CRST Troubleshooting & Repair Techniques 2

Question 1

A refrigeration system is short-cycling on the low-pressure control. What is the MOST likely cause?

Accepted Answer

Low refrigerant charge

Answer

A low refrigerant charge causes suction pressure to drop below the low-pressure control cutout setpoint, causing repeated short cycling.

Question 2

A technician measures a 15°F superheat at the evaporator outlet and 80°F subcooling at the condenser outlet. What condition does this indicate?

Accepted Answer

Refrigerant overcharge

Answer

Excessive subcooling combined with normal or low superheat is a classic sign of refrigerant overcharge in the system.

Question 3

When checking a hermetic compressor for an open motor winding, which instrument should be used?

Accepted Answer

Ohmmeter

Answer

An ohmmeter measures resistance between terminals to identify an open winding, which shows infinite or very high resistance.

Question 4

A walk-in cooler is not maintaining setpoint even though the compressor runs continuously. The evaporator coil is heavily frosted. What is the FIRST action to take?

Accepted Answer

Defrost the evaporator coil

Answer

Heavy frost blocks airflow across the evaporator, reducing heat transfer efficiency; defrosting restores normal operation before further diagnosis.

Question 5

Oil logging in the evaporator of a low-temperature system is MOST likely caused by:

Accepted Answer

Insufficient refrigerant velocity to return oil

Answer

At low temperatures, refrigerant vapor density decreases, and if velocity is too low, oil cannot be carried back to the compressor crankcase.

(CRST) Certified Refrigeration Service Technician Practice Test

(CRST) Certified Refrigeration Service Technician Practice Test

CRST Troubleshooting & Repair Techniques 2