Nate Core exam

What makes a contract legal?

Any verbal or written agreement.

How do you find absolute pressure?

Gauge pressure + 14.7PSI

A vacuum gauge reads pressure in what?

Microns.

What are some characteristics of a dial stem thermometer?

Not quite as accurate as the glass stem thermometer, but it is low cost and durable.

Describe the manifold gauge set.

On the right = High pressure (Liquid) (discharge gauge) (Red) On the left = Compound or suction gauge (Blue) (Vapor)

What is used to remove refrigerant from a system properly?

Recovery machines.

What is used to weigh-in a refrigerant charge properly and also to record refrigerant removed for proper record keeping under the EPA rules?

Scales.

What can be used to calculate the relative humidity, dew point, and other properties of the air?

The difference between the wet-bulb and the dry-bulb temperature.

The size of a micron is?

1/1,000 mm (0.001 mm)

What is the proper distance from the wall equal to of the working length of the ladder?

1/4 (ex. if the ladder is 16 ft, the base should be 4 ft from the wall.)

What maximum temperatures are refrigerant cylinders able to hold quantities of refrigerant at definite maximum pressures?

125 Degrees Fahrenheit.

At what temperature will the liquid refrigerant expand to fill the cylinder at 80% capacity by weight?

130 Degrees Fahrenheit.

Ice has a latent heat of fusion of?

144 Btu/lb

How many microns are in 1 in?

25,400 microns.

What is the pressure range of a standard compound gauge on a refrigeration manifold?

30 in. Hg to 350 psig

What does a pressure gauge use as the operating element?

A bourdon tube.

What happens at extremely high hydrostatic pressures?

A cylinder could burst.

What is a class B fire, and how should you put it out?

A fire that contains oil, grease, paint, varnish, or other chemicals. Using a smothering agent such as foam.

What is the purpose of a swaging tool?

A method of joining tubing without a fitting.

What is needed with the sling psychometer to measure temperatures?

A psychometric chart or slide rule.

What is the grid pattern of measurements with a velometer known as?

A traverse.

What can be used to cut capillary tubing?

A triangular file or a knife edge file.

What can be soft soldered or hard soldered?

A tubing joint..

What can be used to measure pressures at low levels?

An electronic vacuum gauge.

How do you obtain the specific heat of liquid water?

By dividing Btu by the amount of water (lbs) and then by the temperature change (Degrees Fahrenheit).

How can heat be produced?

By electric heating elements, heat pumps, or by the chemical reaction of combustion.

Explain the effects of relative humidity.

By increasing the humidity during the heating season, the evaporation of moisture is slowed, therefore you feel warmer and vice versa.

How do you calculate cubic feet per minute? (cfm)

By multiplying the velocity of air passing through a duct X the area of the duct.

How do you determine the cfm of air moving through the duct?

By taking the average velocity multiplied by the area of the duct.

All cylinders and other chemicals being transported in a service vehicle are regulated by?

DOT (Department of Transportation)

Before leaving a service call, you should be sure to?

Demonstrate system operation and describe basic maintenance procedures to the customer.

What is frequently used in HVACr applications to operate switches to prove airflow?

Diaphragm type gauges.

What is often used to measure pressure drop? (The difference in pressure between two points.)

Differential pressure gauges.

How do you remove noncondensables, air, and moisture from a system?

Drawing a deep vacuum with a vacuum pump.

What do the glass stem thermometer and the dial stem thermometer measure?

Dry-bulb temperature.

What temperature is in relation to human comfort?

Dry-bulb temperature.

What is a class C fire, and how should you put it out?

Electrical fire. Nonconducting agent such as carbon dioxide.

Many problems HVACr technicians face are?

Electrical problems.

What should you never do with a refrigerant cylinder?

Fill beyond 80% by weight. Fill a cylinder with refrigerant it is not rated/approved for.

What do aluminum pipe and fittings require?

Filler material specially designed for aluminum.

What are 4 hazardous atmospheres encountered in confined spaces?

Flammable, toxic, irritant, and or corrosive, and asphyxiating.

What does soft soldering requrie?

Flux.

What is needed to create combustion?

Fuel. Oxygen. Heat.

What is a GFCI?

Ground vault circuit interrupter. Disconnects load from power source when activated from an imbalance between the line current and the neutral current.

When drilling overhead you shoud wear?

Impact resistant goggles.

What pressure scales are used in pressure gauges?

Inches of water column. (in w.g.) and (PSI)

What are some different tools that measure differential pressure?

Inclined manometers. / U-tube manometers. / Handheld digital manometers. / Diaphragm type gauges.

What is the purpose of a flaring tool?

It allows you to join soft drawn copper tubing without the use of a coupling.

What can inhalation of refrigerant do?

It can cause dizziness. Nausea. Heart irregularities. Unconsciousness. Even death.

What does burring cause on the inside of tubing?

It can create turbulence and pressure drop inside the piping.

What can flux do to components and refrigeration system?

It can damage both.

What can a magnehelic gauge measure?

It can measure differential pressures in hundredths of an inch of water column pressure.

What is a sling psychometer?

It combines glass stem thermometers to measure both dry-bulb and wet-bulb temperatures.

How doea a fan powered humidifier operate?

It contains its own fan to move air through the humidifier.

Describe the glass stem thermometer.

It has a liquid filled tube marked off with a graduated temperature scale.

What can a dirty filter cause?

It increases static pressure which can decrease the quantity of air delivered by the fan and increase the motors current draw?

What is combustion?

It is a chemical process.

What is a class A fire, and how should you put it out?

It is an ordinary fire that is the burning of wood, paper, or textile products. Water.

What is the digital psychrometer able to do?

It is capable of reading dry-bulb and wet-bulb temperature and %RH.

What does A1 safety classification mean?

It means that the refrigerant is considered to be non-toxic and non-flammable.

What does conditioning the air mean?

It means that you are concerned with the temperature, humidity, filtration, and ventilation.

What does a balometer measure and how does it measure?

It measures airflow and cfm by capturing all of the air from a diffuser through the measuring portion of the unit.

What does a velometer measure and what is its purpose?

It measures velocity pressure and static pressure in order to determine the air velocity in a duct.

How does a bypass type humidifier operate?

It pushes air from the main blower through the humidifier to absorb moisture then discharges it back to the return duct.

How should a bypass type humidifiers damper be used?

It should be open during the heating season. It should be closed during the cooling season.

How should tubing be cut?

It should be scored all the way around the outside and then snapped to prevent closing of the inside diameter.

What is the purpose of the grid pattern known as a traverse?

It takes an average velocity through the duct to ensure an accurate airflow measurement.

What does an anemometer use and measure?

It uses a fanblade to measure the velocity of air and feet per minute.

What does potential energy convert to when in motion?

Kinetic energy.

When added to or removed from a substance, what energy will cause a change in state? (Not in temperature)

Latent heat.

What is the MSDS?

Material safety data sheet contains information regarding the proper use of the product relevant safety precautions, PPE, and emergency procedures.

What are 3 energy examples that can be stored?

Mechanical energy. / Chemical energy. / Electrical energy.

What measurement is used to measure a vacuum?

Microns.

When is flux required?

Only if copper is being joined to brass or steel.

Nealy half of all HVAC injuries are caused by?

Overexertion. Slips. Falls.

What is stored energy capable of doing work called?

Potential energy.

What is differential pressure?

Pressure drop across various system components.

What is housekeeping referred to as?

Proper storage of material and equipment. Regular clean-up of waste and debris. Fire prevention and protection.

What can be used to remove a burr on the inside of tubing?

Reamers and deburrers.

When talking to a customer what term should be used when referring to refrigerant?

Refrigerant. (NOT freon, gas, juice)

What can the dry-bulb and wet-bulb temperatures be used to determine?

Relative humidity (%RH) The dew points. Other properties of the air.

Before you charge a system with refrigerant or after you have replaced a component or repaired a leak, you should?

Remove all air and moisture from the system.

When added to or removed from a material, what heat energy will cause a change in temperature or that can be measured with a thermometer.

Sensible heat.

Which leak detection method is not as sensitive as the other methods?

Soap bubbles.

Different leak detection methods are?

Soap bubbles. Ultrasonic devices. Electronic leak detectors.

Spring-Type benders can only be used on what type of tubbing?

Soft drawn copper

What are the most common methods for joining copper tubing?

Soldering or brazing.

What are three phases of matter?

Solid. / Liquid. / Gas

What value do you get when you divide the amount of heat (Btu) by the amount of ice (lb) and then by the temperature change (Degrees Fahrenheit)?

Specific heat.

How does relative humidity affect evaportion?

The higher the relative humidity the more slowly moisture evaporates.

Why should oxygen never be pressurized into a refrigerant system?

The mixture of oxygen and the oil can create a violent explosion.

Why should hacksaws and power saws not be used when cutting tubing or refrigerant lines?

The small shavings created by the teeth of the saw can enter the tubing and do damage to the components of the system.

What can differential pressure gauges do?

They can calculate air flow. They can help you determine how clean or dirty a coil or filter is. Provides simultaneous pressure and flow measurements

Why should tube cutters be used?

They produce a square, clean cut and leave no shavings to contaminate the system.

What are pressure gauges used for?

To determine the static pressure in a duct system or the pressure drop across various system components. Such as blowers, filters, coils, and heat exchangers.

What can be used on soft drawn copper to provide a bend without kinking or damaging the tubing?

Tube benders.

When does an imbalance occur in a GFCI?

When the current travels through a ground path other than the neutral wire.

When is flux not required?

When you are brazing a copper-to-copper joint.

After flaring, swaging, and connecting the tubing, what do you do next?

You either solder or braze the connection.

What should be used when working with refrigerants during transfer, charging, repair operations, and when working with hydrochloric acid?

splash protective goggles. Face shields.