Five free practice questions on heating and air conditioning: block I of the Red Seal 310T Truck and Coach Technician exam, about 7 of its 135 questions. They are in the exam's format: four options, one correct answer. Answer each one before opening the explanation. No account, no email.
01The questions
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A driver reports a coach's A/C makes a loud rattling noise when the compressor engages, and cooling is inconsistent. What should the technician suspect first?
- A dirty cab air filter element.
- Compressor or clutch failing.
- Low coolant in the engine.
- Worn windshield wiper blades.
Show the answer
B. Correct. A rattle on engagement is the compressor itself (worn internals, a failing clutch bearing or a loose clutch plate) or liquid slugging, where liquid refrigerant reaches the compressor because of an overcharge or a flooding expansion valve; both produce inconsistent cooling. The RSOS lists noises and poor cooling among A/C symptoms, compressors and expansion valves among components, and listening for compressor engagement among sensory inspections; pressures are checked with gauges and the compressor's oil and clutch inspected before it fails and sends debris through the system.
Why not the others
A. A filter restricts airflow; it does not rattle on compressor engagement.
C. Coolant belongs to the engine and heater, not the A/C compressor.
D. Wipers are unrelated.
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A tractor's cab heater blows only lukewarm air although the engine reaches normal operating temperature and the coolant level is full. The heater inlet hose is hot and the outlet hose is much cooler. What does this indicate?
- Low refrigerant charge in the A/C.
- A restricted core or closed flow valve.
- A worn blower motor with low speed.
- A stuck-open engine coolant thermostat.
Show the answer
B. Correct. With the engine at temperature and the inlet hose hot, coolant is reaching the heater; an outlet hose that is much cooler means little coolant is flowing through the core, so it is either restricted by scale and debris or the coolant flow (shut-off) valve is not opening fully. The RSOS lists no heat and malfunctioning heat controls among symptoms, flow valves and heater cores among components, and feeling air flow and temperature among sensory inspections; the valve is checked for full travel and the core flushed or replaced.
Why not the others
A. Refrigerant is the A/C side and has no effect on heater output.
C. A weak blower reduces airflow, not the temperature difference between the heater hoses.
D. A stuck-open thermostat keeps the engine from reaching temperature; here the engine is normal.
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A tractor's A/C compressor clutch will not engage. The technician finds the low-pressure switch circuit open and the static system pressure very low. What is the most likely cause and the correct action?
- Jump the switch and run the system.
- Add refrigerant until the clutch engages.
- Replace the compressor.
- The charge leaked out; fix the leak.
Show the answer
D. Correct. The low-pressure switch protects the compressor by opening the clutch circuit when the refrigerant pressure is too low to carry oil; a very low static pressure means most of the charge has escaped. The RSOS lists electrical, leakage and pressure among A/C tests and leak detectors among tools; jumping the switch or simply adding refrigerant puts oil-starved load on the compressor and vents the refrigerant again. The leak is found (electronic detector, dye or nitrogen pressure test), repaired, the system evacuated and recharged to specification.
Why not the others
A. Bypassing the protection runs the compressor without oil circulation and destroys it.
B. Topping up a leaking system wastes refrigerant, violates handling rules and leaves the leak.
C. The compressor is being protected, not failed; the leak is the fault.
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A coach's cab blower works only on its highest speed; the lower speeds produce nothing. What is the most likely cause?
- Low coolant in the engine.
- A plugged or scaled heater core.
- Failed resistor or speed module.
- A worn accessory drive belt.
Show the answer
C. Correct. On most systems the highest speed feeds the blower directly while the lower speeds pass through a resistor pack or an electronic speed module that drops the voltage; when it fails open, only high speed works. The RSOS lists resistors, modules and blowers among heating and ventilation components and malfunctioning heat controls among symptoms, with multimeters and breakout harnesses among tools; the technician confirms voltage into and out of the resistor or module at each speed before replacing it, and checks the blower's current draw, because a dragging motor overheats resistors.
Why not the others
A. Coolant level does not affect the blower's electrical speeds.
B. A restricted core affects heat, not blower speeds.
D. The blower is electric; belts are unrelated.
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A driver reports a coach's windshield fogs from the inside and there is a sweet smell in the cab; the coolant level is dropping. What is the diagnosis?
- Worn wiper blades.
- A leaking heater core.
- A leaking A/C evaporator.
- A plugged cab filter.
Show the answer
B. Correct. Coolant escaping from the heater core inside the HVAC box is vaporized by the blower and deposited on the glass as a film that fogs, with the sweet glycol smell, while the coolant level falls with no external leak. The RSOS lists steaming windshield and coolant smell among heating symptoms and heater cores among components replaced; the core is pressure-tested, replaced, the box cleaned, and the system refilled and bled. Coolant is a listed hazard (hot coolant) and a toxic material to handle and dispose of properly.
Why not the others
A. Wipers act on the outside of the glass; the fogging and smell are inside.
C. An evaporator leak loses refrigerant, which does not smell sweet or drop the coolant level.
D. A plugged filter reduces flow; it does not fog the glass with a sweet smell or use coolant.
02Answer key
| Question | Answer | Sub-task |
|---|---|---|
| Q1 | B | Diagnoses air conditioning systems |
| Q2 | B | Diagnoses heating and ventilation systems |
| Q3 | D | Diagnoses air conditioning systems |
| Q4 | C | Diagnoses heating and ventilation systems |
| Q5 | B | Diagnoses heating and ventilation systems |
03What block I covers
This block covers cab heating, ventilation and air conditioning on trucks and coaches. It includes heater cores, coolant flow valves, blowers and speed resistors, blend door actuators, auxiliary heaters, R-134a and R-1234yf refrigerants, compressors and clutches, condensers and expansion valves, A/C gauge diagnosis, nitrogen leak testing, recovery and recharging, and refrigerant handling certification.
The Red Seal Occupational Standard names this block “Services, diagnoses and repairs climate control systems”. It carries 5.2% of the exam, about 7 of the 135 questions, split across two tasks. The share column is each task's weight within the block, as the standard publishes it.
| Task and its sub-tasks | Share of block |
|---|---|
| Services, diagnoses and repairs heating and ventilation systems Services heating and ventilation systems; Diagnoses heating and ventilation systems; Repairs heating and ventilation systems | 46% |
| Services, diagnoses and repairs air conditioning systems Services air conditioning systems; Diagnoses air conditioning systems; Repairs air conditioning systems | 54% |
04What the questions turn on
Hose temperatures show flow
Lukewarm cab heat with a hot heater inlet hose and a much cooler outlet hose means little coolant is passing through the core. Check the flow valve for full travel, then flush or replace a restricted heater core.
Identify the refrigerant first
On a system with an unknown history, connect a refrigerant identifier before any recovery or charging. A mixed or wrong refrigerant contaminates the recovery machine, and R-1234yf is mildly flammable. A contaminated charge goes into a dedicated tank.
Reading A/C pressures
High pressure on both sides points to poor condenser heat rejection, such as a condenser packed with debris or a fan not pulling air. Frost at the expansion valve, a warm suction line and a low low side mean a low charge or a restriction.
Leak testing with nitrogen
When a detector cannot find a slow leak, recover the refrigerant and pressurize the system with dry nitrogen; a pressure drop confirms the leak. Charging with refrigerant just to leak-test is prohibited. Nitrogen also flows through a line while it is brazed.
05The other blocks
The 310T exam has 11 blocks. Each has its own page of free questions:
The 310T Truck and Coach Technician practice exam page describes the full question bank. How these questions are written and checked: how our questions are made. Found a mistake? Tell us and we will fix it.