Heating, Ventilation and Air Conditioning (HVAC) Flashcards

The blend door (air mix door) in an HVAC system is primarily responsible for:

Answer: Controlling the ratio of heated and cooled air to regulate cabin temperature

The blend door mixes air flowing over the heater core with air bypassing it to achieve the precise cabin temperature set by the driver.

What is the recommended service interval for replacing the cabin air filter on most vehicles?

Answer: Every 15,000–25,000 km or annually

Most manufacturers recommend replacing the cabin air filter every 15,000–25,000 km or annually to maintain proper HVAC airflow and filter effectiveness.

Which vehicle system does the heater core draw its heat energy from?

Answer: The engine cooling system

The heater core is plumbed into the engine cooling system; hot coolant flows through it and cabin air passes over its fins to provide passenger compartment heat.

A customer reports no heat despite the engine reaching normal operating temperature. Coolant level is correct. What should the technician check NEXT?

Answer: Heater core coolant flow and blend door actuator function

If the engine is at normal temperature and coolant level is correct, restricted heater core flow or a failed blend door actuator is most likely preventing heat delivery to the cabin.

What does selecting recirculation (MAX A/C) mode accomplish in an HVAC system?

Answer: Closes the fresh air inlet and recirculates air already inside the cabin

Recirculation mode closes the outside air intake so the A/C system cools already-conditioned cabin air, achieving maximum cooling efficiency on hot days.

A musty odour from the HVAC vents when the A/C is first turned on is typically caused by:

Answer: Mould or bacterial growth on the evaporator core surface

Condensation on the evaporator core creates a persistently moist environment where mould and bacteria thrive, producing musty odours when the system first operates.

Which refrigerant with a very low Global Warming Potential (GWP below 1) is replacing R-134a in newer vehicles under updated environmental regulations?

Answer: R-1234yf

R-1234yf has a GWP of less than 1 compared to R-134a's GWP of 1,430, making it the preferred refrigerant in new vehicles under current North American and European environmental regulations.