Automotive HVAC 1 Quiz 1

Most systems use a flap door that swings about __ degrees.

45 to 90

Humans prefer relative humidity that is between:

45% to 55%

What section of the clean air act concerns work on air conditioning systems in vehicles?

609

Humans prefer temperatures that are between:

68F to 78F

How can a refrigerant cause the breakup or depletion of the ozone layer?

A chlorine atom from a chlorinated fluorocarbon (CFC) such as R-12 can travel into the stratosphere if it escapes or is released. There, under the effects of ice clouds and sunlight, it can combine with one of the oxygen atoms of an ozone molecule to form chlorine monoxide and an ordinary oxygen molecule, O2. This destroys that ozone molecule. The chlorine can then break away and attack other ozone molecules.

What is the difference between a pressure switch and a pressure sensor?

A pressure switch is either on or off, whereas a pressure sensor is variable and supplies pressure information to the PCM/BCM.

What is a "reheat" system.

A system that cools the air through the evaporator then heats the air through airflow through the heater core.

Orifice Tube System

Accumulator on the low (vapor) side.

What are the advantages and disadvantages of a thermal expansion valve system?

Advantages: 1) The TXV can maintain a low superheat to ensure that the majority of the evaporator surface is being used, resulting in higher efficiency. 2) Requires a smaller refrigerant charge. Disadvantages: 1) The system costs more to produce. 2) There are more moving parts.

Where does the air enter the vehicle when outside air is selected?

Air enters the duct system from the plenum chamber in front of the vehicle's windshield (outside air).

What do the three main HVAC doors do?

Air inlet door is used to select outside or inside air inlet. Temperature-blend door is used to adjust air temperature. Mode door is used to select air discharge location.

Temperature-blend door is also called:

Air-mix door, temperature door, blend door, diverter door, and bypass door.

How does an electromagnetic compressor clutch work?

Allows the compressor to be turned on and off. The clutch uses a coil of wire where a magnetic field is generated when electrical current flows through it. The magnetic field pulls the drive plate against the rotating pulley to drive the compressor.

Thermodynamics Third Law

As a system approaches absolute zero, the entropy of the system approaches a minimum value.

The letter "a" in R-134a means:

Asymmetrical

Heat intensity is measured in:

BTUs

Bi-level Setting

Both in-dash and floor discharge.

The refrigerant is circulated through the system by a:

Compressor

What are the major components of the refrigeration cycle?

Compressor, condenser, expansion device, evaporator.

In a piston-type compressor, the pistons are driven by a:

Crankshaft, swash plate, or a wobble plate.

Pressures are controlled in an orifice tube (OT) system by:

Cycling an electromagnetic compressor clutch on and off as needed or using a variable displacement compressor.

What type of refrigerant oil is used in R-134a systems?

Either POE (polyalkylene glycol) or PAG (poly ester) depending on the vehicle.

Thermodynamics First Law

Energy cannot be created or destroyed, but can change form and location.

Thermodynamics Second Law

Energy must flow from a higher state to a lower state.

When the refrigerant evaporates, it absorbs heat when it changes from a liquid to a gas. In which unit does this occur?

Evaporator

Heat Setting

Floor level with outside air inlet.

Max Heat Setting

Floor level with recirculation.

"Outside air" is also called __ air.

Fresh

The air inlet control door is also called __.

Fresh air door, recirculation door, or outside air door.

How does heat move?

Heat can travel through one or more of three paths as it moves from hot to cold: 1) Conduction 2) Convection 3) Radiation

How does the refrigeration system work?

High-pressure liquid refrigerant flows through an expansion device, which controls the amount of refrigerant that is allowed to pass through. When the high-pressure liquid passes through the expansion device, the pressure drops. This causes the liquid refrigerant to evaporate in a small radiator-type unit, called the evaporator. When the refrigerant evaporates, it absorbs heat when changing from a liquid to a gas. As the heat is absorbed by the refrigerant, the evaporator becomes cold. After the refrigerant has evaporated into a low-pressure gas in the evaporator, it flows into the engine-driven compressor. The compressor compresses the low pressure refrigerant gas into a high-temperature, high pressure gas and forces it through the system. The high-pressure gas flows into the condenser located in front of the cooling system radiator. The condenser looks like another radiator, and its purpose and function is to remove heat from the high-pressure gas. In the condenser, the high-pressure gas changes (condenses) to form a high-pressure liquid as the heat from the refrigerant is released to the air. The high-pressure liquid then flows to the expansion device, which controls the amount of refrigerant that is allowed to pass through and meters the flow into the evaporator. When the high pressure of the liquid passes through the expansion device, the pressure drops and causes the refrigerant to vaporize, starting the cycle all over again.

Heat travels from:

Hot to cooler.

Where is the air directed when the control panel is set to defog/defrost position?

In the defog or defrost mode position, the air is directed through the evaporator to remove the moisture from the air before being sent through the heater core to warm the air.

How does a coaxial swash-plate compressor work?

It drives the pistons through a swash plate, which is attached to the driveshaft. The swash plate is mounted at an angle so it will wobble and cause the reciprocating action of the pistons.

The low side of the refrigeration cycle means:

It has low temperature and pressure.

R-134a is in what color container?

Light blue.

Switches located on the compressor itself may include a:

Low-pressure switch, high-pressure switch, or low- and/or high-pressure sensor.

The lower the GWP number, the:

Lower the global warming potential.

The __ door is used to select air discharge location such as floor, vent, or defrost.

Mode

How does a "reheat" system work and why?

Most HVAC systems are considered reheat systems in that the incoming air is chilled as it passes through the evaporator. The air is then heated as part or all of the flow passes through the heater core so it reaches the desired in-vehicle temperature.

How does the air conditioning cool the inside of the vehicle?

Move heat from inside to outside of the vehicle. Heat travels from a higher temperature to a lower temperature.

An air-conditioning system cools the interior of the vehicle by:

Moving the heat from inside the vehicle to outside the vehicle.

What components are often included as part of a cooling module?

On most vehicles, the condenser is part of a cooling module that can combine the following: - Condenser - Radiator - Automatic transmission fluid cooler - Power steering pump oil coolers - An intercooler for engine intake air on turbocharged engines

How is the air gap of a compressor clutch adjusted?

On some compressors, install the adjusting shims onto the shaft, install the drive key, and align and install the hub.

What type of compressors are used in air conditioning systems?

Piston compressors, vane compressors, and scroll compressors.

The basic designs of AC compressors include:

Piston, vane, and scroll.

A compressor speed (belt lock) sensor is used by the HVAC ECM to:

Prevent a locked-up compressor from destroying the engine drive belt and determine if the compressor is running by comparing the compressor and engine speed signals.

In the heating mode, why is heat directed toward the floor?

Proper temperature control to enhance passenger comfort during heating should maintain an air temperature in the footwell about 7 to 14 degrees Fahrenheit above the temperature around the upper body.

What do the colors of the containers mean?

R-12 - White R-22 - Green R-134a - Light blue R-1234YF - White with a red stripe

Which refrigerant has the lowest global warming potential (GWP)?

R-744

Heat transferred through the air is called:

Radiation

TXV System

Receiver-drier located on the high (liquid) side.

How is relative humidity measured?

Relative humidity is commonly measured with a hygrometer or a psychrometer.

What is true about a SNAP refrigerant?

Requires unique set of fittings, and all ports not converted must be permanently disabled, each refrigerant must have a label with a unique color that specifies pertinent information, and all original refrigerants must be removed before charging with the new refrigerant.

What does the clean air act mandate when it comes to servicing air conditioning systems?

Section 609. Technicians who repair or service automotive A/C systems shall be properly trained and certified and use approved refrigerant recovery and recycling equipment.

Transducer

Senses pressure and changes a variable pressure signal into a variable electrical signal.

What is the difference between a switch and a sensor?

Sensors are thermistors and transducers and these provide a variable output instead of being on or off like a switch.

The three different states of matter include:

Solid, liquid, and gas.

What are the three states of matter?

Solid, liquid, and vapor (gas).

What is the difference between heat and temperature?

Temperature is the measure of the level of energy and is measured in degrees, whereas heat expresses the amount of heat needed to raise the temperature of one gram of water one degree Celsius. Heat is measured in British Thermal Units (BTU).

Air from the plenum can flow into one or two of three outlet paths:

The A/C registers (vents) in the face of the instrument panel, the defroster registers at the base of the windshield, or the heater outlets at the floor under the instrument panel.

What is the difference between an accumulator and a receiver-drier?

The accumulator is used with orifice tube systems and serves three major functions. 1) Prevents liquid refrigerant from passing to the compressor. 2) Holds the desiccant, which helps remove moisture from the system. 3) Holds a reserve of refrigerant. The receiver-drier is used with TXV systems and is normally found in the high-side liquid line, somewhere between the condenser and the TXV. It contains a filter and a desiccant just as the accumulator.

The ram air that enters the vehicle from the outside enters the HVAC system from __.

The base of the windshield.

How is the A/C compressor lubricated in an R-134a system?

The oil moves through the system simply with the movement of the refrigerant.

Why is it important to keep refrigerant oil containers closed?

To prevent the oil from absorbing moisture from the air.

What does the snowflake button on the dash do?

Turns on the AC compressor.

Most recent HVAC actuators are recalibrated after replacement by __.

Using a scan tool or allow it to self-learn after being installed.

What precautions are necessary when working with refrigerants?

Wear safety goggles or a clear face shield and protective clothing (gloves) when working with refrigerants. Always be in a well-ventilated shop area when working with refrigerants and avoid small, enclosed areas.

Defrost Setting

Windshield registers.

Is it possible for heat to be added to water without causing the temperature to increase?

Yes, it requires heat to transform a substance from one state to another. This added heat does not result in an increase in temperature.

A five-wire actuator uses two wires to power the motor (power and ground) and three wires for __.

A feedback potentiometer.

A stretch-type A/C compressor belt is removed using:

A knife (cut it).

Where is the ozone layer?

In the stratosphere.

A/C Setting

In-dash registers with outside air inlet.

Max A/C setting

In-dash registers with recirculation.

What is the difference between a vane compressor and a radial compressor?

Radial compressors use two double pistons that are mounted over a bearing block. The crankshaft moves the bearing block in a circular orbit that moves the pistons through their strokes. The vanes of a vane-type compressor are mounted in a rotor that runs inside a round, eccentric, or a somewhat elliptical, chamber. The vanes slide in and out of the rotor as their outer end follows the shape of the chamber. Compressors with a round, eccentric chamber have one pumping action per vane per revolution.

A cooling module usually includes what components?

Radiator, automatic transmission fluid cooler, and AC condenser.

Which unit contains a desiccant to remove moisture from the system?

Receiver-drier and accumulator.

Most piston compressors use what type of valves?

Reed

Air-conditioning process works through a fluid, called a __ that continuously changes state from liquid to gas and back to liquid.

Refrigerant

Precautions when working with refrigerants include:

Safety goggles or a clear face shield, well-ventilated shop area, and refrigerant containers are filled with reserve room left for expansion and the containers are marked with their critical temperatures.

Thermistor

Temperature sensor.

The door used to control interior temperature is called the __ door.

Temperature-blend