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Question 1Refrigeration Principles and System Components

In a vapor-compression refrigeration cycle, which component raises the pressure and temperature of the refrigerant vapor?

  1. Metering device
  2. Compressor Correct answer.
  3. Evaporator
  4. Condenser

Explanation

The compressor draws in low-pressure vapor and compresses it, raising both pressure and temperature so heat can be rejected in the condenser. The other components handle heat transfer or flow control, not compression.

Question 2Refrigeration Principles and System Components

The primary function of the condenser in a refrigeration system is to:

  1. Remove moisture from the refrigerant charge
  2. Reject refrigerant heat to the surroundings Correct answer.
  3. Reduce pressure before the evaporator
  4. Absorb heat from the conditioned space

Explanation

In the condenser, high-pressure refrigerant vapor gives up heat to the ambient air or water and condenses to a liquid. Heat absorption occurs in the evaporator, and pressure reduction occurs at the metering device.

Question 3Refrigeration Principles and System Components

Which refrigerant condition normally enters the compressor of a properly operating system?

  1. Low-pressure liquid refrigerant
  2. High-pressure liquid refrigerant
  3. Low-pressure superheated vapor Correct answer.
  4. High-pressure superheated vapor

Explanation

The compressor is designed to pump vapor, and the refrigerant should be superheated slightly before entering to ensure no liquid droplets are present. High-pressure vapor is the compressor discharge condition, not the suction condition.

Question 4Refrigeration Principles and System Components

The primary function of the metering device is to:

  1. Raise refrigerant pressure ahead of the condenser
  2. Meter flow and reduce pressure to the evaporator Correct answer.
  3. Filter debris from the suction line
  4. Remove moisture and acid from the system

Explanation

The metering device creates a pressure drop between the high side and low side and controls how much refrigerant enters the evaporator. Filtration and moisture removal are separate functions.

Question 5Refrigeration Principles and System Components

Latent heat is the heat that:

  1. Is released only by the condenser
  2. Changes a substance's state without changing temperature Correct answer.
  3. Is measured only in the suction line
  4. Raises the temperature of a substance without changing state

Explanation

Latent heat is associated with phase change, such as boiling or condensing, and occurs at constant temperature for a pure substance. Sensible heat, by contrast, changes the temperature of a substance.

Question 6Refrigeration Principles and System Components

Which line connects the evaporator outlet to the compressor inlet?

  1. Liquid line
  2. Suction line Correct answer.
  3. Discharge line
  4. Hot gas line

Explanation

The suction line carries low-pressure vapor from the evaporator back to the compressor. The liquid line feeds the metering device, and the discharge line carries high-pressure vapor away from the compressor.

Question 7Refrigeration Principles and System Components

A thermostatic expansion valve senses the temperature at the evaporator outlet with a:

  1. Remote bulb attached to the suction line Correct answer.
  2. Pressure gauge mounted on the liquid line
  3. Sight glass installed in the liquid line
  4. Thermocouple installed in the condenser

Explanation

The TXV's remote bulb is clamped to the suction line near the evaporator outlet and transmits pressure back to the valve to modulate refrigerant flow and maintain superheat. A sight glass and gauges are diagnostic tools, not the sensing element.

Question 8Refrigeration Principles and System Components

A filter drier is normally installed in which refrigerant line?

  1. Hot gas bypass line
  2. Liquid line Correct answer.
  3. Discharge line
  4. Suction line

Explanation

The filter drier is placed in the liquid line so it can remove moisture and debris before the refrigerant reaches the metering device. Suction line driers exist for cleanup, but the standard location is the liquid line.

Question 9Refrigeration Principles and System Components

The suction line temperature is 50°F and the evaporator saturation temperature is 40°F. What is the superheat?

  1. 40°F
  2. 50°F
  3. 10°F Correct answer.
  4. 90°F

Explanation

Superheat is the difference between the actual suction line temperature and the evaporator saturation temperature. Subtracting 40°F from 50°F gives 10°F of superheat.

Question 10Refrigeration Principles and System Components

Subcooling is calculated by:

  1. Subtracting suction line temperature from evaporating saturation temperature
  2. Subtracting liquid line temperature from condensing saturation temperature Correct answer.
  3. Subtracting suction pressure from discharge pressure
  4. Adding condensing and evaporating temperatures

Explanation

Subcooling is the number of degrees the liquid refrigerant is cooled below its condensing saturation temperature. It is found by subtracting the measured liquid line temperature from the condensing saturation temperature.

Question 11Refrigeration Principles and System Components

A TXV whose remote bulb has lost its charge will most likely:

  1. Throttle closed and starve the coil Correct answer.
  2. Maintain normal superheat
  3. Raise the condensing pressure significantly
  4. Open wide and flood the coil

Explanation

The bulb charge provides the opening force on the TXV. With no bulb charge, the closing spring dominates and the valve throttles closed, reducing refrigerant flow and causing high superheat.

Question 12Refrigeration Principles and System Components

The purpose of an accumulator in a refrigeration system is to:

  1. Store liquid refrigerant for system charging purposes
  2. Keep liquid refrigerant out of the compressor Correct answer.
  3. Remove moisture from the refrigerant
  4. Separate oil from refrigerant vapor

Explanation

An accumulator is installed on the suction line to trap any liquid refrigerant and allow it to boil off before vapor enters the compressor. This protects the compressor from slugging.

Question 13Refrigeration Principles and System Components

A receiver is typically located:

  1. At the compressor discharge
  2. Inside the evaporator coil
  3. Between evaporator and the compressor
  4. Between condenser and metering device Correct answer.

Explanation

The receiver stores liquid refrigerant after the condenser and supplies the metering device. It is a high-side component, not a suction-line or evaporator component.

Question 14Refrigeration Principles and System Components

Bubbles in a sight glass during normal steady operation most often indicate:

  1. Too much refrigerant oil in the crankcase
  2. Low charge or flash gas in the liquid line Correct answer.
  3. Normal operation under all load conditions
  4. A correct and full refrigerant charge

Explanation

A clear sight glass generally indicates a solid liquid seal, while bubbles suggest flash gas caused by low charge or a restriction. Bubbles can also appear during transient conditions, so they are interpreted at steady state.

Question 15Refrigeration Principles and System Components

Non-condensable gases such as air in a refrigeration system cause:

  1. Higher condensing pressure and discharge temperature Correct answer.
  2. Lower condensing temperature and lower liquid temperature
  3. Improved compressor efficiency and capacity
  4. Lower discharge pressure and lower suction pressure

Explanation

Non-condensables collect in the condenser and raise the condensing pressure beyond the saturation pressure of the refrigerant. This increases compressor work and discharge temperature.

Question 16Refrigeration Principles and System Components

Compression ratio is calculated by dividing:

  1. Suction pressure by discharge pressure
  2. Discharge temperature by suction temperature
  3. Absolute discharge pressure by absolute suction Correct answer.
  4. Condensing temperature by evaporating temperature

Explanation

Compression ratio uses absolute pressures, usually psia, with discharge pressure divided by suction pressure. Using gauge pressure or temperatures gives an incorrect ratio.

Question 17Refrigeration Principles and System Components

A crankcase heater is used to:

  1. Defrost the evaporator coil
  2. Superheat the suction gas entering the compressor
  3. Keep oil warm and limit refrigerant migration Correct answer.
  4. Raise the condensing pressure in cold weather

Explanation

The crankcase heater warms the oil so refrigerant that has migrated to the crankcase does not condense and dilute the lubricant. It does not directly heat suction gas or affect condenser pressure.

Question 18Refrigeration Principles and System Components

The primary purpose of refrigerant oil in a compressor is to:

  1. Lubricate parts and seal internal clearances Correct answer.
  2. Lower the refrigerant's boiling point
  3. Absorb moisture from the refrigerant
  4. Increase the system's refrigeration capacity

Explanation

Oil forms a lubricating film on bearings and moving surfaces and helps seal gaps between compressor parts. It is not a drying agent or a capacity-enhancing additive.

Question 19Refrigeration Principles and System Components

Which metering device is designed to maintain a relatively constant superheat over a wide range of loads?

  1. A fixed orifice
  2. A capillary tube
  3. A manual hand valve
  4. A thermostatic expansion valve Correct answer.

Explanation

A TXV modulates its opening in response to suction line temperature and pressure, so it adjusts flow to hold superheat near a set value. Capillary tubes and fixed orifices cannot adjust to load changes.

Question 20Refrigeration Principles and System Components

A capillary tube metering device is best suited for:

  1. Systems that require adjustable superheat
  2. Systems with a liquid receiver and TXV
  3. Small appliances with stable operating conditions Correct answer.
  4. Large industrial systems with widely varying loads

Explanation

Capillary tubes are low-cost, fixed-restriction devices matched to a specific system, making them suitable for small appliances with predictable loads. They do not adjust to load changes and are not normally used with a receiver.

Question 21Refrigeration Principles and System Components

When charging a zeotropic refrigerant blend into a system, the refrigerant should normally be withdrawn from the cylinder as a liquid because:

  1. Vapor charging increases the glide of the blend
  2. Liquid charging is always faster than vapor charging
  3. Vapor withdrawal can change blend composition by fractionation Correct answer.
  4. Liquid charging prevents oil foaming in the compressor crankcase

Explanation

Zeotropic blends have components with different boiling points, so vapor charging can remove the more volatile component first and alter the remaining mixture. Charging as liquid and throttling into the system helps maintain the intended composition.

Question 22Refrigeration Principles and System Components

A compressor that is slugging is experiencing:

  1. Low oil pressure caused by a clogged filter
  2. Liquid refrigerant or oil entering the cylinder Correct answer.
  3. High discharge pressure caused by air in the system
  4. Normal operation with slight superheat

Explanation

Slugging occurs when liquid rather than vapor reaches the compressor, which can damage valves and bearings. It is commonly caused by flooding, low superheat, or oil return problems.

Question 23Refrigeration Principles and System Components

A standing vacuum of 500 microns held for 30 minutes indicates:

  1. Excessive moisture that cannot be removed
  2. A refrigerant leak that must be located and repaired
  3. Atmospheric pressure in the system
  4. A satisfactory dehydration vacuum if it holds steady Correct answer.

Explanation

A deep vacuum in the 500-micron range is a typical target for dehydration, and a holding test confirms no rapid rise from moisture or leaks. A rising micron gauge would indicate moisture or a leak.

Question 24Refrigeration Principles and System Components

A reciprocating compressor with broken discharge valves will most likely show:

  1. Normal pressures with high subcooling
  2. Low superheat and high liquid line pressure
  3. Low discharge pressure and high suction Correct answer.
  4. High discharge pressure and low suction pressure

Explanation

Broken discharge valves allow high-pressure vapor to leak back into the cylinder, reducing the compressor's ability to build discharge pressure. The result is lower head pressure and higher suction pressure than normal.

Question 25Refrigeration Principles and System Components

Which symptom best indicates a restricted liquid line filter drier?

  1. High suction pressure with low superheat
  2. High subcooling with no measurable pressure drop across the drier
  3. A temperature drop across the drier plus sight-glass flash gas Correct answer.
  4. Low discharge pressure with low subcooling

Explanation

A restriction produces a pressure drop and a noticeable temperature drop across the drier as refrigerant flashes. Flash gas then appears downstream in the sight glass, and the evaporator may be starved.

Question 26Refrigeration Principles and System Components

The heat that changes a refrigerant from a saturated liquid to a saturated vapor without changing its temperature is called:

  1. Superheat
  2. Subcooling
  3. Latent heat Correct answer.
  4. Sensible heat

Explanation

Latent heat is the energy absorbed or rejected during a phase change at constant temperature. Sensible heat, by contrast, changes the refrigerant's temperature without causing a phase change.

Question 27Refrigeration Principles and System Components

The pressure of a saturated refrigerant in a closed container depends primarily on its:

  1. Speed of the vapor
  2. Volume of the container
  3. Mass of liquid in the container
  4. Temperature Correct answer.

Explanation

For a saturated refrigerant, pressure and temperature are directly related: at a given pressure the refrigerant boils and condenses at a fixed temperature. Container volume, liquid mass, and vapor velocity do not determine saturation pressure as long as both liquid and vapor are present.

Question 28Refrigeration Principles and System Components

In the evaporator, the refrigerant absorbs heat from the conditioned space mainly by:

  1. Condensing
  2. Compressing
  3. Boiling Correct answer.
  4. Subcooling

Explanation

The evaporator absorbs heat when liquid refrigerant boils into vapor. The phase change occurs at a nearly constant saturation temperature and provides most of the cooling effect.

Question 29Refrigeration Principles and System Components

A condenser operating with a higher-than-normal entering air temperature will most likely:

  1. Reduce compressor amps
  2. Lower head pressure
  3. Raise head pressure Correct answer.
  4. Increase subcooling

Explanation

A higher entering air temperature reduces the condenser's ability to reject heat, so the refrigerant condenses at a higher pressure and temperature. This raises head pressure and compressor load.

Question 30Refrigeration Principles and System Components

The primary function of an oil separator in a refrigeration system is to:

  1. Separate oil from discharge gas Correct answer.
  2. Separate liquid from suction gas
  3. Remove air from the refrigerant
  4. Remove moisture from the liquid line

Explanation

An oil separator is installed in the discharge line to trap oil entrained in hot discharge gas and return it to the compressor crankcase. Keeping oil out of the evaporator helps maintain heat transfer and compressor lubrication.

Question 31Refrigeration Principles and System Components

A compressor's volumetric efficiency decreases most directly when:

  1. The evaporator is oversized
  2. The condenser is clean
  3. Clearance volume is high Correct answer.
  4. The suction line is insulated

Explanation

Volumetric efficiency falls when gas left in the clearance volume re-expands on the suction stroke, reducing the fresh charge drawn in. Higher discharge pressure increases that re-expansion and lowers efficiency further.

Question 32Refrigeration Principles and System Components

A zeotropic refrigerant blend has a temperature glide of 8°F. During evaporation at constant pressure, the refrigerant temperature:

  1. It stays constant from inlet to outlet
  2. It is always equal to the dew point
  3. It changes from bubble to dew point Correct answer.
  4. It is read only at the compressor discharge

Explanation

A zeotropic blend changes temperature as it boils or condenses at constant pressure, a property called glide. The evaporator therefore runs between the bubble point at the inlet and the dew point at the outlet.

Question 33Refrigeration Principles and System Components

An externally equalized thermostatic expansion valve has its equalizer line connected to:

  1. The liquid line
  2. The suction line Correct answer.
  3. The evaporator inlet
  4. The compressor crankcase

Explanation

An externally equalized TXV uses the equalizer line to sense evaporator outlet pressure, compensating for pressure drop through the evaporator. It is connected to the suction line at the evaporator outlet.

Question 34Refrigeration Principles and System Components

In a pump-down cycle, the liquid-line solenoid valve closes to:

  1. Raise suction pressure during the pump-down
  2. Add refrigerant to the receiver
  3. Bypass the condenser during the pump-down
  4. Stop liquid flow and pump down the low side Correct answer.

Explanation

Closing the liquid-line solenoid stops the flow of liquid refrigerant to the metering device. The compressor then removes vapor from the low side until the low-pressure control stops it, which is the pump-down cycle.

Question 35Heating Equipment and Combustion Safety

What is the primary purpose of combustion air supplied to a natural gas furnace?

  1. To create the draft that moves flue gases up the chimney
  2. To supply oxygen needed for complete combustion Correct answer.
  3. To dilute the flue gases before they enter the vent
  4. To cool the heat exchanger during operation

Explanation

Combustion requires oxygen, and the burner receives it from combustion air. Dilution of flue gases is a separate function of the draft hood, and draft is produced by buoyancy and vent design.

Question 36Heating Equipment and Combustion Safety

Natural gas is odorized with which substance so that leaks can be detected by smell?

  1. Propane
  2. Sulfur dioxide
  3. Carbon monoxide
  4. Ethyl mercaptan Correct answer.

Explanation

A sulfur-bearing odorant such as ethyl mercaptan is added to natural gas so that even small leaks are noticeable. The odorant is not a combustion product and does not affect heating value.

Question 37Heating Equipment and Combustion Safety

Why is carbon monoxide produced by incomplete combustion especially hazardous?

  1. It has a sharp odor that warns occupants
  2. It forms a visible yellow cloud
  3. It is colorless and odorless and displaces oxygen in the blood Correct answer.
  4. It is lighter than air and collects near the ceiling

Explanation

Carbon monoxide has no color or odor and binds to hemoglobin far more readily than oxygen, so it can accumulate without warning. This makes CO monitoring and proper venting essential.

Question 38Heating Equipment and Combustion Safety

The draft hood on a Category I gas appliance serves mainly to:

  1. Stabilize draft and allow flue gases to spill if the vent is blocked Correct answer.
  2. Filter particulates from the flue gases
  3. Preheat combustion air entering the burners
  4. Increase the manifold gas pressure

Explanation

A draft hood isolates the appliance from chimney draft variations and provides dilution air. If the vent becomes blocked, flue gases spill at the hood rather than being forced into the space.

Question 39Heating Equipment and Combustion Safety

A thermocouple in a standing-pilot ignition system produces:

  1. A flame-rectification current
  2. 24 volts AC from the transformer
  3. A resistance change measured by the control
  4. A small millivolt signal when heated by the pilot flame Correct answer.

Explanation

A thermocouple generates a few millivolts when its hot junction is heated by the pilot flame. That signal holds the pilot valve open, and loss of flame drops the signal and closes the valve.

Question 40Heating Equipment and Combustion Safety

A flame sensor rod in a spark-ignition system proves main burner flame by:

  1. Sensing the rectified current through the flame Correct answer.
  2. Detecting ultraviolet light
  3. Measuring the temperature of the burner
  4. Monitoring gas pressure at the manifold

Explanation

The flame sensor uses flame rectification: the flame conducts a small DC current between the rod and burner ground. The control interprets that current as proof of flame.

Question 41Heating Equipment and Combustion Safety

A high-limit switch on a forced-air furnace is intended to:

  1. Start the blower when the plenum warms
  2. Shut off the gas valve if the pilot goes out
  3. Shut off the burner if the heat exchanger overheats Correct answer.
  4. Limit the manifold gas pressure

Explanation

The high-limit switch opens on excessive plenum temperature and breaks the burner circuit. It is a safety device against overheating, not a normal operating control.

Question 42Heating Equipment and Combustion Safety

The typical manifold pressure for a natural gas appliance is about:

  1. 3.5 in. w.c. Correct answer.
  2. 11 in. w.c.
  3. 6.5 in. w.c.
  4. 1.5 in. w.c.

Explanation

Most natural gas appliances are rated for about 3.5 in. w.c. manifold pressure. Propane appliances typically operate near 10 to 11 in. w.c.

Question 43Heating Equipment and Combustion Safety

When combustion air is supplied from outdoors through two permanent openings, NFPA 54 requires each opening to have a free area of at least:

  1. 1 sq in per 1,000 Btu/hr of input
  2. 1 sq in per 10,000 Btu/hr of input
  3. 1 sq in per 4,000 Btu/hr of input Correct answer.
  4. 1 sq in per 2,000 Btu/hr of input

Explanation

The two-opening method uses one opening near the floor and one near the ceiling, each sized at 1 sq in free area per 4,000 Btu/hr. The 2,000 Btu/hr figure applies to horizontal ducts, and 1,000 Btu/hr applies to indoor air infiltration.

Question 44Heating Equipment and Combustion Safety

A Category I gas appliance is best described as:

  1. Negative pressure, condensing, vented with a chimney liner
  2. Positive pressure, condensing, vented with PVC
  3. Negative pressure, non-condensing, vented with B-vent Correct answer.
  4. Positive pressure, non-condensing, vented with stainless steel

Explanation

Category I appliances operate with negative vent pressure and do not condense, so they are commonly vented with listed B-vent. Positive-pressure condensing appliances are Category IV.

Question 45Heating Equipment and Combustion Safety

A condensing furnace with a positive-pressure vent system is classified as:

  1. Category II
  2. Category III
  3. Category IV Correct answer.
  4. Category I

Explanation

Category IV appliances operate under positive vent pressure and condense, so they use listed plastic venting such as PVC or CPVC. Category III is positive pressure but non-condensing.

Question 46Heating Equipment and Combustion Safety

A barometric draft damper installed in a vent connector regulates draft by:

  1. Increasing the manifold gas pressure
  2. Admitting room air into the vent connector Correct answer.
  3. Closing off the chimney when the burner is off
  4. Mixing combustion air with gas at the burner

Explanation

The damper opens to admit room air and relieve excess draft, helping maintain a steady negative pressure at the appliance. It does not control gas pressure or burner air-fuel mixing.

Question 47Heating Equipment and Combustion Safety

Spillage from a draft hood is checked by:

  1. Measuring manifold pressure at the gas valve
  2. Reading the gas meter dial
  3. Holding a mirror or smoke source near the draft hood with the burner operating Correct answer.
  4. Checking the thermocouple output voltage

Explanation

A mirror or smoke source placed at the draft hood shows whether flue gases are escaping into the room instead of rising up the vent. Spillage indicates a draft or venting problem.

Question 48Heating Equipment and Combustion Safety

A sediment trap, or drip leg, is installed on a gas line to:

  1. Increase the gas pressure at the burner
  2. Collect dirt and scale before it reaches the gas valve Correct answer.
  3. Drain condensate from the flue gases
  4. Provide a draft measurement port

Explanation

A sediment trap is a capped pocket at the bottom of the gas line that catches dirt, pipe scale, and debris before they can foul the gas valve or orifices. It must be installed with the proper flow direction.

Question 49Heating Equipment and Combustion Safety

Which set of factors is used to size a natural gas piping system?

  1. Flue diameter, draft, and chimney height
  2. Water column, thermostat type, and blower speed
  3. Btu load, pipe length, pressure drop, and gas specific gravity Correct answer.
  4. Pipe color, vent height, and burner type

Explanation

Gas pipe sizing depends on the connected load, the equivalent length of run, the allowable pressure drop, and the specific gravity of the gas. Venting and thermostat details are unrelated to gas pipe capacity.

Question 50Heating Equipment and Combustion Safety

The approved method for checking a gas piping joint for leaks is:

  1. Pressurizing with air and listening for a hiss
  2. Applying soap bubble solution to the joint Correct answer.
  3. Smelling for the odorant at the joint
  4. Holding an open flame near the joint

Explanation

Leaks are located with a soap bubble solution or an approved electronic leak detector while the system is under pressure. Open flames are never acceptable for leak checking.