CARO Cheat Sheet 2026

The 30 highest-yield CARO facts, distilled from real exam questions. Print it, save it as a PDF, or study it here — free, no sign-up.

1. Why is ammonia's strong odor considered a safety advantage? → It provides warning at concentrations far below dangerous levels
2. Why must a screw compressor have a discharge check valve? → To prevent backflow of high-pressure gas that could spin the rotors in reverse at shutdown
3. A small ammonia leak is found at a valve packing; what is the best environmental compliance practice? → Document it, isolate if needed, and repair it promptly
4. According to the ASHRAE refrigerant safety classification system, what does the designation 'B2L' indicate about a refrigerant like ammonia (R-717)? → Higher toxicity, mildly flammable
5. What is the OSHA permissible exposure limit (PEL) for ammonia as an 8-hour time-weighted average? → 50 ppm
6. What component typically controls capacity on most industrial rotary screw compressors? → A slide valve that changes the effective rotor length used for compression
7. A system runs at 150 psig discharge and 15 psig suction at sea level. What is the approximate compression ratio? → 5.5
8. An operator closes valves on both ends of a liquid ammonia line without a relief path. What hazard is created? → Hydrostatic expansion that can rupture the pipe
9. What is a common sign that noncondensable gases are in a refrigeration system? → Higher-than-normal head pressure for the condensing temperature
10. Under ANSI/IIAR guidance, how often should pressure relief valves on ammonia systems typically be replaced? → Every 5 years
11. Before starting a screw compressor, the slide valve should normally be positioned at: → Minimum load (fully unloaded)
12. For a saturated refrigerant (liquid and vapor present together), what is true about pressure and temperature? → Each pressure corresponds to one specific temperature
13. In an evaporative condenser, how is heat primarily rejected from the refrigerant? → By evaporation of water sprayed over the coil while air is drawn through
14. Where is an oil separator normally installed in a vapor-compression system? → In the discharge line between the compressor and condenser
15. In an ammonia system, where does mineral refrigeration oil tend to collect? → At low points, because oil is heavier than liquid ammonia and does not mix
16. Which type of heat exchanger is commonly used as a compact evaporator in liquid chillers? → Plate heat exchanger
17. Which code organization publishes standards such as ANSI/IIAR 2 for safe design of ammonia refrigeration systems? → IIAR
18. What problem can result from over-greasing an electric motor bearing? → Overheating and possible seal or winding damage
19. An operator feels a noticeable temperature drop across a liquid line filter-drier. What does this most likely indicate? → The drier is restricted and causing a pressure drop
20. A refrigeration system has high suction pressure and high discharge pressure. What is the most likely cause? → Dirty or fouled condenser reducing heat rejection
21. A flooded-type shell-and-tube evaporator is being used to chill brine. Where are the refrigerant and the brine typically located within this component? → The brine is in the tubes, and the refrigerant is in the shell.
22. A pilot-operated pressure regulating valve (PRV) in refrigeration is used to: → Automatically maintain a set downstream pressure regardless of upstream pressure changes
23. What is the OSHA permissible exposure limit (PEL) for ammonia as an 8-hour time-weighted average? → 50 ppm
24. In a water-cooled shell-and-tube condenser, where does the refrigerant typically flow? → In the shell, around the tubes carrying water
25. Scale buildup inside the water tubes of a water-cooled condenser will most likely result in what? → Higher condensing pressure
26. Which tool is commonly used to check compressor-to-motor coupling alignment? → A dial indicator or laser alignment system
27. Which respirator is required when entering an area with an unknown ammonia concentration? → Self-contained breathing apparatus (SCBA)
28. Which of the following conditions would most likely cause an evaporator to become 'starved' of refrigerant? → A dirty or clogged filter-drier upstream of the expansion device.
29. Which IIAR document gives the labeling standard for identifying ammonia piping, including the contents, physical state, pressure level and flow direction? → IIAR Bulletin 114 / IIAR 6
30. On a reciprocating ammonia compressor, how do cylinder unloaders typically reduce capacity? → By holding the suction valves open so the cylinder does not compress gas