EPA 608 Type III Study Guide (Low-Pressure Chillers)

Type III covers low-pressure appliances, mainly centrifugal chillers using refrigerants such as R-123, R-11 (older) and R-1233zd. You also need Core.

How low-pressure systems are different

• The evaporator (low side) runs below atmospheric pressure, in a vacuum.
• So when there's a leak, air and moisture leak in; refrigerant doesn't leak out on the low side.
• Air and moisture are non-condensables. They raise head pressure, cut efficiency and cause acids.

Purge units

• The purge unit removes non-condensables (air and moisture) from the condenser.
• High-efficiency purge units release very little refrigerant.
• Purge run time is your leak indicator. If the purge runs more than usual, air is getting in somewhere.

Required evacuation level

For recovery equipment made after November 15, 1993, low-pressure appliances must be evacuated to 25 mm Hg absolute (about 29 in. Hg vacuum). That's far deeper than high-pressure systems require.

Recovery

• Recover the liquid first, then the vapor. A large chiller can hold hundreds of pounds of refrigerant as vapor after the liquid is gone.
• Keep water moving through the tubes (or drain them) during recovery. As pressure drops, refrigerant temperature drops, and water in the tubes can freeze and rupture them.
• Recovery machines for low-pressure systems are built to handle large vapor volumes and deep vacuums, often with water-cooled condensers.

Leak testing

• Raise the system pressure with controlled hot water or heating blankets, or with nitrogen.
• Never exceed 10 psig. The evaporator's rupture disc is typically set at 15 psig.

Charging

• From a deep vacuum, charge vapor first until the pressure reaches the saturation pressure for about 32°F, so water in the tubes doesn't freeze.
• Then charge liquid through the evaporator charging valve.

Leak repair

Chillers used for comfort cooling fall under the 10% per year threshold (20% commercial refrigeration, 30% industrial process). Repairs are generally due within 30 days, followed by verification tests.

Safety

• R-123 is class B1: higher toxicity, no flame propagation.
• Equipment rooms need refrigerant monitors, alarms and ventilation per ASHRAE Standard 15.
• Use proper PPE; recover before opening the system.

Quick review

• Low side in a vacuum: leaks pull air in.
• Purge run time signals leaks.
• Evacuate to 25 mm Hg absolute.
• Leak test at 10 psig or less (rupture disc 15 psig).
• Circulate or drain water during recovery and charge vapor first to prevent freezing.