8 Type III: Low-Pressure Appliances

Type III scope and low-pressure appliances

Type III certification covers the servicing, repairing, and disposal of low-pressure appliances, commonly centrifugal chillers. A low-pressure appliance uses a refrigerant whose liquid-phase saturation pressure is below $45\ \text{psia}$ at $104^\circ\text{F}$. Common refrigerants include R-11, R-123, R-113, and R-245fa.

Low-pressure chillers may operate below atmospheric pressure. A leak in a section under vacuum can draw air and moisture into the system. During service, use recovery equipment certified for the refrigerant and appliance type, follow the equipment manufacturer’s instructions, and do not knowingly vent regulated refrigerants.

Recovery and evacuation

The required recovery endpoint for a low-pressure appliance is $25\ \text{mm Hg}$ absolute. This is an absolute pressure, not $25\ \text{mm Hg}$ of vacuum. The endpoint does not change with the appliance’s charge size or the recovery equipment’s manufacture date. A technician may evacuate the entire appliance or an isolated portion that can be contained in a system receiver. Verify that the required level has been reached before opening the appliance.

A practical sequence is to recover liquid first to speed removal, then recover the remaining vapor. Removing visible or accessible liquid does not mean the appliance is empty. During evacuation, circulate or remove water in the chiller as appropriate to reduce the risk of freezing and damaging tubes.

After reaching the endpoint, wait a few minutes and check for pressure rebound. A pressure rise may indicate that refrigerant remains in the system or is coming out of oil; continue recovery as needed. Before removing oil, heat it to about $130^\circ\text{F}$ to reduce dissolved refrigerant. Do not change the oil until the appliance or isolated section is at $5\ \text{psig}$ or lower, or until the oil has been drained into a receiver that can be brought to that pressure.

For Type III exam preparation, the traditional recovery-unit high-pressure cutout value when recovering a low-pressure chiller is $10\ \text{psig}$. This is an equipment setting, not the recovery endpoint of $25\ \text{mm Hg}$ absolute. Follow the chiller and recovery-machine manufacturers’ instructions.

Repair requirements and exceptions

A major repair requires the applicable evacuation procedures to be followed before opening the appliance. It includes removing a compressor, condenser, evaporator, or auxiliary heat-exchange coil, as well as opening more than $4\ \text{in}^2$ of flow area and leaving that opening uncovered for more than $15$ minutes.

A limited exception applies to a non-major repair when the appliance will not be evacuated to the atmosphere after the repair. Before opening it, pressurize the low-pressure appliance to no higher than $0\ \text{psig}$, using heat to raise the pressure. Cover openings when isolation is not possible.

The regulation restricts methods such as nitrogen that require later purging. For refrigerants with normal boiling points at or below $85^\circ\text{F}$, do not use such methods. For refrigerants with higher boiling points, use heat as much as possible; nitrogen may be used to raise pressure from the level achieved with heat to atmospheric pressure.

If a leak prevents the required evacuation, isolate leaking components from non-leaking components where possible. Evacuate the non-leaking components to the required level, and recover from the leaking components to the lowest attainable pressure, no higher than $0\ \text{psig}$.

Purge units and leak detection

A purge unit removes air and other noncondensable gases that accumulate in low-pressure systems. It separates and returns refrigerant from the purge stream while discharging noncondensables. Air can enter through leaks in chiller parts operating below atmospheric pressure, and noncondensables can impair heat transfer and raise operating pressure.

Frequent or increasing purge operation is a warning sign of possible leakage, not proof of a specific leak location. Investigate the cause and locate leaks; a purge unit is not a substitute for repair.

Because parts of a low-pressure chiller may be under vacuum, leak detection can require safely raising system pressure. Controlled hot water or a built-in heating and pressurization device is the preferred approach. Nitrogen is another method, subject to the restrictions for non-major repairs. The commonly taught maximum leak-test pressure for a low-pressure centrifugal chiller is $10\ \text{psig}$. Treat this as a ceiling, not a target, and follow the appliance manufacturer’s instructions and pressure limits.

Use an appropriate method to locate leaks, such as an electronic detector or bubble solution where suitable. A pressure or vacuum decay test can indicate that a system is leaking, but does not by itself locate the leak.

Section 608 leak-repair thresholds

Under the Section 608 leak-repair rules, owners or operators must take corrective action when an appliance with a full charge of at least $50$ pounds of ozone-depleting refrigerant exceeds its applicable annual leak-rate threshold. The trigger rates are:

• Industrial process refrigeration: $30\%$.

• Commercial refrigeration: $20\%$.

• Comfort cooling: $10\%$.

• Other appliances: $10\%$.

These are annualized thresholds, and the rules also include repair, verification, and recordkeeping provisions. Appliances containing at least $50$ pounds that leak at least $125\%$ of their full charge in a calendar year are subject to chronic-leak reporting. These Section 608 thresholds concern ozone-depleting refrigerants and should not be assumed to describe requirements under other federal programs.