HVAC & Emissions — Auto Service Technician (310S) Practice Questions

Free HVAC & Emissions practice questions

1. 1.The A/C refrigerant used in most modern vehicles is:

   • A.R12 (Freon)
   • B.R-134a or R-1234yf✓
   • C.R22
   • D.CO₂

   Why: R-134a is being phased out for R-1234yf (lower global warming potential). R-12 was banned (ozone depletion). Systems are NOT interchangeable — wrong refrigerant damages the system.

2. 2.The EVAP system prevents:

   • A.Engine overheating
   • B.Fuel vapour from escaping to the atmosphere — capturing and purging them through the engine✓
   • C.Oil leaks
   • D.Coolant loss

   Why: EVAP: fuel tank vapors stored in a charcoal canister, then purged into the intake manifold for combustion. P0440, P0442, P0455 = EVAP leaks (often a loose gas cap).

3. 3.The heater core provides cabin heat by:

   • A.Electric heating only
   • B.Circulating hot engine coolant through a small radiator inside the HVAC housing✓
   • C.Burning fuel
   • D.Exhaust heat

   Why: Hot coolant from the engine flows through the heater core. The blower fan pushes cabin air across the core, transferring heat. A blend door controls the mix of hot/cold air.

4. 4.NOx emissions increase when:

   • A.Engine is cold
   • B.Combustion temperatures are high (lean mixtures, high load, advanced timing)✓
   • C.Engine is rich
   • D.Engine is off

   Why: NOx forms above ~2500°F. Conditions: lean mixture, advanced timing, high cylinder pressure, carbon buildup. EGR reduces NOx by lowering peak combustion temperature.

5. 5.A two-stage catalytic converter contains:

   • A.Only reduction catalyst
   • B.Both reduction catalyst (NOx→N₂) and oxidation catalyst (CO/HC→CO₂/H₂O)✓
   • C.Only oxidation catalyst
   • D.No catalysts

   Why: Three-way cat: reduction bed removes NOx, oxidation bed removes CO and HC. Requires stoichiometric AFR (14.7:1) for maximum efficiency of both reactions.

6. 6.The secondary air injection system reduces emissions during:

   • A.Highway driving
   • B.Cold starts by injecting fresh air into the exhaust to help the catalytic converter reach operating temperature faster✓
   • C.Hot operation
   • D.Only at idle

   Why: Cold catalyst doesn't convert emissions. Secondary air + hot exhaust = exothermic reaction at the catalyst, heating it to operating temperature faster (light-off). Reduces cold-start emissions.

7. 7.An emissions readiness monitor that shows 'Not Ready' means:

   • A.The system passed
   • B.That specific self-test hasn't completed its drive cycle yet✓
   • C.The system failed
   • D.The car is broken

   Why: 'Not Ready' = the monitor hasn't run yet. Requires specific driving conditions (speed, temp, load patterns). Most jurisdictions allow 1-2 incomplete monitors for emissions testing.

8. 8.A/C compressor clutch not engaging — first check:

   • A.Replace compressor
   • B.Refrigerant charge, electrical connector, fuse, and relay before condemning the compressor✓
   • C.Replace the clutch
   • D.Replace the condenser

   Why: Most common: low refrigerant (low-pressure switch open). Also check: fuse, relay, clutch gap, connector, and PCM command. Compressor replacement is last resort.

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