4 Type III: Low-Pressure Appliances

Scope and operating conditions

Type III certification covers servicing and disposing of low-pressure appliances, particularly centrifugal chillers. Common refrigerants in these appliances include R-11 and R-123. Technicians must use practices appropriate to the appliance and must not intentionally vent refrigerant.

Pressure, purging, and leak clues

Parts of a low-pressure refrigeration circuit can operate below atmospheric pressure. Air and moisture may therefore leak inward, while refrigerant may leak outward. A chiller operating below atmospheric pressure does not necessarily mean refrigerant is leaking outward at that moment.

Low-pressure refrigerants boil at low temperatures when their absolute pressure is low. Distinguish psig, which is pressure relative to atmosphere, from psia, which is absolute pressure; temperature-pressure charts generally use absolute pressure.

A purge unit removes air and other noncondensables that enter the system. Frequent or excessive purging is a warning sign of air ingress and may indicate a leak. Air and moisture reduce performance and can contribute to corrosion and other damage.

Leak testing and repair obligations

The preferred leak-test pressurization methods are controlled heating, such as hot water or a built-in heating or pressurization device, followed, if needed, by nitrogen. Do not exceed the appliance’s specified limits. For certification review, the maximum leak-test pressure for a low-pressure centrifugal chiller is $10$ psig. Never use oxygen or compressed air to pressurize a refrigeration system.

A leak test should help locate the leak, not merely show that pressure changes. Excessive purging is a clue, but it does not replace finding and repairing the leak.

Leak-repair requirements

For an appliance subject to EPA leak-repair requirements, determine its refrigerant type, full charge, use, and applicable rules. EPA’s current Section 608 guidance lists leak-repair trigger rates for covered appliances containing at least $50$ pounds of ozone-depleting refrigerant:

• Industrial process refrigeration: $30\%$.

• Commercial refrigeration: $20\%$.

• Comfort cooling and other appliances: $10\%$.

A comfort-cooling chiller is included in the comfort-cooling category. Owners generally must repair qualifying leaks within $30$ days or develop a retrofit or retirement plan within that period. Verification, recordkeeping, and reporting requirements may also apply. Applicability can differ by refrigerant and other rules, so verify current requirements rather than assuming the same threshold applies to every chiller.

Recovery and evacuation

Before opening an appliance for service or disposal, recover refrigerant with appropriate certified equipment and follow the manufacturer’s instructions. The required evacuation level for low-pressure appliances is $25$ mm Hg absolute, approximately $1$ in. Hg absolute, regardless of whether the recovery equipment was manufactured before or after November 15, 1993. This is an absolute pressure, not $25$ mm Hg of vacuum on a compound gauge.

Recover liquid refrigerant early when possible, because removing liquid first generally speeds recovery. Recover vapor as well as liquid. After reaching the required level, wait several minutes and check for a pressure rise. A rebound can indicate refrigerant still boiling from liquid or escaping from oil; continue recovery as appropriate rather than treating the first reading as proof that recovery is complete.

During evacuation, circulate or remove water from the chiller tubes to prevent freezing. Low-pressure recovery equipment uses a high-pressure cut-out; the Type III review value is $10$ psig. Follow the equipment manufacturer’s directions and appliance-specific procedures.

Before removing oil, heat it to approximately $130^\circ\text{F}$ to reduce refrigerant remaining in solution. EPA also requires reducing appliance or isolated-section pressure to $5$ psig or less before an oil change, or draining the oil into a receiver that will be brought to that pressure.

Repair procedures and exceptions

In general, evacuate the appliance or isolated section to the required level before opening it for a major repair. If a leak prevents the required evacuation, isolate leaking from non-leaking sections where possible. Evacuate sound sections to the required level and the leaking section to the lowest achievable pressure, no higher than $0$ psig.

A limited exception applies when a repair is not major and the appliance will not be evacuated to the atmosphere after the repair: pressurize the low-pressure appliance to $0$ psig before opening it. Use heat or a built-in pressurization device as appropriate. For refrigerants with boiling points at or below $85^\circ\text{F}$ at standard atmospheric pressure, do not use nitrogen or another method that would require subsequent purging; R-113 is a stated exception. This exception does not permit venting refrigerant.

Recharging and equipment-room safety

When recharging a chiller, introduce refrigerant vapor before liquid to reduce the risk of freezing water in the tubes. Charge a centrifugal chiller through the evaporator charging valve.

Low-pressure equipment rooms require attention to oxygen-displacement hazards because a refrigerant release can displace breathable air. Type III exam topics identify oxygen-deprivation sensing and an equipment-room refrigerant sensor for R-123 as safety subjects. Follow applicable mechanical-code requirements, site procedures, and manufacturer instructions; use appropriate ventilation and personal protective equipment. Never enter a potentially oxygen-deficient space without proper safeguards.

Recovered refrigerant may generally be returned to the same appliance or another appliance owned by the same person. If ownership changes, the refrigerant must be reclaimed by an EPA-certified reclaimer before resale or reuse by the new owner.

• Leak-repair trigger rate

• Refrigerant reclamation