Heating, Ventilation & AC Flashcards
7 cards from real LEC practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Heating, Ventilation & AC flashcards as text
What happens to air conditioning system performance at very high altitudes during locomotive operations?
Answer: Performance decreases because lower air density reduces heat exchanger efficiency
At high altitudes, lower air density reduces the efficiency of condenser heat rejection, decreasing overall AC system performance.
A locomotive cab heater uses diesel fuel drawn from the main tank. What safety concern does this introduce?
Answer: A heater malfunction or fuel leak creates a fire risk near ignition sources
Diesel-fueled cab heaters introduce fire risk if a leak occurs near ignition sources, making regular inspection critical.
Which component in a locomotive HVAC system is responsible for removing humidity from cab air?
Answer: The evaporator coil
The evaporator coil cools air below its dew point, causing moisture to condense on the coil and be drained away, reducing cab humidity.
An engineer is operating in a tunnel and notices reduced cab ventilation. Why is maintaining adequate ventilation especially critical in tunnels?
Answer: Diesel exhaust and carbon monoxide can accumulate in enclosed tunnel environments
In tunnels, diesel exhaust and CO can accumulate rapidly, making adequate ventilation critical to prevent crew exposure to toxic gases.
What is the function of the thermostatic expansion valve (TXV) in a locomotive AC refrigeration cycle?
Answer: It meters refrigerant flow into the evaporator to maintain optimal superheat
The TXV regulates refrigerant flow into the evaporator to maintain the correct superheat level, ensuring efficient and safe system operation.
During pre-trip inspection, an engineer finds the cab heater blower motor running but no heat is being produced. What is the most likely cause?
Answer: The heater fuel valve or igniter has failed, preventing combustion
If the blower runs but no heat is produced, the combustion process has failed — typically due to a faulty fuel valve or igniter.
What is the role of the receiver-drier in a locomotive AC system?
Answer: It stores liquid refrigerant and removes moisture to protect system components
The receiver-drier stores a reserve of liquid refrigerant and contains desiccant to absorb moisture that could damage the system.