CRST Troubleshooting & Repair Techniques 5

Question 1

A heat pump in heating mode has frost building up on the outdoor coil when outdoor temperature is above 40°F. What is the MOST likely cause?

Accepted Answer

Low refrigerant charge reducing evaporating temperature

Answer

A low refrigerant charge drops the evaporating temperature below the frost point even in mild weather, causing premature frost accumulation on the outdoor coil.

Question 2

A technician uses electronic leak detection and finds a leak at the evaporator coil. What is the NEXT step before brazing the repair?

Accepted Answer

Recover the refrigerant from the system

Answer

Before any brazing or open-flame work, refrigerant must be completely recovered to prevent combustion of refrigerant decomposition products and to comply with EPA regulations.

Question 3

What is the MOST effective way to remove non-condensables from a refrigeration system?

Accepted Answer

Recover refrigerant, evacuate the system, and recharge with virgin refrigerant

Answer

Non-condensables cannot be separated in the field; the only correct method is full recovery, deep evacuation to remove air and moisture, and recharge with new refrigerant.

Question 4

A compressor with a cracked discharge valve reed will MOST likely exhibit:

Accepted Answer

Low compression ratio and elevated suction pressure

Answer

A cracked discharge valve allows high-pressure gas to re-expand into the cylinder, reducing pumping efficiency and causing elevated suction pressure and low compression ratio.

Question 5

When troubleshooting a system that repeatedly trips on high-pressure cutout, the technician should inspect the:

Accepted Answer

Condenser airflow, refrigerant charge, and non-condensables

Answer

High head pressure is caused by poor condenser heat rejection from blocked airflow, refrigerant overcharge, or non-condensables — all three must be checked.

(CRST) Certified Refrigeration Service Technician Practice Test

(CRST) Certified Refrigeration Service Technician Practice Test

CRST Troubleshooting & Repair Techniques 5