Walmart Maintenance Technician Question and Answers 2 — Questions and Answers
Question 1: A store manager reports that the HVAC system is blowing warm air in the frozen food section. What should you diagnose first?
- Replace the entire HVAC unit
- Check the thermostat settings and refrigerant levels in the zone system (Correct answer)
- Open windows to let cool air in
- Turn off the HVAC system completely
Correct answer: Check the thermostat settings and refrigerant levels in the zone system
Start with the simplest checks: thermostat settings and refrigerant levels before considering component replacement.
HVAC troubleshooting follows a systematic approach. The thermostat may have been inadvertently changed, or the zone damper could be malfunctioning. Low refrigerant indicates a leak that must be found and repaired. Checking these items takes minutes and avoids the cost and downtime of unnecessary component replacement.
Question 2: What does a megohmmeter (megger) test measure in an electric motor?
- Motor speed in RPM
- Insulation resistance between windings and ground (Correct answer)
- Voltage output of the motor
- The temperature of motor bearings
Correct answer: Insulation resistance between windings and ground
A megger test measures insulation resistance, indicating whether motor winding insulation is degraded.
A megohmmeter applies a high DC voltage (typically 500V or 1000V) between the motor windings and the frame/ground. Healthy insulation shows resistance in the megaohm range, while degraded insulation shows lower values. Readings below 1 megaohm generally indicate the motor needs rewinding. This test is essential for predictive maintenance and preventing unexpected motor failures.
Question 3: The parking lot lights on one circuit are out. You check the breaker and it has tripped. After resetting, it trips again immediately. What is the likely cause?
- The breaker is faulty and needs replacement
- There is a short circuit in the wiring or a fixture on that circuit (Correct answer)
- The lights are too bright for the circuit
- The parking lot timer is malfunctioning
Correct answer: There is a short circuit in the wiring or a fixture on that circuit
An immediately re-tripping breaker indicates a short circuit that must be located and repaired before restoring power.
When a breaker trips immediately upon reset, it indicates a short circuit (very low resistance path) rather than an overload. The fault could be in the underground wiring (common with moisture intrusion), a fixture with water damage, or a damaged cable. The circuit must be isolated by disconnecting fixtures one at a time to identify the faulted section before repair.
Question 4: What is the primary reason for performing vibration analysis on rotating equipment?
- To measure the weight of the equipment
- To detect early signs of bearing wear, misalignment, or imbalance (Correct answer)
- To determine the color coding for maintenance schedules
- To measure the electrical consumption
Correct answer: To detect early signs of bearing wear, misalignment, or imbalance
Vibration analysis detects mechanical issues early, allowing planned repairs before catastrophic failure.
Vibration analysis is a cornerstone of predictive maintenance. Different fault conditions produce distinct vibration signatures: imbalance shows 1x running speed, misalignment shows 2x, and bearing defects produce specific frequencies related to bearing geometry. Detecting these patterns early allows maintenance to be scheduled during planned downtime rather than dealing with emergency breakdowns.
Question 5: A automatic sliding door keeps opening and closing on its own with no one nearby. What should you check?
- Replace the door motor
- Check and adjust the motion sensor sensitivity and alignment (Correct answer)
- Disconnect the door and prop it open
- Install a manual door instead
Correct answer: Check and adjust the motion sensor sensitivity and alignment
False triggers from motion sensors are usually caused by sensitivity set too high or sensors aimed at moving objects like signs or trees.
Automatic door motion sensors can be triggered by moving objects in their detection zone: swaying signs, balloons, HVAC drafts moving lightweight objects, or reflected sunlight. Adjusting the sensitivity threshold and realigning the detection zone to exclude these false triggers resolves the issue. Microwave sensors may also need range reduction.
Question 6: When brazing copper refrigeration lines, what gas should be used to prevent internal oxidation?
- Compressed air
- Dry nitrogen (Correct answer)
- Carbon dioxide
- Oxygen
Correct answer: Dry nitrogen
Flowing dry nitrogen through the lines during brazing prevents internal oxidation that can contaminate the refrigeration system.
When copper is heated during brazing, internal surfaces oxidize and form copper oxide scale. These particles can circulate through the refrigeration system, clogging metering devices, filter-driers, and compressor valves. Flowing dry nitrogen at low pressure (2-5 PSI) through the line purges oxygen and prevents scale formation. This is an industry standard practice per ASHRAE and manufacturer guidelines.
Walmart Maintenance Technician Question and Answers 2
A store manager reports that the HVAC system is blowing warm air in the frozen food section.
What should you diagnose first?