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newSchoolWorks.com › VoTechWorks › Building & Construction › HVAC/R › Heat Pumps: Principles, Installation, and Service › Lesson 5
BLD-HVAC07-04 · Lesson 5 · 18 clock hours · lab

Refrigerant Recovery, Evacuation, and Recharge: Heat Pump Procedures

Objective. The student will recover, evacuate to 500 microns or less, and recharge a heat pump trainer unit with the correct refrigerant type and factory charge weight using a recovery machine, manifold gauge set, micron gauge, and refrigerant scale.

Why Refrigerant Handling Procedures Matter

Every time a heat pump system is opened for service, three tasks must be completed in the correct order: recovery, evacuation, and recharge. Skipping or rushing any step can leave moisture and non-condensables in the system, release refrigerant to the atmosphere in violation of federal law, or result in an incorrect charge that shortens equipment life. Section 608 of the Clean Air Act prohibits the intentional venting of refrigerants, and only EPA 608-certified technicians may purchase and handle refrigerants covered by that rule.

Recovery: Removing the Refrigerant Safely

Refrigerant recovery means transferring the system charge into an approved recovery cylinder before opening any refrigerant circuit. Use a UL-listed recovery machine rated for the refrigerant in the trainer (R-410A or R-32). Both refrigerants operate at higher pressures than older R-22 systems, so your manifold gauge set, hoses, and recovery machine must all be rated for R-410A service pressures.

Cylinder safety: Recovery cylinders must not be filled beyond 80% of their water capacity to allow for liquid expansion. Before connecting the cylinder, check its tare weight label, confirm it is the correct cylinder type for the refrigerant, and verify it is within its retest date. Never use a disposable refrigerant cylinder as a recovery vessel.

Connect the recovery machine per the manufacturer's procedure—typically low-side and high-side hoses from the manifold to the system service ports, and a third hose from the manifold center port to the recovery cylinder inlet. Run the machine until the system pressure reaches the low-pressure cutout specified by the recovery machine manufacturer. Log the starting and ending cylinder weight.

Evacuation: Pulling a Deep Vacuum

Once recovery is complete, the system must be evacuated to remove moisture and air. Moisture combines with refrigerant oil to form acids that destroy compressors. Air is a non-condensable that raises head pressure and reduces efficiency.

Disconnect the recovery machine and connect a micron gauge directly to the system—not through long hose runs, which add volume and slow readings. Use a two-stage vacuum pump rated for the system size. Pull the vacuum down and verify the system reaches 500 microns (0.5 torr) or less. Once you hit that target, close the pump isolation valve and watch the micron gauge for five minutes. If the reading rises above 500 microns and continues climbing, there is a leak or remaining moisture. If it rises slightly and levels off, residual moisture is present and continued evacuation is needed. A stable reading at or below 500 microns means the system is ready.

After a satisfactory vacuum hold, break the vacuum with dry nitrogen pushed in through a regulator to a low positive pressure (commonly around 1–2 psig above atmospheric, per your procedure). This prepares the system for a standing leak check before recharge. Never break a vacuum with refrigerant—this can cause a flammable mixture if R-32 is involved and is poor practice with any refrigerant.

Recharge: Weighing In the Correct Charge

The factory nameplate or service literature specifies the exact refrigerant type and charge weight for the unit. Obtain this value before opening any refrigerant container. Charging by weight is the most accurate method for a system that has been fully recovered and evacuated.

Place the refrigerant cylinder on a digital refrigerant scale and zero (tare) the scale with the cylinder and hose connected. Charge liquid refrigerant into the high side of the system with the system off, or follow the trainer manufacturer's procedure if liquid charging through the low side with the cylinder inverted. Watch the scale reading and stop when you have added the target weight.

Verify the charge using the manufacturer's specified method:

Record all gauge pressures, temperatures, scale weights, and micron readings on the lab log sheet.

Personal Protective Equipment and Safety Rules

Key terms9

RecoveryThe process of removing refrigerant from a system and storing it in an approved recovery cylinder without releasing it to the atmosphere, as required by EPA Section 608.
EvacuationUsing a vacuum pump to remove air and moisture from a refrigerant system before recharging; the system must reach 500 microns or less and hold that level to be considered clean and dry.
Micron gauge (electronic vacuum gauge)An instrument that measures system vacuum in microns of mercury (µmHg); used to confirm the system has reached and is holding the required deep vacuum level.
SubcoolingThe number of degrees by which liquid refrigerant in the liquid line has been cooled below its saturation temperature at the measured condensing pressure; used to verify correct charge in TXV/EEV systems.
SuperheatThe number of degrees by which refrigerant vapor in the suction line exceeds its saturation temperature at the measured suction pressure; used to verify correct charge in fixed-orifice systems.
Non-condensablesGases such as air or nitrogen that do not condense at normal operating pressures; they raise head pressure, reduce efficiency, and must be removed by evacuation.
Recovery cylinderA DOT-approved, color-coded cylinder designed to receive and store recovered refrigerant; must not be filled beyond 80% of water capacity.
Tare weightThe known empty weight of a cylinder or container; zeroing a scale with the empty cylinder and hose allows accurate measurement of only the refrigerant added or removed.
A2L refrigerantAn ASHRAE refrigerant safety classification indicating lower toxicity (A) and mild flammability (2L, with a low burning velocity); R-32 falls in this class and requires attention to ignition sources.

Worked examples4

1. The trainer nameplate calls for 3 lb 4 oz of R-410A. You tare the scale with the cylinder and hose connected. How many ounces of refrigerant must the scale show removed from the cylinder when charging is complete?
  1. Convert the target charge to ounces: 3 lb × 16 oz/lb = 48 oz, plus 4 oz = 52 oz total.
  2. Because the scale was tared (zeroed) with the full cylinder in place, the scale will show a negative reading as refrigerant leaves the cylinder.
  3. Stop charging when the scale reads −52 oz (52 oz removed from the cylinder).
Answer: 52 oz must be removed from the cylinder; stop when the scale reads −52 oz.
2. After pulling a vacuum you close the pump isolation valve. The micron gauge reads 380 microns at the moment of closure. Five minutes later it reads 480 microns and appears to have leveled off. Does the system pass the vacuum hold test?
  1. The pass criterion is: the reading must be at or below 500 microns AND must hold (not continue rising) for five minutes.
  2. Final reading is 480 microns, which is below 500 microns.
  3. The reading rose from 380 to 480 and then leveled off—this indicates residual moisture outgassing, not an active leak, but the reading is still within the 500-micron limit.
  4. Evaluate: 480 microns ≤ 500 microns and the rise has stabilized, so the system meets the stated 500-micron hold criterion.
Answer: Yes, the system passes: 480 microns is at or below 500 microns and the reading stabilized, meeting the five-minute hold requirement.
3. A heat pump with a TXV is operating in cooling mode. The high-side gauge reads 390 psig on R-410A. The saturation temperature at that pressure (from an R-410A pressure-temperature chart) is 105 °F. The liquid-line temperature measured with a clamp probe is 90 °F. What is the subcooling, and is it within a typical nameplate target of 10–15 °F?
  1. Subcooling = Saturated condensing temperature − Actual liquid-line temperature.
  2. Subcooling = 105 °F − 90 °F = 15 °F.
  3. Compare to the target range of 10–15 °F: 15 °F is at the upper edge of the range.
Answer: Subcooling is 15 °F, which is at the top of the 10–15 °F target range and acceptable; no adjustment is needed unless the nameplate specifies a tighter tolerance.
4. A recovery cylinder has a water capacity of 50 lb. What is the maximum weight of refrigerant that may be stored in it?
  1. The 80% rule: maximum fill = 0.80 × water capacity.
  2. Maximum fill = 0.80 × 50 lb = 40 lb.
  3. Stop recovery before the cylinder contains more than 40 lb of refrigerant.
Answer: The maximum refrigerant that may be stored is 40 lb (80% of 50 lb water capacity).

The math in this lesson2

Learners compute 80% of a recovery cylinder's 50 lb water capacity and read a vacuum rise rate.
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Brush up in the math halls at newSchoolWorks.com:
In class: Set up the recovery machine on the heat pump trainer following the equipment manufacturer's procedure; recover the refrigerant charge into an approved recovery cylinder, verifying the cylinder is not filled beyond 80% capacity. · Connect micron gauge to the system after recovery; pull a deep vacuum and verify the system holds at or below 500 microns for five minutes before breaking the vacuum with dry nitrogen for a leak check. · Weigh in the factory-specified refrigerant charge using a digital refrigerant scale; verify charge using manufacturer superheat or subcooling method; record all readings on the lab log sheet.
Materials: Heat pump trainer unit, recovery machine (UL-listed), manifold gauge set (rated for R-410A), micron gauge, digital refrigerant scale, recovery cylinder, dry nitrogen tank with regulator, refrigerant (R-410A or R-32 per trainer), safety glasses, gloves, face shield, EPA 608 prep reference, lab log sheets
Check: Instructor verifies micron gauge reading at or below 500 microns and holds for five minutes; final refrigerant weight within ±2 oz of target; all PPE worn throughout; lab log complete; pass mark: all three criteria met.

Practice check8

Answer each question, then check it. Nothing is recorded; this is your own practice.

EPA 608 – Regulatory requirements and refrigerant handling
1. Under EPA Section 608, what is a technician required to do before opening a refrigerant circuit for service?
EPA 608 – Recovery equipment and cylinders
2. What is the maximum allowable fill level for a refrigerant recovery cylinder?
NATE – System evacuation and moisture removal
3. A technician pulls a vacuum and then closes the vacuum pump isolation valve. The micron gauge reads 620 microns after five minutes. What does this most likely indicate?
HVAC Excellence – Tools and instrumentation
4. Which instrument is used to verify that a system has reached and is holding the required deep vacuum?
NCCER HVAC – Service procedures
5. After a satisfactory vacuum hold test, the recommended way to break the vacuum before a leak check is to introduce:
NATE – Heat pump charging and system performance
6. Which charging verification method is most appropriate for a heat pump equipped with a thermostatic expansion valve (TXV)?
EPA 608 – Refrigerant safety classifications
7. R-32 carries an ASHRAE A2L safety classification. What does the '2L' indicate, and what precaution does it require in the lab?
NCCER HVAC – Refrigerant charging by weight
8. When charging by weight, a technician tares the scale with the refrigerant cylinder and hose connected. The nameplate charge is 2 lb 8 oz. At what scale reading should the technician stop charging?
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