CARO Refrigeration System Troubleshooting and Diagnosis 1 — Questions and Answers
Question 1: A refrigeration system has high suction pressure and high discharge pressure. What is the most likely cause?
- Refrigerant undercharge
- Dirty or fouled condenser reducing heat rejection (Correct answer)
- Expansion valve too far closed
- Compressor valve failure
Correct answer: Dirty or fouled condenser reducing heat rejection
A dirty condenser restricts heat rejection, causing both condensing pressure (discharge) and suction pressure to rise as the system struggles to remove heat from the refrigerant.
Question 2: Low suction pressure and low discharge pressure on an ammonia system most likely indicates what condition?
- Overcharge of refrigerant
- Undercharge of refrigerant or low refrigerant level (Correct answer)
- Dirty condenser
- High ambient temperature
Correct answer: Undercharge of refrigerant or low refrigerant level
A low refrigerant charge causes both suction and discharge pressures to drop because there is insufficient refrigerant mass circulating through the system.
Question 3: A technician notices frost forming on the suction line all the way back to the compressor. What does this indicate?
- Normal operation for a low-temperature system
- Liquid refrigerant is flooding back to the compressor (liquid slugging risk) (Correct answer)
- The evaporator is operating efficiently
- The system is overcharged with oil
Correct answer: Liquid refrigerant is flooding back to the compressor (liquid slugging risk)
Frost or ice on the suction line back toward the compressor indicates liquid refrigerant is not fully vaporizing in the evaporator and flooding back, which can cause severe compressor damage.
Question 4: High discharge temperature with normal suction pressure on an ammonia compressor most likely indicates what problem?
- Low refrigerant charge
- High suction superheat or discharge valve inefficiency (Correct answer)
- Wet suction (liquid flood-back)
- Low condenser water temperature
Correct answer: High suction superheat or discharge valve inefficiency
High discharge temperature with normal suction pressure often points to excessive suction superheat, leaking discharge valves, or high compression ratio, all of which cause the discharge gas to overheat.
Question 5: What symptom would indicate that a thermostatic expansion valve (TXV) is stuck closed?
- High suction pressure and flooding evaporator
- Low suction pressure, warm suction line, and starved evaporator (Correct answer)
- High discharge pressure and normal suction pressure
- Liquid returning to compressor
Correct answer: Low suction pressure, warm suction line, and starved evaporator
A TXV stuck closed starves the evaporator of refrigerant, resulting in low suction pressure, a warm suction line, and reduced cooling capacity.
Question 6: Oil accumulation in the evaporator of an ammonia system causes which operational problem?
- Increased refrigerant flow
- Reduced heat transfer efficiency and higher evaporating temperature (Correct answer)
- Lower discharge pressure
- Improved system lubrication
Correct answer: Reduced heat transfer efficiency and higher evaporating temperature
Oil coating the evaporator heat transfer surfaces acts as an insulator, reducing heat transfer effectiveness and forcing the system to operate at a lower evaporating temperature to maintain the load.
CARO Refrigeration System Troubleshooting and Diagnosis 1
A refrigeration system has high suction pressure and high discharge pressure.
What is the most likely cause?