CARO - Certified Assistant Refrigeration Operator Compressor Operation and Maintenance Questions and Answers

Question 1

An operator notices excessive vibration and a new, unusual noise coming from a reciprocating compressor during operation. Which of the following is the most likely immediate cause for this issue?

Accepted Answer

Slugging of liquid refrigerant

Answer

Slugging occurs when liquid refrigerant enters the compressor's cylinder. Since liquids are incompressible, this causes a sudden, violent hydraulic shock, leading to severe vibration, loud knocking noises, and potentially catastrophic damage to internal components like valves, pistons, and connecting rods.

Question 2

During a routine maintenance check on a screw compressor used in an ammonia refrigeration system, an operator finds that the oil in the separator is milky and foamy. What is the most probable cause of this condition?

Accepted Answer

The oil is contaminated with moisture/water.

Answer

In ammonia refrigeration systems, oil that appears milky or foamy is a classic sign of moisture contamination. Water emulsifies with the refrigeration oil, creating this appearance. This contamination reduces the oil's lubricating properties and can lead to corrosion and component failure.

Question 3

Which of the following routine maintenance tasks is most critical for ensuring the long-term health and efficiency of a reciprocating compressor's moving parts?

Accepted Answer

Regularly checking and changing the crankcase oil and filters

Answer

Proper lubrication is essential for the longevity of any reciprocating compressor. Regularly checking the oil level and changing the oil and filters according to the manufacturer's schedule prevents premature wear of critical components like pistons, cylinders, and bearings by ensuring they are properly lubricated and cooled.

Question 4

An operator needs to perform maintenance that requires opening up a compressor to the atmosphere. What is the critical first step in the pump-down procedure before any components are loosened?

Accepted Answer

Slowly throttle the suction stop valve to lower crankcase pressure.

Answer

Before isolating the compressor, it's crucial to run it and slowly close the suction stop valve. This process, known as pumping down the compressor, safely removes most of the refrigerant from the crankcase. Doing this slowly prevents oil from foaming violently and being carried out of the compressor, which can happen if the pressure is dropped too quickly.

Question 5

A screw compressor is consistently tripping on its high-temperature safety cutout. The condenser appears to be operating normally, and the refrigerant charge is correct. Which of the following maintenance issues is the most likely cause?

Accepted Answer

A dirty or clogged oil cooler/filter

Answer

In a screw compressor, oil is used not only for lubrication but also for cooling and sealing the rotors. If the oil cooler or oil filter is dirty or clogged, oil flow will be restricted, and its cooling efficiency will be greatly reduced. This leads to the compressor overheating and tripping the high-temperature safety control.

CARO - Certified Assistant Refrigeration Operator Practice Test

CARO - Certified Assistant Refrigeration Operator Practice Test

CARO - Certified Assistant Refrigeration Operator Compressor Operation and Maintenance Questions and Answers