge. For example, if the applicable target is $10$ in. Hg vacuum, the gauge must reach at least that level before the appliance is opened. A reading of $8$ in. Hg vacuum does not meet a $10$-in. target.

Verify that the applicable evacuation level has been reached in the appliance or part before opening it. Follow the recovery-unit manufacturer’s operating instructions and use equipment certified for the intended appliance category.

Checking for pressure rebound

A useful field check is to stop recovery at the target, isolate the appliance as appropriate, and observe the pressure. If pressure rises, refrigerant may still be boiling from trapped liquid or coming out of oil. Continue recovery and recheck.

This pressure-rebound check can help reveal residual refrigerant, but it does not replace using the correct instrument or meeting the required endpoint. Waiting after reaching recovery vacuum to check for a pressure rise is identified as a recovery technique.

Verifying recovery cylinders

The appliance evacuation table does not set a vacuum endpoint for an ordinary recovery cylinder. Check that the cylinder is an appropriate, approved recovery cylinder for the refrigerant and pressure involved, is in acceptable condition, and meets applicable inspection or service requirements. Identify its contents and check the cylinder label and manufacturer’s limits.

Prevent overfilling by weighing the cylinder on a suitable scale and accounting for its tare weight. Follow the cylinder’s allowable refrigerant charge and the recovery equipment’s overfill-protection instructions; do not rely on pressure alone to estimate how full the cylinder is.

Equipment test procedures use an $80\%$-by-volume fill condition, but applicable cylinder, refrigerant, transport, and equipment requirements govern actual field handling. For motor-vehicle A/C recovery cylinders, there is a specific $60\%$-of-gross-weighted-capacity limit when the tank lacks a float valve. This is a context-specific rule, not a universal fill limit for every recovery cylinder.