LEC Heating, Ventilation & AC 3

Question 1

What happens to air conditioning system performance at very high altitudes during locomotive operations?

Accepted Answer

Performance decreases because lower air density reduces heat exchanger efficiency

Answer

At high altitudes, lower air density reduces the efficiency of condenser heat rejection, decreasing overall AC system performance.

Question 2

A locomotive cab heater uses diesel fuel drawn from the main tank. What safety concern does this introduce?

Accepted Answer

A heater malfunction or fuel leak creates a fire risk near ignition sources

Answer

Diesel-fueled cab heaters introduce fire risk if a leak occurs near ignition sources, making regular inspection critical.

Question 3

Which component in a locomotive HVAC system is responsible for removing humidity from cab air?

Accepted Answer

The evaporator coil

Answer

The evaporator coil cools air below its dew point, causing moisture to condense on the coil and be drained away, reducing cab humidity.

Question 4

An engineer is operating in a tunnel and notices reduced cab ventilation. Why is maintaining adequate ventilation especially critical in tunnels?

Accepted Answer

Diesel exhaust and carbon monoxide can accumulate in enclosed tunnel environments

Answer

In tunnels, diesel exhaust and CO can accumulate rapidly, making adequate ventilation critical to prevent crew exposure to toxic gases.

Question 5

What is the function of the thermostatic expansion valve (TXV) in a locomotive AC refrigeration cycle?

Accepted Answer

It meters refrigerant flow into the evaporator to maintain optimal superheat

Answer

The TXV regulates refrigerant flow into the evaporator to maintain the correct superheat level, ensuring efficient and safe system operation.

(LEC) Locomotive Engineer Certification Practice Test