WHAT TYPE III COVERS
Type III applies to low-pressure appliances:
• Operate below atmospheric pressure
• Common refrigerants: R-11, R-123, R-113, R-245fa
• Typical systems: centrifugal chillers, absorption chillers
LOW-PRESSURE REFRIGERANT CHARACTERISTICS
• Boiling points: very low pressure, often vacuum
• Systems operate in a vacuum (psia), not psig
• Any leaks pull air and moisture INTO the system
• Moisture creates acids → damages oil, tubes, and windings
LEAK DETECTION
• Soap bubbles and electronic detectors approved
• Most important sign: Rising purge unit run time
• High purge run time = system pulling in non-condensables (air)
• Non-condensables raise head pressure in condenser
• Air IN instead of refrigerant OUT
LEAK TESTING PRESSURE LIMITS
• NEVER pressurize a low-pressure system above 10 psig
• Doing so may rupture rupture discs
• Normal leak test pressure: ~1–10 psig nitrogen
• Use nitrogen ONLY, never oxygen or compressed air
SAFETY RELIEF DEVICES
• Typical burst/rupture disc pressure: 15 psig
• Discharge line must vent to outside building
• Never install multiple relief valves in series
• Always installed in parallel
VACUUM & EVACUATION LEVELS
Target recovery level (for disposal):
• 25 mm Hg absolute (deep vacuum)
If system leaks and cannot achieve 25 mm Hg:
• Recover to as low as possible, but not below atmospheric
• Then retrofit, repair, or retire
When dehydrating system:
• Pull vacuum to 500 microns
• Micron gauge required
• If vacuum rises:
- Slowly → moisture
- Rapidly → leak
COMPONENTS TO KNOW
Purge Unit:
• Removes air and non-condensables pulled into system
• High purge run time = LEAK present
Refrigerant Charging Unit (RCU):
• Used to transfer refrigerant from system to drum or back
Rupture Disc:
• Protects system from overpressure
• Breaks at ~15 psig
• Connected to vent line
Water Boxes:
• Must be opened/drained before recovery
• Removing water reduces pressure and prevents freezing
Oil Removal Equipment:
• Heated oil separators or pump-out units
• Required because oil often contains large amounts of refrigerant
RECOVERY & EVACUATION PROCEDURES
Before recovery:
• Drain water sides of evaporator & condenser
• Open water box access covers
• Isolate chiller
• Connect recovery equipment
During recovery:
• Expect very slow vapor recovery (low pressure refrigerants)
• Heating the chiller or using warm water helps raise pressure
• Maintain water flow to avoid freezing
• Never raise pressure over 10 psig
After recovery:
• Pull vacuum to 25 mm Hg absolute
• If cannot reach that → recover to 0 psig and tag as “leaking”
CHARGING LOW-PRESSURE SYSTEMS
• Charging begins in a vacuum
• Start by charging liquid refrigerant into the condenser
• This raises system pressure enough to avoid freezing the chiller barrel
• Once pressure is above 0 psig, vapor or liquid can be added
Never charge with refrigerant at pressures above 10 psig into low-pressure chillers.
RECOVERY LEVELS FOR TYPE III
Required recovery levels (before opening system):
• For disposal: 25 mm Hg absolute
• If system leaks: recover to atmospheric pressure
• Never exceed 10 psig during pressurization
REFRIGERANT CHARACTERISTICS (for questions)
R-11 and R-123 are low-pressure refrigerants.
R-123 typically operates around:
• 1.5 in Hg vacuum (evaporator)
• 5–7 psig (condenser)
Low-pressure refrigerants often have:
• High boiling points
• Operate in vacuum
• High ozone depletion potential (older refrigerants)
KEY TRIGGER PHRASES FOR THE EXAM
“System operates in a vacuum” → Low-pressure system
“Air leaks into system” → Type III
“Purge unit run time high” → Leak
“Pressurize only up to 10 psig” → Safety limit
“Rupture disk breaks at 15 psig” → Safety device
“25 mm Hg absolute” → Final recovery vacuum
“Drain water box before recovery” → Required step
“Charging begins in vacuum” → True
“First add liquid to condenser” → Prevent freezing
“If vacuum rises quickly” → Leak
“If vacuum rises slowly” → Moisture
SAFETY
• Wear goggles and gloves
• Never heat refrigerant cylinders
• Never mix refrigerants
• Always use nitrogen (regulated) for pressure tests
• Ensure purge discharge vents outdoors
• Monitor chiller water temperature to avoid freeze-up
LEGAL REQUIREMENTS
• Technician must have certification before servicing
• Records retained for 3 years
• Illegal to vent refrigerant
• Owners responsible for leak repair compliance