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Question 1Refrigeration Principles and System Components

For a pure refrigerant in a closed system, the saturation pressure is determined by which of the following?

  1. The pipe diameter
  2. The compressor speed
  3. The refrigerant temperature Correct answer.
  4. The receiver liquid level

Explanation

Saturation pressure and saturation temperature are directly linked for a pure refrigerant; once one is known, the other is fixed. System volume, component speed and piping size do not change that relationship.

Question 2Refrigeration Principles and System Components

Heat that is added to or removed from a substance and causes a change in its temperature is called:

  1. Latent heat
  2. Sensible heat Correct answer.
  3. Heat of fusion
  4. Specific heat

Explanation

Sensible heat produces a temperature change that can be measured with a thermometer, with no change of state. Latent heat, by contrast, changes state at a constant temperature.

Question 3Refrigeration Principles and System Components

The function of the condenser in a vapour-compression refrigeration cycle is to:

  1. Meter refrigerant into the evaporator
  2. Reject heat and condense the vapour Correct answer.
  3. Absorb heat from the conditioned space
  4. Raise the pressure of the refrigerant vapour

Explanation

The condenser rejects the heat picked up in the evaporator plus the heat of compression, changing high-pressure vapour into high-pressure liquid. Rejection occurs to ambient air or to condenser water.

Question 4Refrigeration Principles and System Components

In a direct-expansion evaporator, the refrigerant:

  1. Absorbs heat and boils to a vapour Correct answer.
  2. Condenses and gives up heat
  3. Remains a liquid throughout the coil
  4. Is compressed to a higher pressure

Explanation

Low-pressure refrigerant enters the DX coil as a liquid-vapour mixture and boils as it travels through, absorbing heat from the air or fluid being cooled. It leaves the coil as vapour, usually slightly superheated.

Question 5Refrigeration Principles and System Components

The compressor's main function in a refrigeration system is to:

  1. Increase refrigerant pressure Correct answer.
  2. Reject heat to the outdoor air
  3. Control refrigerant flow to the coil
  4. Remove moisture from the refrigerant

Explanation

The compressor is the pump of the cycle: it raises the refrigerant pressure so the condenser can reject heat at a usable temperature, and it keeps refrigerant moving around the circuit.

Question 6Refrigeration Principles and System Components

The metering device in a refrigeration circuit:

  1. Increases the pressure of the liquid refrigerant
  2. Stores liquid refrigerant for the off cycle
  3. Drops the pressure and meters flow Correct answer.
  4. Separates oil from the discharge gas

Explanation

The metering device creates the pressure difference between the high side and low side and regulates how much liquid refrigerant enters the evaporator. Without it the two sides could not be maintained at different pressures.

Question 7Refrigeration Principles and System Components

R-134a belongs to which refrigerant family?

  1. CFC
  2. Natural refrigerant
  3. HFC Correct answer.
  4. HCFC

Explanation

R-134a contains hydrogen, fluorine and carbon but no chlorine, which places it in the hydrofluorocarbon (HFC) family. HFCs have no ozone-depleting chlorine but still have global warming potential.

Question 8Refrigeration Principles and System Components

The heat absorbed by a refrigerant while it boils at a constant saturation temperature is called:

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

Explanation

Boiling takes place at a constant saturation temperature, so the heat added changes the refrigerant's state instead of its temperature. That hidden heat is the latent heat of vaporization.

Question 9Refrigeration Principles and System Components

Superheat is best defined as:

  1. Vapour temperature above the saturation temperature Correct answer.
  2. The pressure difference across the metering device
  3. The temperature drop across the evaporator coil
  4. Liquid temperature below the saturation temperature

Explanation

Superheat compares the measured vapour temperature with the saturation temperature corresponding to the pressure at that same point. It confirms that all liquid has boiled off before the vapour reaches the compressor.

Question 10Refrigeration Principles and System Components

Subcooling is measured as the difference between the:

  1. Suction line temperature and evaporating temperature
  2. Entering and leaving air temperatures of the coil
  3. Condensing temperature and liquid line temperature Correct answer.
  4. Discharge temperature and condensing temperature

Explanation

Subcooling is measured at the condenser outlet by comparing the liquid line temperature with the saturation temperature for the condensing pressure. It shows how far the liquid has been cooled below saturation.

Question 11Refrigeration Principles and System Components

A thermostatic expansion valve controls refrigerant flow in order to maintain a constant:

  1. Superheat at the evaporator outlet Correct answer.
  2. Condensing pressure in the condenser
  3. Evaporator pressure at the coil inlet
  4. Subcooling at the condenser outlet

Explanation

The TXV senses evaporator outlet temperature and pressure with its bulb and equalizer, then modulates the valve opening to hold a constant superheat as the load changes.

Question 12Refrigeration Principles and System Components

The purpose of a suction line accumulator is to:

  1. Prevent liquid from reaching the compressor Correct answer.
  2. Separate oil from the discharge gas
  3. Store liquid refrigerant for the defrost cycle
  4. Remove moisture from the liquid line

Explanation

An accumulator on the suction line traps any liquid that carries over from the evaporator and returns it gradually as vapour. This protects the compressor from slugging and from oil dilution.

Question 13Refrigeration Principles and System Components

A filter drier installed in the liquid line is intended to:

  1. Reduce the refrigerant pressure
  2. Trap moisture and solid contaminants Correct answer.
  3. Provide a reservoir of liquid refrigerant
  4. Show the refrigerant charge level

Explanation

The filter drier holds a desiccant that absorbs moisture and a screen that catches solid particles, protecting the metering device and compressor from damage and ice blockage.

Question 14Refrigeration Principles and System Components

Bubbles seen in the liquid line sight glass of a running system most often indicate:

  1. Excess subcooling in the condenser
  2. A low refrigerant charge Correct answer.
  3. Too much oil in the crankcase
  4. A restricted suction line filter

Explanation

Continuous bubbles reveal flash gas in the liquid line, which most commonly results from a shortage of refrigerant. A severe restriction can produce a similar appearance, so other readings are used to confirm.

Question 15Refrigeration Principles and System Components

Which lubricant is normally used with HFC refrigerants such as R-410A?

  1. Polyolester (POE) oil Correct answer.
  2. Alkylbenzene oil
  3. Mineral oil
  4. Castor oil

Explanation

HFC refrigerants are not miscible with mineral oil, so polyolester oil is used because it mixes with HFCs and returns with the refrigerant. POE is hygroscopic and must be kept tightly sealed.

Question 16Refrigeration Principles and System Components

A zeotropic refrigerant blend such as R-407C is characterized by:

  1. A temperature glide while boiling and condensing Correct answer.
  2. A single saturation temperature at all pressures
  3. Containing only one component
  4. Being flammable at room temperature

Explanation

The components of a zeotropic blend have different boiling points, so the mixture evaporates and condenses over a temperature range called glide. Because of glide, these blends must be charged as a liquid to avoid fractionation.

Question 17Refrigeration Principles and System Components

The crankcase heater on a compressor is used mainly to:

  1. Heat the discharge line during defrost
  2. Raise the evaporating temperature
  3. Stop refrigerant migrating into the oil Correct answer.
  4. Warm the suction gas before compression

Explanation

The heater keeps the crankcase oil warmer than the coldest part of the system so refrigerant that migrated during the off cycle boils off instead of condensing in the oil. This prevents oil dilution and liquid slugging on start-up.

Question 18Refrigeration Principles and System Components

A pump-down cycle is used to:

  1. Purge air from the receiver
  2. Empty the evaporator before shutdown Correct answer.
  3. Increase the capacity of the condenser
  4. Raise the suction pressure before start-up

Explanation

Pump-down keeps the compressor running after the thermostat is satisfied until a low-pressure control stops it, drawing the refrigerant into the high side. The evaporator is left empty so liquid cannot migrate to the compressor during the off cycle.

Question 19Refrigeration Principles and System Components

A capillary tube metering device is best suited to:

  1. Systems that require adjustable superheat
  2. Systems using a flooded evaporator
  3. Large commercial systems with varying loads
  4. Small sealed appliances with steady loads Correct answer.

Explanation

A capillary tube is a fixed restrictor matched to one design operating point, so it suits small factory-charged units where load and charge are closely controlled. It cannot adjust to widely changing conditions.

Question 20Refrigeration Principles and System Components

Compression ratio is calculated by dividing the absolute discharge pressure by the:

  1. Condensing temperature
  2. Absolute discharge temperature
  3. Absolute suction pressure Correct answer.
  4. Gauge suction pressure

Explanation

Compression ratio compares the absolute discharge pressure with the absolute suction pressure. Each gauge reading must have atmospheric pressure added before the division is done.

Question 21Refrigeration Principles and System Components

A system has a gauge suction pressure of 62 psig and a gauge discharge pressure of 202 psig. Using 14.7 psi for atmospheric pressure, what is the compression ratio?

  1. About 2.6
  2. About 3.3
  3. About 3.0
  4. About 2.8 Correct answer.

Explanation

Add 14.7 psi to each gauge reading to get absolutes: 216.7 psia discharge and 76.7 psia suction. Dividing 216.7 by 76.7 gives approximately 2.83.

Question 22Refrigeration Principles and System Components

A system with a fixed orifice shows low suction pressure, high superheat, low head pressure and continuous bubbles in the sight glass. The most likely cause is:

  1. An overcharge of refrigerant
  2. An undercharge of refrigerant Correct answer.
  3. A restricted liquid line drier
  4. A failed condenser fan motor

Explanation

Low suction pressure with high superheat together with low head pressure and flash gas is the classic signature of a system short of refrigerant. A restriction can also raise superheat, but it usually shows a temperature drop across the restriction rather than bubbles in the sight glass.

Question 23Refrigeration Principles and System Components

A system that has air trapped in the condenser will typically show:

  1. High suction pressure and low head pressure
  2. High head pressure and high subcooling Correct answer.
  3. Low head pressure with high liquid subcooling
  4. Low head pressure and low superheat

Explanation

Non-condensable gases such as air collect in the condenser, occupy volume and drive the discharge and head pressure up. Because they do not condense, the liquid at the condenser outlet is subcooled more than normal.

Question 24Refrigeration Principles and System Components

The purpose of a hot gas bypass on a DX system is to:

  1. Purge non-condensable gases from the condenser
  2. Raise the condensing temperature in cold weather
  3. Speed up defrost of the outdoor coil
  4. Prevent coil icing at light loads Correct answer.

Explanation

Hot gas bypass admits discharge gas to the evaporator inlet so suction pressure and coil temperature stay up when the load falls below the compressor's minimum capacity. This prevents coil icing and short cycling.

Question 25Refrigeration Principles and System Components

An externally equalized thermostatic expansion valve is selected when:

  1. The liquid line is unusually long
  2. The system also uses a capillary tube
  3. The evaporator is located above the condenser
  4. The evaporator has a large pressure drop Correct answer.

Explanation

An externally equalized valve senses evaporator outlet pressure through an equalizer line instead of internal valve-body pressure. This keeps the superheat setting accurate when the coil or its distributor has a significant pressure drop.

Question 26Refrigeration Principles and System Components

Which statement best describes how a scroll compressor raises refrigerant pressure?

  1. Two interleaved spiral wraps trap gas in crescent-shaped pockets that are swept toward the center as one wrap orbits Correct answer.
  2. A piston moves back and forth inside a cylinder, and spring-loaded reed valves control the flow of gas into and out of the cylinder
  3. Rolling elements move eccentrically inside a cylinder while a single spring-loaded blade slides in and out to seal the chamber
  4. Impeller blades fling the gas outward at high velocity, and a diffuser converts that velocity into static pressure

Explanation

A scroll compressor uses two mating spiral wraps; one is fixed and the other orbits without rotating, so gas is trapped in crescent pockets that are continuously displaced inward and reduced in volume. Because the pockets empty through a fixed discharge port, the action is continuous and requires no suction or discharge reed valves.

Question 27Refrigeration Principles and System Components

As refrigerant travels through an air-cooled condenser coil, in what order does it reject heat?

  1. Subcooling, then condensing, then desuperheating
  2. Desuperheating, then subcooling, then condensing
  3. Condensing, then desuperheating, then subcooling
  4. Desuperheating, then condensing, then subcooling Correct answer.

Explanation

Hot discharge gas enters the coil above its saturation temperature, so it first gives up sensible heat and is desuperheated to saturation. It then condenses at essentially constant temperature, releasing latent heat, and finally the liquid loses a little more sensible heat in the last portion of the coil, leaving subcooled.

Question 28Refrigeration Principles and System Components

On a pressure-enthalpy diagram of a basic vapor-compression cycle, what does the horizontal evaporation segment represent?

  1. The work of compression added to the vapor
  2. The net refrigerating effect per unit mass of refrigerant Correct answer.
  3. The fraction of flash gas produced across the metering device
  4. The total heat rejected by the condenser coil

Explanation

The evaporation segment runs from the enthalpy of the mixture leaving the metering device to the enthalpy of the vapor leaving the evaporator, and that enthalpy difference is the heat each unit mass absorbs to produce useful cooling. The vertical compression line represents compressor work, while the condenser segment represents heat rejected.

Question 29Heating Systems (Gas, Oil, Electric, and Heat Pumps)

A natural gas furnace that is properly adjusted typically operates with a manifold pressure closest to which value?

  1. 3.5 psi
  2. 0.5 in. w.c.
  3. 11 in. w.c.
  4. 3.5 in. w.c. Correct answer.

Explanation

Most residential natural gas appliances are rated for a manifold pressure of about 3.5 in. w.c., which is set by the gas valve regulator. Manifold pressure is always measured in inches of water column with a manometer, not in psi.

Question 30Heating Systems (Gas, Oil, Electric, and Heat Pumps)

Compared with natural gas, liquefied petroleum (LP) gas requires a burner orifice that is:

  1. larger, because LP gas has a much lower heating value per cubic foot than natural gas
  2. the same size, because orifices do not depend on the fuel
  3. smaller, since LP gas carries more Btu per cubic foot Correct answer.
  4. not used, because LP burners do not meter gas

Explanation

LP gas has a much higher heating value per cubic foot than natural gas, so a smaller metering hole delivers the same input rate. Orifices are fuel-specific, and a gas conversion always requires the correct orifices plus the proper manifold pressure.

Question 31Heating Systems (Gas, Oil, Electric, and Heat Pumps)

A heat pump operating in the heating mode uses which coil as the evaporator?

  1. The accumulator
  2. Both coils acting as evaporators at once
  3. The outdoor coil Correct answer.
  4. The indoor coil

Explanation

In heating, the reversing valve directs hot discharge gas to the indoor coil, making it the condenser, while the outdoor coil absorbs heat from outside air and acts as the evaporator. The roles of the two coils swap when the unit switches to cooling.

Question 32Heating Systems (Gas, Oil, Electric, and Heat Pumps)

Electric resistance heat has a coefficient of performance (COP) of approximately:

  1. 1.0 Correct answer.
  2. 3.0
  3. 0.5
  4. 1.5

Explanation

Resistance elements convert essentially all of the electrical energy supplied into heat, so one unit of energy yields one unit of heat and the COP is about 1.0. Heat pumps achieve higher values because they move heat rather than creating it.

Question 33Heating Systems (Gas, Oil, Electric, and Heat Pumps)

Which device proves the standing pilot flame on a conventional gas furnace before the main gas valve is allowed to open?

  1. A thermocouple Correct answer.
  2. A flame rollout switch
  3. A cad cell
  4. A hot surface igniter

Explanation

A thermocouple heated by the pilot generates a small millivolt signal that holds the pilot safety valve open; loss of the pilot drops the signal and shuts the gas off. It is a flame-proving device rather than an ignition source.

Question 34Heating Systems (Gas, Oil, Electric, and Heat Pumps)

The capacity of an oil burner nozzle is rated in:

  1. Cubic feet per minute
  2. Gallons per hour Correct answer.
  3. Inches of mercury
  4. Pounds per square inch

Explanation

Nozzle capacity is stated in gallons per hour at a reference pump pressure, usually 100 psi, along with a spray angle and pattern. The actual firing rate changes if the pump pressure differs from the reference pressure.

Question 35Heating Systems (Gas, Oil, Electric, and Heat Pumps)

In a typical residential air-source heat pump, auxiliary (backup) heat is most commonly provided by:

  1. A gas-fired booster burner
  2. An additional compressor
  3. A desuperheater coil
  4. Electric resistance elements Correct answer.

Explanation

Auxiliary heat is normally a bank of electric resistance elements mounted in the indoor air handler or duct, staged on when the heat pump cannot keep up. They are inexpensive to install but costly to operate compared with the compressor.

Question 36Heating Systems (Gas, Oil, Electric, and Heat Pumps)

The primary function of a draft hood on a natural-draft gas appliance is to:

  1. Increase the flue gas temperature so draft becomes stronger
  2. Regulate the gas manifold pressure
  3. Stabilize draft and dilute flue products with room air Correct answer.
  4. Filter flue products before they enter the vent

Explanation

The draft hood isolates the appliance from chimney draft variations and mixes room air with the flue gases, which prevents downdrafts from disturbing combustion. Dilution also lowers the dew point of the flue products so they leave the appliance without condensing.

Question 37Heating Systems (Gas, Oil, Electric, and Heat Pumps)

A furnace rated at 90% AFUE or higher typically uses which vent material?

  1. Type B double-wall metal vent
  2. An unlined masonry chimney flue
  3. PVC or CPVC plastic pipe Correct answer.
  4. Single-wall galvanized steel

Explanation

Condensing furnaces cool the flue products below the dew point, so the vent carries acidic condensate at low temperature; plastic pipe resists that attack. Metal vents and masonry would be corroded by the condensate.

Question 38Heating Systems (Gas, Oil, Electric, and Heat Pumps)

Flame rectification proves the presence of a burner flame by sensing:

  1. Light emitted by the flame
  2. The pressure change in the manifold
  3. A small direct current flowing through the flame Correct answer.
  4. The temperature rise across the heat exchanger

Explanation

The flame conducts current in one direction, so an AC voltage applied to the flame rod produces a small DC microamp signal that the control module reads as proof of flame. Loss of flame removes the signal and the gas valve closes.

Question 39Heating Systems (Gas, Oil, Electric, and Heat Pumps)

On an oil burner, the cad cell is used to:

  1. Detect flame light and signal the primary control Correct answer.
  2. Ignite the fuel-air mixture
  3. Measure carbon dioxide in the flue gas
  4. Regulate oil pump pressure

Explanation

The cad cell is a light-sensitive resistor that drops in resistance when it sees flame, telling the primary control that ignition occurred. If no light is sensed during the trial period, the control locks out and shuts off the burner.

Question 40Heating Systems (Gas, Oil, Electric, and Heat Pumps)

If the nozzle is unchanged and the oil pump pressure is increased, the burner firing rate will:

  1. Decrease
  2. Increase by roughly the square root of the pressure ratio Correct answer.
  3. Remain exactly the same
  4. Increase in direct proportion to the pressure

Explanation

Nozzle flow varies with the square root of the pressure differential, so raising pump pressure above the rated value increases flow less than proportionally. Burner manufacturers publish a pressure/nozzle chart for setting the desired firing rate.

Question 41Heating Systems (Gas, Oil, Electric, and Heat Pumps)

During the defrost cycle of an air-source heat pump operating in the heating mode, the outdoor fan normally:

  1. Shuts off Correct answer.
  2. Reverses direction
  3. Cycles on and off every minute
  4. Runs at high speed

Explanation

Stopping the outdoor fan reduces the heat added to the frosted coil so the hot discharge gas from the compressor can melt the frost quickly. The fan restarts when defrost terminates and the unit returns to normal heating.

Question 42Heating Systems (Gas, Oil, Electric, and Heat Pumps)

The balance point of a heat pump system is the outdoor temperature at which:

  1. Defrost is initiated by the time-temperature control
  2. The compressor is locked out by the low-pressure control
  3. Auxiliary heat is permanently disabled
  4. Heat pump capacity equals the building heat loss Correct answer.

Explanation

At the balance point the heat pump delivers exactly as much heat as the house loses, so no backup heat is needed. Below that temperature the building load exceeds heat pump capacity and auxiliary heat must make up the difference.

Question 43Heating Systems (Gas, Oil, Electric, and Heat Pumps)

The function of the high-limit switch on a gas furnace is to:

  1. Prevent the burner from operating below the flue gas dew point
  2. Limit the manifold pressure at high altitude
  3. Open the burner circuit if the bonnet temperature becomes excessive Correct answer.
  4. Stop the blower when the thermostat is satisfied

Explanation

A high-limit switch is a temperature-actuated safety that breaks the burner circuit when plenum temperature rises above its setpoint, protecting the heat exchanger from overheating. It may be automatic reset or, in some designs, manual reset.

Question 44Heating Systems (Gas, Oil, Electric, and Heat Pumps)

The customary allowance for combustion, dilution, and ventilation air for an unconfined indoor space is:

  1. 20 cubic feet per 1,000 Btu/hr of input
  2. 50 cubic feet per 1,000 Btu/hr of input Correct answer.
  3. 5 cubic feet per 1,000 Btu/hr of input
  4. 100 cubic feet per 1,000 Btu/hr of input

Explanation

The standard rule of thumb for an unconfined space is 50 cubic feet of volume per 1,000 Btu/hr of appliance input, based on normal air infiltration. Confined spaces require engineered openings or outdoor air.

Question 45Heating Systems (Gas, Oil, Electric, and Heat Pumps)

A combustion analyzer shows 9% oxygen in the flue gas of a natural gas furnace. This reading indicates:

  1. More excess air than necessary Correct answer.
  2. Unburned oil vapor in the flue products
  3. Perfect combustion with no excess air at all
  4. A shortage of combustion air

Explanation

Complete combustion with no excess air would leave almost no oxygen in the flue gas, and normal setup usually runs a few percent. A 9% reading shows a large amount of excess air diluting the products, which carries heat up the flue and lowers efficiency.

Question 46Heating Systems (Gas, Oil, Electric, and Heat Pumps)

When checking the charge of a heat pump in the heating mode by superheat, the superheat is measured at the:

  1. Discharge line at the compressor
  2. Liquid line leaving the indoor coil
  3. Suction line leaving the outdoor coil Correct answer.
  4. Liquid line leaving the outdoor coil

Explanation

In heating the outdoor coil is the evaporator, so superheat is the difference between the suction-line temperature and the saturation temperature at that coil. Measuring superheat at the evaporator outlet confirms the coil is properly fed with refrigerant.

Question 47Heating Systems (Gas, Oil, Electric, and Heat Pumps)

A flame rollout switch on a gas furnace is typically:

  1. An automatically resetting thermal switch
  2. A thermocouple that senses the pilot flame
  3. A pressure switch that senses flue draft
  4. A manually reset switch that opens when flame escapes the burner box Correct answer.

Explanation

Rollout switches are temperature devices mounted at the burner opening that trip when flames spill out, usually from a blocked flue or restricted combustion air. Most are manual reset so the cause must be found before the furnace can be restarted.

Question 48Heating Systems (Gas, Oil, Electric, and Heat Pumps)

The main reason a condensing furnace can exceed 90% AFUE while a conventional furnace is limited to about 80% is that the condensing furnace:

  1. Operates with a higher flue gas temperature
  2. Burns a fuel with a higher Btu content
  3. Recovers latent heat by condensing water vapor in the flue products Correct answer.
  4. Uses a larger blower to reduce standby losses

Explanation

Burning gas produces water vapor that carries latent heat; a conventional furnace sends that heat up the flue. A condensing furnace has a secondary heat exchanger that cools the products below the dew point, releasing that latent heat into the airstream.

Question 49Heating Systems (Gas, Oil, Electric, and Heat Pumps)

An oil burner puffs back on startup. Which condition most directly produces this?

  1. A nozzle rated below the burner's firing rate
  2. Excessive combustion air from an oversized draft regulator
  3. A cad cell receiving too much light
  4. Fuel accumulating in the combustion chamber before ignition Correct answer.

Explanation

Delayed ignition lets oil collect in the chamber; when it finally lights, the sudden burning of the accumulated fuel drives flame and pressure back out the burner opening. Ignition timing, electrode settings, and proper shutdown to prevent after-drip are the usual checkpoints.

Question 50Heating Systems (Gas, Oil, Electric, and Heat Pumps)

As outdoor temperature falls from 47°F to about 17°F, an air-source heat pump's heating capacity and coefficient of performance typically:

  1. Both decrease Correct answer.
  2. Capacity increases while COP decreases
  3. Both remain nearly constant
  4. Capacity decreases while COP increases

Explanation

A lower outdoor temperature means less heat is available to absorb at the outdoor coil, so both capacity and efficiency fall. That is why auxiliary heat is staged on as the balance point is approached.