❄️ Stuff Every HVAC Tech Should Know: Training Guide

The ozone shield and chlorine damage

Most of the atmosphere's ozone sits in the stratosphere, a layer about 15 to 30 km above the ground. That layer soaks up much of the sun's harmful ultraviolet light before it reaches us.

A single chlorine atom can destroy over 100,000 ozone molecules before it leaves the stratosphere, because chlorine is not used up in the reaction. Leaked CFC or HCFC refrigerant can therefore do long-lasting damage.

Ozone depletion potential, or ODP, compares a chemical to CFC-11, which is defined as 1.0. A bigger ODP means more ozone damage, and zero means none.

HFC refrigerants have an ODP of zero because they do not contain chlorine. But some HFCs are strong greenhouse gases, which is a separate climate problem.

Refrigerant families and climate impact

EPA's test topics name R-12 as a CFC, R-22 as an HCFC, and R-134 as an HFC. CFCs and HCFCs contain chlorine, so they can deplete ozone. HFCs do not.

Global warming potential, or GWP, compares a gas to carbon dioxide, which has a GWP of 1. A refrigerant with a GWP of 700 traps heat 700 times as strongly per kilogram as carbon dioxide.

R-32 and R-454B are classed A2L, which means they are mildly flammable. They need extra care around ignition sources.

There are no true drop-in replacement refrigerants. Blend refrigerants also undergo fractionation, meaning the blend's components leak at different rates, so the remaining charge may no longer have the original mix.

The basic compression refrigeration loop

The compressor takes in low-pressure refrigerant vapor and squeezes it to a high pressure and high temperature, which requires work input.

In an air-cooled system, the condenser gives up heat to the outdoor air. There the hot refrigerant vapor changes from superheated vapor to sub-cooled liquid.

The evaporator is where low-pressure refrigerant boils and absorbs heat from the air or space being cooled. This is the actual cooling step.

The expansion valve drops the refrigerant's pressure before it enters the evaporator. Some liquid flashes to vapor, so the refrigerant leaves the valve as a mix of liquid and vapor.

Pressure measurements and special refrigerants

A gauge reads pressure above atmospheric pressure. To convert a psig reading to absolute psia, add about 14.7 psi, which is standard atmospheric pressure at sea level.

Standard atmospheric pressure is 29.9 inches of mercury. Absolute pressure counts from a perfect vacuum, so it is the value to use with temperature-pressure charts.

Mildly flammable A2L refrigerants such as R-32 and R-454B must be handled carefully. Technicians must keep potential ignition sources away during service.

International and US phaseout milestones

Countries signed the Montreal Protocol in 1987 as the first step in international efforts to protect stratospheric ozone.

The Kigali Amendment to the Montreal Protocol extended controls to phase down HFCs, which do not harm ozone but can warm the climate.

In the US, the ban on producing and importing CFCs took effect on January 1, 1996. Halon production and import had already been banned on January 1, 1994.

Since 2020 there has been no new production or import of R-22 in the US. All HCFCs end in 2030.

The AIM Act requires US HFC production and use to fall by 85 percent from baseline by 2036. EPA started the phasedown with a 10 percent reduction in 2022 and dropped to 60 percent of baseline in 2024.

Section 608 and the venting prohibition

Section 608 of the Clean Air Act created the National Recycling and Emission Reduction Program. It is why technicians need certification, must recover refrigerant, and cannot vent it.

The venting ban in Section 608 covers both ozone-depleting refrigerants and their substitutes, including HFCs. Any work that maintains, services, repairs or disposes of equipment must recover the refrigerant instead of releasing it.

Installing an R-410A mini-split, even just connecting pre-charged lines, requires Section 608 certification.

The venting rule lists a few exempt substitutes, including carbon dioxide, nitrogen and water in any application. Refrigerants like R-134a and R-22 are not exempt.

Once refrigerant has been recovered, knowingly releasing it is a violation of the venting prohibition. Small accidental losses during a good-faith recovery can be de minimis, but only when the technician follows required recovery practices.

Certification and personnel

Certification types match appliance categories: Type I for small appliances, Type II for medium, high and very high-pressure equipment, Type III for low-pressure equipment. A technician who works on all categories needs Universal. EPA does not offer a separate R-410A certification; certification is by appliance type, not refrigerant.

An apprentice can work on refrigerant circuits without their own certification for up to two years after first registering. During that time, a certified technician with the correct certification must closely and continually supervise the apprentice.

Certification cards come from the EPA-approved organization that tested and certified you, not from EPA. If you lose the card, contact that organization for a replacement.

Under EPA's sales restriction, a seller may legally sell refrigerant for use in equipment only to a certified technician, or to a buyer who employs one and can show proof.

Recovery and recycling machines must be certified through an EPA-approved third-party testing organization. They must also have low-loss fittings on all hoses.

Documentation basics

Technicians must keep records of refrigerant recovered from disposed appliances holding 5 to 50 pounds for three years. An employer can keep them for its technicians.

On appliances that normally hold 50 or more pounds of ozone-depleting refrigerant, the technician must give the customer an invoice showing the amount of refrigerant added.

A standing pressure decay test alone shows that leaking is happening, but it does not show where the leak is. It must be paired with a method that locates the leak, such as an ultrasonic test, gas-imaging camera or bubble test.

Connecting or disconnecting hoses and gauges to read pressures is not considered opening an appliance, but it still requires Section 608 certification.

The Three Rs

To recover means to remove refrigerant in any condition and store it in an external container, with no testing or processing.

To recycle means to extract refrigerant and clean it for reuse in equipment owned by the same owner, usually by oil separation and filter-driers.

To reclaim means to reprocess recovered refrigerant to new-product purity specifications, verified by analysis. Only then can it be sold.

Technicians need to avoid mixing different refrigerants together. A mixed batch may not be reclaimable because each refrigerant must meet its own purity specs.

Cylinders and pressure safety

A refrigerant cylinder should be filled to no more than 80 percent by volume. The empty 20 percent is called head pressure room, and it gives the liquid room to expand when it warms.

Reusable recovery cylinders must be DOT approved and use the yellow and gray color code. Disposable cylinders must never be refilled.

DOT rules for liquefied gas cylinders say the liquid portion must never completely fill the cylinder at temperatures up to 131 F. A liquid-full cylinder has no room for expansion and can burst.

For leak testing, use dry nitrogen rather than oxygen or compressed air. Nitrogen is the best leak test gas for EPA's Type 2 outline.

When pressurizing a system with nitrogen, use a pressure regulator and a relief valve. The regulator sets a safe test pressure, and the relief valve lets gas out if pressure climbs too high.

Evacuation and moisture control

A vacuum pump removes air and moisture from a system at the end of service before it is charged.

Polyolester oil, or POE oil, absorbs moisture very quickly. Keep line set caps on until you connect them, because leaving lines open means extra evacuation to remove moisture.

Keep the refrigerant system closed as much as possible when working with HFC systems and POE oil.

On an HFC system with POE oil, leaving the refrigerant lines open means you will need extra evacuation to remove the moisture the oil absorbs.

Exposure and A2L safety

Refrigerant exposure can cause oxygen deprivation, cardiac effects, frostbite and long-term hazards. Equipment room requirements include an oxygen deprivation sensor with all refrigerants.

A halide torch or any other leak detector using a naked flame must never be used on a system with a mildly flammable A2L refrigerant. Use bubble solutions or suitable electronic detectors.

If a leak is suspected on an A2L system, all naked flames must be removed or extinguished.

Under EPA's 2024 rule, a 608-certified tech may evacuate a disposable cylinder to 15 inches of mercury before disposal instead of refilling it.

Small appliance definition and access

EPA defines a small appliance as a factory-sealed unit with five pounds or less of refrigerant. Examples include home refrigerators, window air conditioners, vending machines, dehumidifiers, under-the-counter ice makers and drinking water coolers.

A factory-sealed window air conditioner counts as a small appliance under EPA's definition.

A process stub is a short resealable tube on a small appliance or room air conditioner that gives a technician access to the refrigerant.

A person who only disposes of small appliances does not need Section 608 certification. But servicing or repairing a small appliance, such as attaching gauges, does require Type I or higher certification.

Recovery targets

Using recovery equipment made on or after November 15, 1993, recover 90 percent when the small appliance's compressor is running.

If the compressor is not working, the target drops to 80 percent with post-1993 recovery equipment.

Instead of recovering a percentage, a technician can evacuate a small appliance to four inches of mercury vacuum.

Using recovery equipment made before November 15, 1993, recover 80 percent of the refrigerant, whether the compressor is working or not.

The small appliance recovery rules apply both before opening a small appliance and when disposing of one.

Techniques and tools

System-dependent recovery equipment, also called passive equipment, needs components in the appliance to help remove the refrigerant. Self-contained equipment has its own means, so it works without the appliance's help.

When recovering from a small appliance with an inoperative compressor, install both high-side and low-side access valves. Run a working compressor when using a passive system-dependent recovery device.

Remove solderless access fittings after finishing a small appliance service. They are temporary tools for getting to the refrigerant.

Small-appliance recovery equipment itself must be certified to recover 90 percent with the test stand compressor running and 80 percent with it off.

Mail-in Type I tests have a passing score of 84 percent, and they cannot count toward a Universal certification. Training material sent with mail-in Type I tests may not include sample questions that mimic the real test.

Pressure classes and recovery levels

EPA calls a refrigerant high-pressure if its liquid saturation pressure at 104 F falls between 170 and 355 psia. Very high-pressure is above 355 psia, or a critical temperature below 104 F. Medium-pressure is 45 to 170 psia, and low-pressure is below 45 psia.

R-410A, R-22, R-407A, R-407C and R-502 are examples of high-pressure refrigerants. R-134a belongs to the medium-pressure class, and R-11 and R-123 are low-pressure refrigerants.

For a medium-pressure appliance under 200 pounds, post-1993 recovery equipment must evacuate to 10 inches of mercury vacuum.

For a high-pressure appliance under 200 pounds, post-1993 recovery equipment must evacuate to 0 inches of mercury vacuum, which is atmospheric pressure.

A high-pressure appliance with 200 pounds or more must reach 10 inches of mercury vacuum with post-1993 equipment.

For a non-major repair where the appliance will not be evacuated to the atmosphere afterward, evacuate to no higher than 0 psig before opening.

Major repairs and safe opening

EPA says a repair is major if it involves removing the compressor, condenser, evaporator or auxiliary heat exchange coil. Major repairs require evacuating to the Table 1 levels.

A repair that uncovers an opening of more than four square inches of flow area for more than 15 minutes is also major.

After reaching the required recovery vacuum, wait a few minutes to see if system pressure rises. A rise means there is still liquid refrigerant in the system or in the oil.

Never energize a hermetic compressor while it is under a vacuum. Powering one up while the system is evacuated is unsafe.

System-dependent recovery equipment may not be used on appliances holding more than 15 pounds of refrigerant, unless it is a pump-out unit permanently attached to the appliance.

Leak repair rules for large appliances

Section 608 leak repair rules apply to appliances with a full charge of at least 50 pounds of an ozone-depleting refrigerant. Since April 10, 2020, they do not apply to appliances containing only substitute refrigerants such as HFCs.

EPA's 2024 HFC leak repair rule applies to appliances holding at least 15 pounds of an HFC or substitute with a GWP above 53. Residential and light commercial AC and heat pumps are excluded.

Commercial refrigeration, such as supermarket and cold storage systems, triggers repair at a leak rate over 20 percent per year. Industrial process refrigeration triggers at 30 percent, and comfort cooling triggers at 10 percent.

Owners must identify and repair leaks within 30 days. If the repair needs an industrial process shutdown, the period is 120 days. Parts availability extensions are capped at 180 days, or 270 days with an industrial process shutdown.

A follow-up verification test must be done within 10 days of the successful initial test. Both tests must show the repair worked.

Commercial and industrial process systems with a full charge of 500 pounds or more need leak inspections every three months. These quarterly inspections continue until leak rate calculations show no excess for four quarters in a row. Commercial and industrial systems of 50 to 499 pounds, and comfort cooling, need yearly inspections, and those continue until a full year passes below the leak-rate threshold.

Plans, reports and definitions

An owner who chooses to retire or retrofit a leaking appliance must create a plan within 30 days and finish the work within one year of the plan's date. The plan must be signed and kept at the site.

Owners of appliances holding 50 or more pounds that leak 125 percent or more of their charge in a calendar year must send EPA a report by March 1 of the following year.

EPA defines leak rate as the percent of the full charge that would be lost over 12 months if the current rate of loss continued. Facilities can use the annualizing method or the rolling average method, but must use the same one for all appliances.

To mothball an appliance means to evacuate it to at least atmospheric pressure and temporarily shut it down. The leak repair clock pauses while it is mothballed and restarts when refrigerant is added again.

Connecting and disconnecting hoses and gauges to read pressure is not considered opening an appliance.

Low-pressure chillers

A low-pressure refrigerant has a liquid saturation pressure below 45 psia at 104 F. Examples include R-11, R-123, R-113 and R-245fa.

Low-pressure appliances must be evacuated to 25 mm Hg absolute pressure. This level is the same whether the recovery equipment was made before or after November 15, 1993.

For a non-major repair on a low-pressure appliance that will not be evacuated to the atmosphere afterward, pressurize to no higher than 0 psig before opening.

If the refrigerant boils at or below 85 F at standard atmospheric pressure, do not use nitrogen that requires purging afterward. Use controlled hot water or a built-in heating device.

Heat the chiller oil to 130 F before removing it. The goal is to minimize refrigerant release when the oil comes out.

During refrigerant evacuation of a chiller, circulate or remove the water to prevent the water from freezing.

When recharging a low-pressure chiller, introduce vapor before liquid to prevent freezing of water in the tubes.

Excessive purging on a low-pressure chiller is a sign of leakage into the system. Under ASHRAE Standard 15, R-123 equipment rooms need a refrigerant sensor.

Sales and reclamation

It is the wholesaler's responsibility to determine whether a person claiming to represent a buyer really is an authorized representative. An employer can buy refrigerant by giving the wholesaler written evidence that it employs at least one certified technician.

Small cans of car air conditioner refrigerant, like R-134a, may be sold to uncertified buyers if the cans hold at most 2 pounds. They must have unique fittings and self-sealing valves.

Refrigerant sellers must keep invoices showing the purchaser's name, the date of sale and the quantity for three years.

Someone with only a Section 609 car air conditioning certification cannot buy refrigerant for stationary equipment. Only Section 608 certified technicians can buy stationary refrigerants, regardless of container size.

Used refrigerant normally must be reclaimed before it is sold. One exception is a transfer between a parent company and its subsidiary, or between subsidiaries of the same parent.

Certification tests and recordkeeping

Section 608 technician certification does not expire. Certifying programs must issue a wallet-sized identification card within 30 days of the test.

For Universal certification, the core test must be taken as a proctored exam, not open book. Mail-in Type I tests cannot count toward a Universal certification.

Closed-book Type I, II, III and Universal tests use a 70 percent passing score. Only mail-in Type I tests require a higher 84 percent.

A Universal test has 100 questions. It is 25 core questions plus 25 from each of the Type I, II and III areas.

An uncertified apprentice may work on refrigerant circuits only if a certified technician closely and continually supervises them. The apprentice must be registered with the U.S. Department of Labor's Office of Apprenticeship or a recognized State Apprenticeship Council.

A scrap yard can rely on a signed statement that a junked fridge's refrigerant was recovered. The statement must include the name and address of the person who recovered the refrigerant and the date of recovery.

Technology transitions

New VRF systems must have a GWP of 700 or less. If a higher-GWP system has all components manufactured or imported before January 1, 2026, it can be installed up to January 1, 2027.

A further extension to January 1, 2028 applies to buildings with a permit approved before October 5, 2023 that specified an HFC system.