WALMART MAINTENANCE HVAC and Refrigeration 4 — Questions and Answers
Question 1: What condition is indicated when an air conditioning system has frost forming on the suction line back to the compressor?
- Refrigerant overcharge
- Low airflow across the evaporator or low refrigerant charge (Correct answer)
- Faulty condenser fan motor
- High ambient temperature condition
Correct answer: Low airflow across the evaporator or low refrigerant charge
Frost on the suction line indicates the evaporator is too cold due to insufficient airflow over it or a low refrigerant charge, causing moisture to freeze.
Question 2: What is the correct procedure before opening a refrigerant circuit for repairs in a commercial system?
- Purge the system with nitrogen and begin work
- Recover the refrigerant using EPA-certified equipment (Correct answer)
- Vent the refrigerant outdoors in a well-ventilated area
- Allow the system to equalize pressure naturally before opening
Correct answer: Recover the refrigerant using EPA-certified equipment
EPA Section 608 regulations require that refrigerant be recovered using certified equipment before opening any refrigerant circuit.
Question 3: A rooftop unit's condenser coil is reading significantly higher head pressure than normal on a mild day. What is the MOST likely cause?
- Low refrigerant charge
- Dirty or blocked condenser coil restricting airflow (Correct answer)
- Faulty evaporator fan motor
- Refrigerant undercharge
Correct answer: Dirty or blocked condenser coil restricting airflow
A dirty or blocked condenser coil reduces heat rejection efficiency, causing head pressure to rise even in mild outdoor temperatures.
Question 4: In a Walmart refrigeration rack system, what is the function of a suction pressure regulator (SPR)?
- To boost suction pressure to the compressor during peak load
- To limit evaporator pressure to prevent product from thawing (Correct answer)
- To maintain minimum condensing pressure in cold weather
- To regulate discharge pressure to the condenser
Correct answer: To limit evaporator pressure to prevent product from thawing
A suction pressure regulator limits evaporator pressure on higher-temperature cases so the compressor rack doesn't pull them down too cold.
Question 5: What does MERV rating indicate on an HVAC air filter?
- The filter's moisture resistance value
- The filter's minimum efficiency reporting value for particle capture (Correct answer)
- The maximum equipment run value before replacement
- The motor efficiency rating value for filter fans
Correct answer: The filter's minimum efficiency reporting value for particle capture
MERV (Minimum Efficiency Reporting Value) rates how effectively a filter captures airborne particles — higher MERV means finer filtration.
Question 6: When checking refrigerant charge using the subcooling method on a TXV system, where is subcooling measured?
- At the evaporator outlet
- At the compressor discharge port
- At the liquid line leaving the condenser (Correct answer)
- At the suction line near the compressor
Correct answer: At the liquid line leaving the condenser
Subcooling is measured at the liquid line leaving the condenser by comparing the actual liquid temperature to the saturation temperature at that pressure.
Question 7: Which type of defrost system uses hot refrigerant gas from the compressor discharge to melt evaporator frost?
- Electric resistance defrost
- Hot gas defrost (Correct answer)
- Off-cycle defrost
- Water defrost
Correct answer: Hot gas defrost
Hot gas defrost routes high-temperature discharge gas through the evaporator coil to rapidly melt frost without using electric heaters.
WALMART MAINTENANCE HVAC and Refrigeration 4
What condition is indicated when an air conditioning system has frost forming on the suction line back to the compressor?