9.2 Type II Recovery Methods and Required Evacuation Levels

Recovery Methods for High-Pressure Systems

Recovery is the removal of refrigerant from an appliance and its storage in an external cylinder — it must be done before any system is opened for major service or disposed of. Type II systems range from a 4-lb mini-split to a 1,000-lb industrial rack, so technicians use whichever recovery method (or combination) moves the charge fastest and safest.

The Three Recovery Approaches

1. Vapor recovery. The recovery machine draws refrigerant vapor from the appliance's low (suction) side, compresses it, condenses it, and pushes it into the cylinder. Vapor recovery is gentle and universal but slow, because vapor is far less dense than liquid. It is the method used to finish a recovery and to pull the system down into a vacuum.
2. Liquid recovery. The machine pulls liquid refrigerant directly from the system's liquid line or receiver and routes it to the cylinder. Because liquid is dense, this method removes the bulk of the charge very quickly. Most field recoveries start with liquid to clear the majority of the charge, then switch to vapor to capture what remains.
3. Push-pull recovery. Reserved for large charges (typically over ~10-15 lbs of liquid), push-pull is the fastest method. The recovery machine "pulls" vapor from the top of the recovery cylinder, lowering pressure there, while it "pushes" by raising pressure in the appliance — the resulting pressure difference forces liquid from the system into the cylinder in a continuous stream. Push-pull cannot be used on small appliances or any system where you cannot establish a clear liquid path.

Push-Pull, Step by Step

1. Connect the recovery machine inlet to the vapor port of the recovery cylinder.
2. Connect the recovery machine outlet back to the appliance's vapor (suction) side.
3. Connect the appliance's liquid line to the liquid port of the recovery cylinder.
4. Start the machine; it lowers cylinder pressure and raises system pressure, driving liquid from the system into the cylinder.
5. Watch the cylinder scale — stop at 80% of cylinder capacity — and switch to vapor recovery to remove the remaining vapor charge and pull the required vacuum.

Safety: A recovery cylinder must never be filled beyond 80% of its rated capacity. Liquid refrigerant expands as it warms; an overfilled cylinder can become hydrostatically full and rupture. Use a cylinder scale or a float/level shutoff, and weigh the cylinder rather than guessing.

Self-Contained vs. System-Dependent Recovery Equipment

For Type II work, you will almost always use self-contained recovery equipment, because virtually every Type II appliance holds more than 5 lbs. System-dependent equipment is a Type I tool. Recovery equipment manufactured on or after November 15, 1993 must be certified by an EPA-approved laboratory to meet the required recovery and evacuation standards.

Required Evacuation Levels (Memorize This Table)

Before an appliance is opened for service or final disposal, refrigerant must be recovered down to a required evacuation level measured in inches of mercury (Hg) vacuum. EPA sets the required level by appliance pressure category, charge size, and the manufacture date of the recovery equipment. This is one of the most heavily tested topics on the Type II exam.

(For reference, low-pressure Type III appliances require 25 mm Hg absolute — roughly 29 inches Hg vacuum — but that is a Type III value.)

Reading the Table Correctly

A few patterns make this table easier to remember:

• Very high-pressure and small high-pressure systems (under 200 lbs) require only 0 inches Hg — that is, recover down to atmospheric pressure (0 psig). You do not need to pull a vacuum.
• The deepest required vacuum (15 inches Hg) applies to large MEDIUM-pressure systems, not high-pressure ones. A common exam trap is to assume a big high-pressure system needs 15 inches — it needs 10 inches Hg (post-1993 equipment).
• The required level is measured at the system service valves at the end of recovery, after the recovery machine has stopped and the system has stabilized.

Worked Example: You are recovering refrigerant from a 350-lb R-22 high-pressure chiller using a recovery machine manufactured in 2021. What is your required evacuation level? R-22 is high-pressure; the charge is 200 lbs or more; the equipment is on or after Nov 15, 1993. Reading the table: the required level is 10 inches Hg vacuum. If the same job used a recovery machine built in 1991, the requirement would drop to 4 inches Hg vacuum. Had this been a 350-lb R-134a (medium-pressure) system with the 2021 machine, the requirement would rise to 15 inches Hg vacuum.

Verifying the Final Vacuum

After you reach the required level, isolate the system by closing the recovery valves and watch the gauges. A pressure rise indicates either trapped refrigerant boiling off (recover further) or a leak (locate and repair before recharging). Only when the reading holds at or below the required level is recovery legally complete.