Question 1

The blower motor does not run in any fan switch position. A check with a DMM reveals that power is getting to the motor. Technician A says the motor ground is bad. Technician B says the motor is burned out. Who is correct?

Accepted Answer

Both Technician A and Technician B could be correct. If power is getting to the motor but it's not running, a bad ground could prevent the circuit from completing, which is what Technician A suggests. On the other hand, if the motor itself is burned out as Technician B suggests, it wouldn't run even if power is supplied and the ground is good.

Question 2

Airflow control valves in the ventilation duct work are operated by ______.

Accepted Answer

Airflow control valves in ventilation ductwork can be operated by electric motors, vacuum motors, or cables, making all the provided options correct.

Question 3

Technician A says an A/C system using CO₂ [carbon dioxide] for a refrigerant will not contribute to global warming and is environmentally friendly. Technician B says CO₂ refrigerant does not need to be recovered and recycled. Who is correct?

Accepted Answer

The answer of Technician A says an A/C system using...

Question 4

The boiling point of a liquid increases as ______.

Accepted Answer

With increased pressure, the boiling point of a liquid also increases. This is because higher pressure compresses the vapor phase of the liquid, making it more difficult for molecules to escape and evaporate. As a result, more thermal energy is needed to reach the boiling point and convert the liquid to its gaseous state. Conversely, decreasing the pressure would lower the boiling point since it reduces the vapor pressure and allows molecules to escape more easily. Changes in surface area do not affect the boiling point since it only impacts the rate of evaporation, not the temperature required for boiling.

Question 5

Technician A repairs a leaking heater core. Technician B replaces it with a new core. Who is correct?

Accepted Answer

The answer of Technician A repairs a leaking heater core....

Question 6

Technician A says hybrid vehicles have an electric water pump to circulate coolant through the heater core when the engine is stopped. Technician B says hybrid vehicles have a hot coolant storage tank to provide heat for the passenger compartment when the engine is shut down. Who is correct?

Accepted Answer

Both statements are correct. Hybrid vehicles often use electric water pumps to circulate coolant for cabin heating when the engine is off, and many also have a hot coolant storage tank to maintain heat for the passenger compartment without running the engine.

Question 7

Heater cores with electric PTC heater strips are used on what type of vehicle?

Accepted Answer

Hybrid vehicles often use heater cores with electric PTC (Positive Temperature Coefficient) heater strips to provide supplemental cabin heating, especially when the engine is not running frequently or at all, as in electric-only mode.

Question 8

A vehicle with insufficient heater performance is being discussed. Technician A says the problem could be a stuck-open engine thermostat. Technician B says air could be trapped inside the heater core. Who is correct?

Accepted Answer

Both Technician A and Technician B are correct. A stuck-open engine thermostat can prevent the engine from reaching its optimal operating temperature, which can result in poor heater performance. Additionally, air trapped inside the heater core can prevent hot coolant from circulating through the heater core, resulting in reduced heat output from the heater.

Question 9

A subcooler is located ______.

Accepted Answer

A subcooler is typically located at the bottom of the condenser in refrigeration and air conditioning systems. It cools the liquid refrigerant below its condensation temperature to increase the efficiency of the system. Choices A, B, and D do not accurately describe the location of a subcooler in such systems.

Question 10

Technician A says the compressor can pump both liquids and vapor. Technician B says the compressor is driven off the crankshaft by a belt. Who is correct?

Accepted Answer

The answer of Technician A says the compressor can pump...

Question 11

Variable displacement compressors are normally _____ compressors with a pivoting wobble plate.

Accepted Answer

Variable displacement compressors that use a pivoting wobble plate are typically axial compressors. This design allows for the adjustment of the compressor's displacement, making it more efficient by varying the output based on the cooling demand.

Question 12

The refrigerant is at its lowest pressure and temperature at the ______.

Accepted Answer

The refrigerant is at its lowest pressure and temperature at the evaporator orifice (inlet) where it is expanding from a high pressure and temperature liquid to a low pressure and temperature vapor.

Question 13

Before 1994, most manufacturers used _____ as a refrigerant.

Accepted Answer

Before 1994, most manufacturers used R-12 as a refrigerant.

Question 14

Which of these statements is true?

Accepted Answer

The answer of Which of these statements is true?
...

Question 15

Technician A says European and Japanese manufacturers shipping vehicles to the US will eliminate R-134a A/C systems by 2017. Technician B says the United States will switch to R-22 in 2015. Who is correct?

Accepted Answer

The answer of Technician A says European and Japanese manufacturers...

Question 16

Technician A says hybrid vehicles use electrically driven high voltage A/C compressors. Technician B says the compressors for hybrids use the same refrigerant oil as regular vehicles. Who is correct?

Accepted Answer

Technician A is correct because hybrid vehicles often use electrically driven high voltage A/C compressors to allow the air conditioning system to operate without the internal combustion engine running. Technician B is incorrect because the compressors for hybrids typically require a special type of refrigerant oil that is non-conductive to prevent electrical issues, unlike the oil used in regular vehicle A/C systems.

Question 17

Technician A says a hybrid vehicle has a large reservoir of liquid refrigerant to keep the passenger compartment cool during long periods when the engine is shut down. Technician B says some hybrid vehicles have electrically driven A/C compressors. Who is correct?

Accepted Answer

Technician B is correct. Hybrid vehicles may not have a large reservoir of liquid refrigerant to keep the passenger compartment cool during long periods when the engine is shut down. Instead, some have electrically driven A/C compressors that can keep the cabin cool without the engine running. Technician A is incorrect because their statement is not necessarily true for all hybrid vehicles.

Question 18

Technician A says in most cases, problems with the heating system are problems with the engine's cooling system. Technician B says a restricted heater return hose can cause excess heat in the passenger compartment. Who is correct?

Accepted Answer

Technician A is correct because the heating system in a vehicle typically relies on the engine's cooling system to function properly. If there's an issue with the cooling system, it can affect the heating system. Technician B is incorrect because a restricted heater return hose would likely cause insufficient heating in the passenger compartment, not excess heat.

Question 19

If little or no resistance is felt while operating the temperature control lever, the problem is most likely which of the following?

Accepted Answer

The lack of resistance when operating the temperature control lever typically indicates a mechanical disconnect or slippage, such as the control cables having slipped loose from the dash control or door arm. This prevents the lever from properly actuating the mechanism it controls.

Question 20

Technician A says the magnetic clutch is usually pressure controlled, cycling the compressor on and off to regulate system temperature or pressure. Technician B says the clutch operates continually when the system is turned on. Who is correct?

Accepted Answer

The answer of Technician A says the magnetic clutch is...

Quiz 54: Heating and Air Conditioning