Fundamentals & Cycle
30%of exam
Compressors & Lubrication
32%of exam
Heat Exchangers & Purging
26%of exam
Safety & Compliance
12%of exam
Quick Facts
- Exam
- RETA CARO
- Credential
- Asst Refrigeration Operator
- Time
- 3 hours
- Pass
- 70%
- Questions
- 110 multiple-choice
- Refrigerant
- R-717 (ammonia)
- Level
- Entry, no experience
- Fee 2026
- $570 member, $865 nonmember
Cycle Flow Order
Compress, Condense, Expand, Evaporate, repeat
Compressor: raise pressureCondenser: reject heatExpansion valve: drop pressureEvaporator: absorb heat
High Side vs Low Side
High side
- Compressor discharge to TXV inlet
- Condenser, receiver, discharge line
- Higher pressure and temperature
Low side
- TXV outlet to compressor suction
- Evaporator, suction line, accumulator
- Lower pressure and temperature
Split is at metering device
Which Component Handles This
- Need to absorb heat→Evaporator
- Need to reject heat→Condenser
- Need pressure/temp boost→Compressor
- Need pressure drop to low side→Expansion valve
- Store high-pressure liquid→Receiver
- Remove oil from discharge gas→Oil separator
- Remove trapped air/non-condensables→Purger
- Prevent liquid entering compressor→Accumulator
Refrigeration Fundamentals
- Ton
- 12,000 Btu/hr
- Btu
- Heat unit
- Sensible heat
- Changes temperature
- Latent heat
- Changes state, not temp
- Superheat
- Above saturation, vapor side
- Subcooling
- Below saturation, liquid side
Pressure-Temperature Law
Higher pressure always means higher saturation temp
Use for troubleshootingRead gauge, find tempConfirms proper charge level
Vapor-Compression Cycle
- Compressor
- Raises pressure and temp
- Condenser
- Rejects heat, high side
- Expansion valve
- Drops pressure to low side
- Evaporator
- Absorbs heat, low side
- Flow order
- Comp-Cond-Expand-Evap-Comp
Ammonia Physical Properties
- ASHRAE ID
- R-717
- Boiling point
- -28°F at atmospheric
- Vapor density
- 0.6, lighter than air
- Liquid specific gravity
- 0.62, lighter than water
- Ignition temp
- 1,204°F
- Flammable range
- 15-28% in air
- Odor threshold
- 5-50 ppm
- Refrigerant-grade purity
- 99.95%+ ammonia
Saturated Pressure-Temperature
- -28°F
- 0 psig, atmospheric boil
- 0°F
- 16 psig
- 68°F
- 110 psig
- 100°F
- 198 psig
- P-T rule
- Higher temp = higher pressure
Refrigerant Purity Limits
Water 33 ppm max, oil 2 ppm max
Water: freezes, cracks pipingOxygen: stress-corrosion riskOil: fouls heat transferTest periodically for purity
Reciprocating vs Screw Compressor
Reciprocating
- Pistons, positive displacement
- Best at high pressure ratios
- Unloaders step capacity
Screw
- Rotors, continuous compression
- Best at high volume flow
- Slide valve modulates capacity
Piston strokes vs rotor mesh
Troubleshooting Symptom Picker
- High head pressure, clean condenser→Check for non-condensables(Purge system)
- Low suction, frosted coil→Check TXV or charge
- Compressor short cycles rapidly→Check low-pressure control
- Knocking noise at startup→Suspect liquid slugging
- Low net oil pressure→Check oil charge, filter
- Rising pressure, condenser clean→Suspect trapped air
- Cooler warm, coil iced→Check defrost cycle
Compressor Types
- Reciprocating
- Piston, positive displacement
- Screw (rotary)
- Continuous, oil-flooded rotors
- Centrifugal
- High-volume, low-pressure-rise
- Scroll
- Orbiting spiral, small capacity
Oil Separator vs Purger
Oil separator
- Removes oil from hot gas
- Located after compressor discharge
- Returns oil to system
Purger
- Removes air/non-condensables
- Located at condenser/receiver high point
- Vents gas, saves ammonia
Oil vs trapped air removal
Compressor Operation & Controls
- Compression ratio
- Absolute discharge / absolute suction
- Volumetric efficiency
- Actual / theoretical displacement
- Unloaders
- Reduce startup/part-load capacity
- Slide valve
- Screw compressor capacity control
- Liquid slugging
- Liquid enters cylinder, damages valves
- Short cycling
- Frequent start-stop, control fault
Lubrication & Oil Management
- Ammonia-oil miscibility
- Not miscible, oil settles
- Oil separator
- Removes oil from discharge gas
- Oil pot
- Low-point oil collection, draining
- Net oil pressure
- Discharge minus crankcase pressure
- Safe oil draining
- Relieve pressure, PPE, slow bleed
- Synthetic oil
- Better low-temp flow
Flooded vs DX Evaporator
Flooded
- Liquid-full coil, float control
- High efficiency, needs surge drum
- Common on large systems
DX (dry expansion)
- TXV controls superheat, not level
- Simpler, less ammonia charge
- Common on smaller systems
Control point: level vs superheat
Evaporators & Cooling Units
- DX evaporator
- Superheat-controlled by TXV
- Flooded evaporator
- Liquid-full, float level control
- Frost buildup
- Insulates, reduces heat transfer
- Defrost
- Removes frost, restores capacity
- Accumulator
- Traps liquid before compressor
Defrost Methods
- Hot gas defrost
- Discharge gas heats coil
- Water defrost
- Spray water over coil
- Electric defrost
- Resistance heaters melt frost
- Air defrost
- Fans only, mild loads
Condensers & Receivers
- Evaporative condenser
- Water spray plus airflow
- Air-cooled condenser
- Fans only, no water
- High-pressure receiver
- Stores liquid after condenser
- King valve
- Receiver liquid outlet valve
- Relief valve
- Vents overpressure to atmosphere/flare
Purging Non-Condensables
- Non-condensables
- Air, trapped gas in system
- Symptom
- High head pressure, poor cooling
- Purger
- Automatically vents trapped air
- Verification
- Check purge log, discharge rate
Exposure Limit Ladder
Odor, then PEL, STEL, IDLH rising
Odor: 5-50 ppm warnsPEL: 50 ppm 8-hrSTEL: 35 ppm 15-minIDLH: 300 ppm, escape now
PSM vs RMP
OSHA PSM
- 29 CFR 1910.119
- Protects workers on-site
- Enforced by OSHA
EPA RMP
- 40 CFR Part 68
- Protects surrounding community
- Enforced by EPA
Same 10,000 lb trigger, different focus
Ammonia Leak Response
- Detector alarm, low level→Investigate, increase ventilation(Below PEL)
- Smell ammonia, unknown source→Don SCBA, evacuate area(Odor threshold ~5ppm)
- Small controllable leak→Isolate valve, ventilate space
- Large uncontrolled release→Evacuate, sound alarm, call ERT
- Concentration near IDLH→SCBA only, no filter mask
- Ammonia vapor cloud, fire risk→Apply water fog, not stream
- Victim exposed, skin/eyes→Flush 15+ min, remove clothing
Ammonia Exposure Limits
- PEL
- 50 ppm, 8-hour TWA
- STEL
- 35 ppm, 15-minute
- IDLH
- 300 ppm
- Odor threshold
- 5-50 ppm, self-warning
PEL vs IDLH
PEL
- 50 ppm, 8-hour average
- Routine daily exposure limit
- Below this, normal operation
IDLH
- 300 ppm
- Immediate danger to life
- Escape without injury only
Daily limit vs escape limit
PPE & Detection
- SCBA
- Required above IDLH
- Chemical suit
- Splash/vapor protection, high exposure
- Fixed detectors
- Continuous ammonia monitoring, alarms
- Water fog
- Knocks down vapor, dilutes
- Eye/face protection
- Goggles plus face shield
PSM & RMP Compliance
- Trigger quantity
- 10,000 lb ammonia
- PSM authority
- OSHA 29 CFR 1910.119
- RMP authority
- EPA 40 CFR 68
- PHA
- Process hazard analysis
- MOC
- Management of change
- Mechanical integrity
- Inspect, test, maintain equipment
IIAR & Code Standards
- IIAR 2
- Safe system design
- IIAR 6
- Inspection, testing, maintenance
- IIAR 7
- Operating procedures
- IIAR 9
- Minimum safety, existing systems
- ASHRAE 15
- Refrigeration safety standard
Common Traps
Ammonia and Oil
Ammonia dissolves easily in water ≠ Ammonia does not mix with oil
PSM vs RMP Focus
PSM protects workers on-site ≠ RMP protects the surrounding community
PEL vs IDLH Meaning
PEL is a routine daily limit ≠ IDLH means leave immediately
High Side vs Low Side
High side runs hot and high-pressure ≠ Low side runs cold and low-pressure
Flooded vs DX Control
Flooded evaporator controls liquid level ≠ DX evaporator controls suction superheat
Oil Separator vs Purger Job
Oil separator returns oil, not gas ≠ Purger vents air, not oil
Compression Ratio vs Efficiency
Ratio compares absolute pressures only ≠ Efficiency compares actual to swept volume
Last Minute
- 1.110 questions, 3 hours, 70% pass
- 2.Ammonia = R-717; boils -28°F
- 3.PEL 50 ppm, IDLH 300 ppm
- 4.PSM/RMP trigger = 10,000 lb ammonia
- 5.Ammonia is NOT miscible with oil
- 6.High side: compressor to TXV inlet
- 7.Flooded = liquid level control; DX = superheat
- 8.SCBA required above IDLH concentration
- 9.Water fog knocks down ammonia vapor
- 10.Purger vents air; separator removes oil
- 11.Fee 2026: $570 member / $865 nonmember
- 12.No experience required; entry-level exam
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