MLR: HVAC

Technician A says the job of the cooling system is to  remove heat that is absorbed by the engine. Technician B says the job of the cooling system is to warm up the engine quickly. Who is correct?

• A only

• B only

• Both

• Neither

Answer explanation

Technician A is correct that the cooling system removes heat from the engine, while Technician B is also correct as it helps warm up the engine quickly during startup. Therefore, both statements are valid.

At what temperature does an engine run cleanest with least wear?

• 100

• 150

• 180

• 200

Answer explanation

An engine runs cleanest and experiences the least wear at higher temperatures due to better combustion efficiency and reduced oil contamination. Therefore, 200°F is optimal for performance and longevity.

A cooling system with a 17 psi radiator cap will have what boiling point?

• 212

• 229

• 263

• 272

Answer explanation

A 17 psi radiator cap raises the boiling point of water. The boiling point increases by about 3 degrees Fahrenheit for every additional psi. Thus, 17 psi raises the boiling point to approximately 263°F.

How is the Air Delivery temperature controlled during A/C operation?

• By controlling how much air passes over the heater core

• By controlling the amount of Recirculation air

• By controlling the amount of air that passes through the radiator

• By controlling the amount of opening in the Heater Control Valve  

Answer explanation

The Air Delivery temperature is controlled by regulating how much air passes over the heater core. This directly affects the temperature of the air being delivered into the cabin, making it the correct choice.

Technician A says that to cover all possible vehicle conditions, the coolant must have a low freezing point. Technician B says coolant must have a high boiling point. Who is correct?

• A only

• B only

• Both

• Neither

Answer explanation

Both technicians are correct. A low freezing point prevents coolant from freezing in cold conditions, while a high boiling point prevents it from boiling over in hot conditions, ensuring optimal performance in all vehicle conditions.

When a thermostat is closed, where does the coolant from the engine go?

• To the heater core

• To the water pump

• To the radiator

• To the heater control valve

Answer explanation

When the thermostat is closed, it prevents coolant from flowing to the radiator. Instead, the coolant circulates back to the water pump, allowing the engine to reach its optimal operating temperature.

The air delivery subsystem of the HVAC system does all of the following EXCEPT:

• Ionize the air

• Clean the air

• Dehumidify the air

• Cool the air

Answer explanation

The air delivery subsystem of an HVAC system is responsible for cleaning, dehumidifying, and cooling the air. However, it does not ionize the air, making 'Ionize the air' the correct answer as the exception.

Which of these is NOT a type of HVAC control head?

• Electronic

• Manual

• Vacuum

• Pneumatic

Answer explanation

Pneumatic is not a type of HVAC control head. The main types are Electronic, Manual, and Vacuum. Pneumatic systems use air pressure for control, but they are not classified as a control head type.

Technician A says HVAC systems have 3 subsystems. Technician B says HVAC systems all work off of the same basic principles. Who is correct?

• A only

• B only

• Both

• Neither

Answer explanation

Technician A is correct that HVAC systems have 3 subsystems, typically including heating, ventilation, and air conditioning. Technician B is also correct as all HVAC systems operate on the same basic principles of thermodynamics and fluid mechanics. Thus, both are correct.

Which of the following systems is the least 'variable'?

• VDTXV

• CCTXV

• VDOT

• CCOT

Answer explanation

CCOT is the least 'variable' system as it represents a constant control output, minimizing fluctuations compared to the other options, which involve varying degrees of control and feedback.