HVAC and Cab Systems Flashcards
7 cards from real 310T practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 HVAC and Cab Systems flashcards as text
On a coach with an automatic temperature control (ATC) system, the cabin temperature does not reach the set point. After verifying refrigerant charge is correct, what should the technician check next?
Answer: ATC sensor calibration, blend door actuator operation, and control module inputs/outputs
ATC systems rely on accurate sensor feedback and properly functioning actuators; a miscalibrated sensor or failed actuator will prevent the system from reaching setpoint even with correct charge.
When flushing a contaminated truck A/C system, what component must NOT be flushed and should be replaced instead?
Answer: Receiver-drier or accumulator
Receiver-driers and accumulators contain desiccant that is destroyed by flushing solvents and must always be replaced when the system is opened or flushed.
A truck cab window fogs repeatedly on the inside despite the defroster being on. What is the most likely HVAC-related cause?
Answer: A leaking heater core introducing moisture into the cabin airstream
A leaking heater core introduces coolant steam into the cabin, significantly increasing humidity and causing persistent interior fogging that defrosting alone cannot overcome.
What is the correct procedure for leak-testing a truck A/C system after repair?
Answer: Pressure-test with dry nitrogen, then evacuate, then charge and verify with an electronic leak detector
Nitrogen pressure testing verifies mechanical integrity without introducing refrigerant, followed by evacuation to remove moisture and air before charging and final leak verification.
A truck's cab air suspension seat is not adjusting properly and the air compressor runs continuously. What should the technician suspect?
Answer: A leak in the seat air bladder or supply line causing the compressor to run without building pressure
A continuously running compressor that cannot build pressure indicates an air leak in the seat's bladder, lines, or fittings that prevents the system from reaching the target height.
In a coach roof-mounted A/C unit, water is dripping into the passenger compartment instead of draining outside. What is the most likely cause?
Answer: Blocked or frozen evaporator condensate drain
Condensate from the evaporator normally drains outside through drain tubes; if these are blocked or frozen, water backs up and leaks into the coach interior.
A 310T technician is evacuating a truck A/C system before recharging. The system will not pull down below 500 microns. What does this indicate?
Answer: A leak in the system or vacuum pump, or moisture present, preventing a deep vacuum
Inability to reach deep vacuum (below 500 microns) indicates a leak that allows air ingress, a faulty vacuum pump, or moisture that keeps vaporizing and raising pressure.