8 Type III: Low-Pressure Appliances Free Online FlashCards

What pressure criterion defines a low-pressure appliance?

A Type III low-pressure appliance uses a refrigerant whose liquid-phase saturation pressure is below 45 psia at 104°F.

Name two refrigerants commonly used in low-pressure appliances.

Common examples include R-11, R-123, R-113, and R-245fa.

What is the required evacuation endpoint for a low-pressure appliance?

The required evacuation endpoint is 25 mm Hg absolute, regardless of charge size or recovery equipment manufacture date.

In what order should refrigerant phases be recovered?

Recover accessible liquid first to speed removal, then recover the remaining vapor.

Why manage water in a chiller during evacuation?

Circulate or remove the water as appropriate to reduce the risk of freezing and damaging chiller tubes.

What should a technician do after reaching the evacuation endpoint?

Wait a few minutes and check for pressure rebound. A rise can indicate refrigerant remains or is emerging from oil, so continue recovery as needed.

What is the traditional recovery-unit high-pressure cutout value?

The traditional Type III exam value for the recovery unit’s high-pressure cutout is 10 psig. This is an equipment setting, not the evacuation endpoint.

What qualifies as a major repair on a low-pressure appliance?

A major repair involves removing a compressor, condenser, evaporator, or auxiliary heat-exchange coil, or leaving an opening over 4 square inches uncovered for more than 15 minutes.

What pressure applies to the non-major repair exception?

For a qualifying non-major repair that will not be followed by evacuation to the atmosphere, pressurize the appliance to no higher than 0 psig before opening it; use heat to raise the pressure.

What does a purge unit do in a low-pressure system?

A purge unit removes air and other noncondensable gases, separates refrigerant from the purge stream, and returns that refrigerant to the system.

What can unusually frequent purge operation indicate?

Frequent or increasing purge operation is a warning sign of possible leakage. Investigate and locate leaks; purging is not a substitute for repair.

What is the commonly taught maximum leak-test pressure for a low-pressure centrifugal chiller?

For Type III exam preparation, 10 psig is the commonly taught maximum leak-test pressure for a low-pressure centrifugal chiller. Treat it as a ceiling, not a target.