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
A locomotive engineer is required to log a cab environment defect. Which of the following would NOT typically be considered an HVAC defect requiring a notation?
Answer: Cab temperature 2°F above the preferred engineer comfort level during mild weather
A minor temperature variance within the acceptable comfort range during mild weather is not typically a reportable HVAC defect, unlike system failures affecting safety.
What is the function of the low-pressure cutout switch in a locomotive AC system?
Answer: It prevents the compressor from starting unless refrigerant pressure is sufficient
The low-pressure cutout switch prevents compressor operation when refrigerant pressure is too low, protecting the compressor from running without adequate lubrication.
When must a locomotive engineer report an HVAC system defect using a locomotive defect card (FRA Form 6180.49a)?
Answer: Immediately upon discovering any defect that affects the safety or proper operation of required equipment
FRA regulations require that defects affecting safety or required equipment be recorded on the defect card as soon as they are discovered.
What is the purpose of maintaining positive cab pressure in a locomotive HVAC system?
Answer: To prevent diesel exhaust, dust, and other contaminants from infiltrating the cab through gaps
Positive cab pressure ensures that air leaks outward rather than inward, preventing diesel exhaust and contaminants from entering the cab.
Which component transfers heat from the refrigerant to the outside environment in a locomotive AC system?
Answer: Condenser
The condenser releases heat absorbed from the cab air by the evaporator into the outside environment, completing the refrigeration cycle.
A locomotive engineer operating in a mountainous region notices the AC system produces adequate cooling at lower elevations but struggles above 7,000 feet. The most probable cause is:
Answer: Reduced air density limiting condenser heat rejection capacity
At high elevation, thinner air reduces condenser efficiency because less air mass passes over the coil, limiting heat rejection capacity.
What action should a locomotive engineer take if the carbon monoxide alarm in the cab activates during operations?
Answer: Immediately switch to 100% fresh outside air, notify the dispatcher, and prepare to stop if CO levels remain elevated
A CO alarm requires immediately maximizing fresh air intake to dilute CO, notifying the dispatcher, and preparing to stop if the situation does not improve.