CARO Refrigeration System Troubleshooting and Diagnosis 2 — Questions and Answers
Question 1: A compressor is short-cycling (turning on and off rapidly). What is the most common cause?
- Excess refrigerant charge
- Incorrect pressure control setpoint differential or refrigerant undercharge (Correct answer)
- High ambient temperature
- Dirty evaporator coil
Correct answer: Incorrect pressure control setpoint differential or refrigerant undercharge
Short-cycling is often caused by a pressure control with too narrow a differential (cut-in too close to cut-out) or low refrigerant charge causing rapid pressure swings.
Question 2: What does an abnormally high compressor amp draw combined with low suction pressure indicate?
- Normal heavy load operation
- Possible liquid slugging or mechanical issue within the compressor (Correct answer)
- Refrigerant overcharge
- Condenser fouling
Correct answer: Possible liquid slugging or mechanical issue within the compressor
High amp draw with low suction pressure can indicate liquid slugging, worn compressor internals, or tight bearings, all of which cause the motor to work harder than normal.
Question 3: Moisture contamination in a refrigeration system most commonly causes what problem in the expansion device?
- Increased refrigerant flow
- Ice formation that blocks or partially freezes the expansion valve orifice (Correct answer)
- Higher suction pressure
- Compressor valve erosion
Correct answer: Ice formation that blocks or partially freezes the expansion valve orifice
Moisture in the refrigerant freezes at the expansion device orifice where temperature and pressure drop sharply, causing intermittent or permanent blockage and starving the evaporator.
Question 4: When troubleshooting an ammonia system that is not reaching its design suction temperature, what should be checked first?
- Condenser water temperature
- Refrigerant charge level and expansion device operation (Correct answer)
- Compressor oil level
- Electrical phase balance
Correct answer: Refrigerant charge level and expansion device operation
Insufficient refrigerant charge or a malfunctioning expansion device are the most common reasons a system cannot reach its design suction temperature, making these the first things to check.
Question 5: What does a continuously running compressor that never shuts off, combined with a warm refrigerated space, most likely indicate?
- The thermostat setpoint is too low
- Insufficient refrigeration capacity — possible refrigerant loss, dirty coils, or excessive load (Correct answer)
- Normal operation under peak summer conditions
- Oversized compressor
Correct answer: Insufficient refrigeration capacity — possible refrigerant loss, dirty coils, or excessive load
A compressor that runs continuously without achieving the setpoint indicates the system lacks sufficient capacity, which may be due to refrigerant loss, fouled heat exchangers, or an unusually high heat load.
Question 6: Excessive vibration in a reciprocating ammonia compressor is best diagnosed using which method?
- Checking system pressures only
- Visual inspection combined with vibration analysis and listening for unusual mechanical noises (Correct answer)
- Monitoring suction temperature
- Checking refrigerant charge level
Correct answer: Visual inspection combined with vibration analysis and listening for unusual mechanical noises
Vibration analysis and listening for unusual sounds (knocking, rattling) combined with visual inspection help identify loose mounts, worn bearings, valve issues, or liquid slugging causing the vibration.
CARO Refrigeration System Troubleshooting and Diagnosis 2
A compressor is short-cycling (turning on and off rapidly).
What is the most common cause?