CARO Preventive Maintenance 2 — Questions and Answers
Question 1: What is the most reliable reference for the correct running oil level in a reciprocating compressor sight glass?
- The level observed when the compressor was last shut down
- The compressor manufacturer's specifications (Correct answer)
- A full sight glass at all times
- The level recorded by the previous shift, regardless of conditions
Correct answer: The compressor manufacturer's specifications
Correct oil level varies by machine design, so the manufacturer's specification is the authoritative reference.
Question 2: A V-belt drive is being checked during routine maintenance. What is the common rule of thumb for proper belt deflection?
- 1/64 inch per inch of span (Correct answer)
- 1/4 inch per inch of span
- 1 inch regardless of span
- No deflection at all
Correct answer: 1/64 inch per inch of span
A deflection of about 1/64 inch per inch of span is the widely used guideline for V-belt tension.
Question 3: An operator feels a noticeable temperature drop across a liquid line filter-drier. What does this most likely indicate?
- The drier is working normally at full capacity
- The system is overcharged with oil
- The drier is restricted and causing a pressure drop (Correct answer)
- The condenser is undersized
Correct answer: The drier is restricted and causing a pressure drop
A temperature drop across a drier indicates a pressure drop and flashing caused by a restriction.
Question 4: In a halocarbon system, a moisture-indicating sight glass shows yellow instead of green. What should the operator conclude?
- The system has too much refrigerant
- The refrigerant is dry and in good condition
- The sight glass needs to be cleaned
- Moisture is present and the drier may need changing (Correct answer)
Correct answer: Moisture is present and the drier may need changing
On most indicators, yellow (or pink) means wet while green (or blue) means dry.
Question 5: Why is vibration data on compressors and pumps trended over time rather than checked only once?
- To detect gradual changes that signal developing bearing, alignment, or balance problems (Correct answer)
- To satisfy the electric utility's demand requirements
- To calculate refrigerant charge
- To determine the refrigerant's saturation temperature
Correct answer: To detect gradual changes that signal developing bearing, alignment, or balance problems
Trending reveals changes from a baseline, allowing repairs before a failure occurs.
Question 6: A routine oil acid test on a halocarbon compressor comes back positive. What does this most likely indicate?
- The oil is new and needs a break-in period
- Moisture contamination or a motor burnout has produced acids (Correct answer)
- The compressor is short of oil
- The suction pressure is too high
Correct answer: Moisture contamination or a motor burnout has produced acids
Acid in the oil typically results from moisture or a motor burnout and requires corrective cleanup.
Question 7: Which symptom most directly results from a fouled or dirty condenser surface?
- Lower discharge pressure
- Lower compressor amperage
- Higher head pressure (Correct answer)
- Lower discharge temperature
Correct answer: Higher head pressure
Fouling reduces heat rejection, raising condensing pressure and compressor work.
CARO Preventive Maintenance 2
What is the most reliable reference for the correct running oil level in a reciprocating compressor sight glass?