HVAC

Question 1

What two components in the HVAC system are used as heat exchangers?

Answer 1

The heater core and the evaporator.

Question 2

How does dehumidifying work in the HVAC system?

Answer 2

As the air passes the evaporator, it is cooled and the water in the air condenses and adheres to the evaporator fins.

Question 3

How is temperature controlled in a HVAC system?

Answer 3

An air mix damper is used, which progressively either allows or stops airflow through the heater core.

Question 4

How does natural flow-through ventilation work?

Answer 4

Air pressure is generated by the vehicle’s forward movement, and intake and exhaust vents are placed in the car to allow air flow.

Question 5

What is the purpose of the cabin filter?

Answer 5

It is used to purify the air that is drawn in from outside the car.

Question 6

What does the air inlet damper do?

Answer 6

Switches between fresh and recirculated air.

Question 7

What does the air flow damper do?

Answer 7

Directs whether air goes to feet, face, or windscreen.

Question 8

What ways can a damper be controlled?

Answer 8

Through wire cables, or with a motor.

Question 9

How does a resistor type blower work?

Answer 9

It uses a number of resistors in series, and the lowest speed will use all the resistors, and the highest speed will use no resistors.

Question 10

How does a transistor type blower work?

Answer 10

It uses a transistor which has a control of many resistances on the one resistor.

Question 11

What type of refrigerant does Toyota use?

Answer 11

R134a

Question 12

What does refrigerant do to heat when condensing / evaporating?

Answer 12

Removes heat when evaporating and releases heat when condensing.

Question 13

What three characteristics does refrigerant need to be used in vehicles?

Answer 13

Evaporate / condense easily, be safe to handle, and be stable and maintain quality.

Question 14

What in relation to boiling point is a beneficial characteristic of refrigerant.

Answer 14

At low pressure, refrigerant evaporates at a low temperature, and at high pressure it has a high boiling point.

Question 15

What are the main components of the refrigerant system?

Answer 15

Compressor, condenser, receiver/dryer, expansion valve, and evaporator.

Question 16

What is the flow of refrigerant in the HVAC system?

Answer 16

Compressor releases high press/high temp gas -> gas flows to condenser, gas condenses to liquid (releases heat to outside air) -> liquid flows to receiver/dryer, stores/filters liquid -> filtered liquid flows to expansion valve which releases liquid/gaseous mixture to evaporator -> the refrigerant is at a much reduced pressure (boiling point lower) so it evaporates and draws in heat energy -> gas is drawn to compressor.

Question 17

What is conduction?

Answer 17

The transmission of heat within a substance.

Question 18

What is convection?

Answer 18

When heat is applied to a container of liquid or gas, the substance at the bottom rises to the top, as the substance is pushed to the top, the substance that was at the top is lowered to the bottom, and then also heated.

Question 19

What is radiation?

Answer 19

The emission and transfer of heat in the form of infrared rays.

Question 20

What is the difference between latent heat and sensible heat?

Answer 20

Sensible heat changes the temperature of an object, latent heat changes the state of an object without changing the temperature.

Question 21

What is absolute pressure?

Answer 21

The pressure in relation to a perfect vacuum, or 0kPa.

Question 22

What is gauge pressure?

Answer 22

Gauge pressure is 14.6psi (atmospheric pressure), and is what most gauge call 0psi.

Question 23

What are the common types of AC compressors used in Toyotas?

Answer 23

Scroll, swash plate, variable swash plate, and electric.

Question 24

How does an AC pulley work?

Answer 24

There is a stator in the pulley, which when current is sent through it, magnetises. This then draws the pulley’s centrepiece into the compressor shaft and spins the compresser.

Question 25

What does the receiver / dryer do?

Answer 25

It stores liquid refrigerant from the condenser and eliminates any moisture or foreign matter through a desiccant and strainer.

Question 26

What does a thermal expansion valve (TX) do?

Answer 26

It uses a needle valve which is attached to a heat sensing rod to put through different amounts of refrigerant to the evaporator depending on cooling loads put on the evaporator.

Question 27

What does the pressure switch do in the HVAC system?

Answer 27

It monitors refrigerant pressure and will turn off the magnetic clutch if it senses abnormal pressure.

Question 28

What does the evaporator temperature control do?

Answer 28

It senses temperature of the surface of the evaporator, if temperature starts to get close to 0 degrees, it will turn of the magnetic clutch of the compressor.

Question 29

What does the idle-up control do?

Answer 29

At idle, the AC ECU will send a signal to the engine ECU and that will open up the idle speed control valve a bit to allow for the extra load.

Question 30

What does the compressor two-stage control system do?

Answer 30

If the AC switch is on, the evaporator temp sensor will turn the magnetic clutch off at 3 degrees and turn it back on at 4 degrees. In ECON mode, it will turn the magnetic clutch off at 10 degrees and turn it back on at 11 degrees.

Question 31

What are the 14 components associated with the automatic AC system?

Answer 31

AC control ECU, engine ECU, control panel, interior temp sensor, ambient temp sensor, solar sensor, evap temp sensor, water temp sensor, AC press. switch, air mix servomotor, air inlet servomotor, air flow servomotor, blower motor, and the blower controller.