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Question 1Refrigeration Systems and Refrigerant Handling

According to ASHRAE Standard 34 safety classifications, what does the letter 'A' in an A1 refrigerant classification signify?

  1. Higher flammability
  2. Higher toxicity
  3. Lower flammability
  4. Lower toxicity Correct answer.

Explanation

ASHRAE Standard 34 uses a letter for toxicity and a number for flammability. Class A refrigerants have lower toxicity, while class B refrigerants have higher toxicity. The numeral 1 indicates lower flammability.

Question 2Refrigeration Systems and Refrigerant Handling

Which of the following refrigerants has an ozone depletion potential of zero?

  1. R-410A Correct answer.
  2. R-502
  3. R-12
  4. R-22

Explanation

R-410A is an HFC blend containing no chlorine, so its ozone depletion potential is zero. R-22 is an HCFC and R-12 is a CFC, both of which contain chlorine and have measurable ODP. R-502 is a blend containing a CFC component.

Question 3Refrigeration Systems and Refrigerant Handling

What is the primary function of the metering device in a vapor-compression refrigeration system?

  1. To regulate refrigerant flow into the evaporator and maintain the pressure difference Correct answer.
  2. To store excess refrigerant during low-load operation
  3. To raise the refrigerant pressure before it enters the condenser
  4. To remove moisture from the refrigerant

Explanation

The metering device creates the pressure drop between the high side and low side and regulates how much refrigerant enters the evaporator. It does not remove moisture, compress vapor, or store excess charge.

Question 4Refrigeration Systems and Refrigerant Handling

Refrigerant entering the evaporator of a properly operating refrigeration system is typically in which condition?

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

Explanation

After passing through the metering device, refrigerant pressure drops and some of the liquid flashes to vapor. The resulting low-pressure liquid-vapor mixture enters the evaporator to absorb heat.

Question 5Refrigeration Systems and Refrigerant Handling

What is the function of the condenser in a refrigeration cycle?

  1. To separate refrigerant vapor from liquid
  2. To reject heat from the refrigerant to the surrounding medium Correct answer.
  3. To absorb heat from the conditioned space
  4. To reduce refrigerant pressure before the evaporator

Explanation

The condenser receives high-pressure hot vapor from the compressor and rejects heat to the ambient air or water, causing the refrigerant to condense to liquid. Heat absorption occurs in the evaporator, not the condenser.

Question 6Refrigeration Systems and Refrigerant Handling

When filling a DOT recovery cylinder with recovered refrigerant, what is the maximum fill level by weight?

  1. 70 percent
  2. 90 percent
  3. 80 percent Correct answer.
  4. 60 percent

Explanation

DOT recovery cylinders are limited to 80 percent of their capacity by weight to leave room for liquid expansion as temperature rises. Overfilling can create hydraulic pressure and rupture the cylinder.

Question 7Refrigeration Systems and Refrigerant Handling

Superheat is best defined as the temperature of refrigerant vapor that is:

  1. Above its saturation temperature at the existing pressure Correct answer.
  2. Below its saturation temperature at the existing pressure
  3. Equal to its saturation temperature at the existing pressure
  4. Measured only at the compressor discharge

Explanation

Superheat is the amount by which vapor temperature exceeds the saturation temperature at the same pressure. It confirms that all liquid has boiled off before the vapor reaches the compressor.

Question 8Refrigeration Systems and Refrigerant Handling

What is the primary purpose of evacuating a refrigeration system with a vacuum pump before charging?

  1. To remove moisture and non-condensable gases from the system Correct answer.
  2. To test the system's high-pressure limit
  3. To add lubricating oil to the compressor
  4. To increase the system's refrigerant capacity

Explanation

Evacuation removes air, nitrogen, and moisture from the system so that non-condensables and water do not cause high head pressure, acid formation, or ice blockage. It is not a method of adding capacity or oil.

Question 9Refrigeration Systems and Refrigerant Handling

Liquid-line subcooling is calculated by subtracting the measured liquid-line temperature from the:

  1. Evaporator coil temperature
  2. Ambient air temperature
  3. Saturation temperature corresponding to the discharge pressure Correct answer.
  4. Saturation temperature corresponding to the suction pressure

Explanation

Subcooling is found by subtracting the measured liquid-line temperature from the saturation temperature corresponding to the discharge or condensing pressure. A positive value indicates liquid is cooler than the condensing temperature.

Question 10Refrigeration Systems and Refrigerant Handling

Why is dry nitrogen commonly used for pressure testing a refrigeration system?

  1. It combines with moisture to form a safe compound
  2. It is an inert gas that will not support combustion or add moisture Correct answer.
  3. It has a high ozone depletion potential
  4. It changes phase at room temperature to aid leak detection

Explanation

Dry nitrogen is inert, does not add moisture to the system, and will not support combustion. It is used with a pressure regulator to pressurize the system for leak detection.

Question 11Refrigeration Systems and Refrigerant Handling

Why must R-410A be charged into a system as a liquid rather than as a vapor?

  1. Vapor charging would remove the lubricant from the system
  2. R-410A is a near-azeotropic blend that can fractionate if charged as a vapor Correct answer.
  3. Liquid charging prevents compressor oil from foaming
  4. Liquid charging is required only for systems with a TXV

Explanation

R-410A is a near-azeotropic blend, and its components have different volatilities. Charging vapor can draw off a mixture that is not representative of the cylinder, so liquid charging is required to maintain the intended composition.

Question 12Refrigeration Systems and Refrigerant Handling

As the load on an evaporator increases, how does a properly functioning thermostatic expansion valve respond?

  1. It closes further to reduce refrigerant flow
  2. It opens further to maintain the set superheat Correct answer.
  3. It bypasses the condenser
  4. It remains in a fixed position regardless of load

Explanation

The TXV senses superheat at the evaporator outlet. When load increases, more refrigerant boils off and superheat rises, so the valve opens to increase flow and bring superheat back to its setting.

Question 13Refrigeration Systems and Refrigerant Handling

Liquid refrigerant slugging can damage a reciprocating compressor primarily because:

  1. Liquid refrigerant is incompressible and can cause mechanical impact Correct answer.
  2. Liquid refrigerant reacts with the compressor oil to form acid
  3. Liquid refrigerant increases the compressor's compression ratio
  4. Liquid refrigerant burns the motor windings

Explanation

Liquid refrigerant cannot be compressed like vapor and can cause hydraulic forces that damage valves, rods, and bearings. It can also wash oil from the compressor.

Question 14Refrigeration Systems and Refrigerant Handling

What is the purpose of a pump-down cycle in a refrigeration system?

  1. To add refrigerant to the system automatically
  2. To reduce condenser airflow at low ambient
  3. To pump refrigerant out of the low side and stop the compressor before shutdown Correct answer.
  4. To raise the evaporator pressure during defrost

Explanation

A pump-down cycle removes refrigerant from the low side and stores it in the high side or a receiver before the compressor stops. This limits the amount of refrigerant that can migrate into the compressor during off cycles.

Question 15Refrigeration Systems and Refrigerant Handling

What is a common symptom of non-condensable gases in a refrigeration system?

  1. Abnormally low discharge pressure
  2. Abnormally high discharge pressure and high condensing temperature Correct answer.
  3. Low suction superheat at the compressor
  4. Frequent compressor oil breakdown

Explanation

Non-condensable gases collect in the condenser and reduce the heat-transfer area, causing higher discharge pressure and condensing temperature. They do not lower discharge pressure or directly cause low superheat.

Question 16Refrigeration Systems and Refrigerant Handling

Which component is installed on the low-pressure side to prevent liquid refrigerant from reaching the compressor?

  1. Receiver
  2. Accumulator Correct answer.
  3. Liquid-line filter drier
  4. Oil separator

Explanation

An accumulator is installed on the suction line to trap liquid refrigerant and allow only vapor to reach the compressor. A receiver stores liquid on the high side.

Question 17Refrigeration Systems and Refrigerant Handling

Mineral oil is most commonly compatible with which type of refrigerant?

  1. Carbon dioxide
  2. HFC refrigerants such as R-410A
  3. HFO refrigerants such as R-1234yf
  4. HCFC refrigerants such as R-22 Correct answer.

Explanation

Mineral oil is miscible with HCFC refrigerants such as R-22 and is traditionally used in those systems. HFC and HFO refrigerants generally require synthetic lubricants such as POE or PAG.

Question 18Refrigeration Systems and Refrigerant Handling

Why is head pressure control needed in a refrigeration system operating at low ambient temperatures?

  1. To maintain sufficient pressure differential across the metering device Correct answer.
  2. To reduce compressor current draw
  3. To prevent the evaporator from freezing
  4. To increase the refrigerant charge

Explanation

At low ambient temperatures, condensing pressure can fall so low that the pressure difference across the metering device is insufficient for proper refrigerant flow. Head pressure control maintains that differential.

Question 19Refrigeration Systems and Refrigerant Handling

A standing vacuum test is performed after evacuation. If the micron gauge rises slowly and then stabilizes, the most likely cause is:

  1. Moisture in the system Correct answer.
  2. A faulty compressor
  3. Excess refrigerant oil
  4. A major refrigerant leak

Explanation

A vacuum reading that rises slowly and then levels off often indicates moisture is boiling off and being drawn out. A continuous rise after isolation more strongly suggests a leak.

Question 20Refrigeration Systems and Refrigerant Handling

When using a recovery machine to recover refrigerant from a system, the recovery cylinder should be:

  1. Filled completely to maximize efficiency
  2. Evacuated before use only if refrigerant is flammable
  3. Weighed during the recovery process Correct answer.
  4. Placed in direct sunlight to speed recovery

Explanation

Recovery cylinders must be weighed during recovery to ensure they are not overfilled beyond the 80 percent limit. They should also be rated for the refrigerant and kept away from heat.

Question 21Refrigeration Systems and Refrigerant Handling

Which of the following best describes temperature glide?

  1. The temperature rise across the condenser
  2. The temperature change of a zeotropic blend during phase change at constant pressure Correct answer.
  3. The difference between suction and discharge temperatures
  4. The difference between ambient and coil temperature

Explanation

Temperature glide is the change in temperature of a zeotropic blend as it changes phase at constant pressure. It occurs because the components have different boiling points.

Question 22Refrigeration Systems and Refrigerant Handling

A technician measures 500 microns after evacuation, isolates the system, and observes the gauge rise to 1500 microns within ten minutes. What does this indicate?

  1. The system has a leak or moisture present and requires further evacuation or repair Correct answer.
  2. The vacuum pump is too large for the system
  3. The system is ready for charging
  4. The micron gauge is calibrated in psig

Explanation

A rapid rise from 500 to 1500 microns after isolation indicates the vacuum is not holding, which can be caused by a leak or by moisture continuing to vaporize. Further leak checking or evacuation is required before charging.

Question 23Refrigeration Systems and Refrigerant Handling

When recovering refrigerant from a system that contains an A2L refrigerant, the technician must:

  1. Vent the refrigerant to atmosphere if the charge is small
  2. Recover the refrigerant only after raising system pressure with oxygen
  3. Use standard recovery equipment because all refrigerants are nonflammable
  4. Use recovery equipment rated for flammable refrigerants and eliminate ignition sources Correct answer.

Explanation

A2L refrigerants have flammability characteristics, so recovery equipment must be rated for flammable refrigerants and ignition sources must be controlled. Venting refrigerant to the atmosphere is prohibited.

Question 24Refrigeration Systems and Refrigerant Handling

When retrofitting an R-22 system to R-407C, which lubricant change is generally required?

  1. No lubricant is needed with R-407C
  2. The mineral oil must be replaced with polyolester (POE) oil Correct answer.
  3. Mineral oil can remain unchanged
  4. The system must be charged with PAG oil

Explanation

R-407C is an HFC blend and requires polyolester (POE) oil because mineral oil is not sufficiently miscible with HFC refrigerants. Residual mineral oil must be minimized during retrofit.

Question 25Refrigeration Systems and Refrigerant Handling

A system using a TXV has a suction superheat of 25°F (14 K) and low suction pressure. Which condition is most likely?

  1. Undercharge or restricted liquid line Correct answer.
  2. Failed condenser fan
  3. Too much compressor oil
  4. Overcharge of refrigerant

Explanation

High superheat combined with low suction pressure usually indicates the evaporator is starved of refrigerant, which can result from undercharge or a restriction in the liquid line. Overcharge and condenser problems would typically raise head pressure and reduce superheat.

Question 26Refrigeration Systems and Refrigerant Handling

In the ASHRAE safety classification system, what does a refrigerant designated A2L indicate?

  1. Low toxicity with no flammability under any condition
  2. High toxicity with rapid burning at room temperature
  3. Low toxicity with lower flammability than A2 or A3 refrigerants Correct answer.
  4. High toxicity with no flammability at any concentration

Explanation

The letter in the ASHRAE 34 designation rates toxicity (A = lower toxicity, B = higher toxicity) and the number rates flammability (1 = no flame propagation, 2 = flammable, 3 = highly flammable). The suffix L marks a refrigerant whose burning velocity and heat of combustion are low enough that it is classed as mildly flammable rather than fully flammable. A2L refrigerants therefore keep the low-toxicity rating of the A group while being less flammable than A2 or A3 materials.

Question 27Refrigeration Systems and Refrigerant Handling

How is a DOT recovery cylinder identified in the field?

  1. Green body with a white top
  2. Red body with a black top
  3. Gray body with a yellow top Correct answer.
  4. Yellow body with a gray top

Explanation

Industry practice and EPA guidance call for recovery cylinders to be gray with a yellow shoulder or top so they are not confused with virgin refrigerant cylinders. The cylinder must also carry the required marking identifying it as a recovery unit and listing the refrigerant it contains. Color coding is a communication aid only; the marked contents and the cylinder's pressure rating govern its use.

Question 28Refrigeration Systems and Refrigerant Handling

Why must recovered refrigerant never be mixed with a different refrigerant in the same cylinder?

  1. The mixture will freeze inside the recovery machine
  2. The cylinder relief device will not function with a blend
  3. Recovery cylinders are rated for only one refrigerant at a time
  4. The mixture cannot be reclaimed and must be destroyed Correct answer.

Explanation

Reclaimers must verify the composition of the refrigerant they process, and a cylinder of unknown mixed refrigerant cannot be tested to a recognized specification. Once refrigerants are blended in a recovery cylinder the contents are treated as waste and are destroyed rather than reclaimed. Keeping each recovered refrigerant in its own labeled cylinder preserves its value and its reclaimability.

Question 29Refrigeration Systems and Refrigerant Handling

What is the primary purpose of a crankcase heater on a refrigeration compressor?

  1. To maintain oil viscosity at the correct value while running
  2. To warm the suction vapor before it reaches the cylinders
  3. To keep crankcase oil warmer than the coldest part of the system Correct answer.
  4. To raise the discharge temperature during low-load operation

Explanation

When a compressor is off, refrigerant migrates to the crankcase and condenses in the oil, diluting it. A crankcase heater holds the oil above the temperature of the coldest system component so refrigerant boils out of the oil instead of accumulating there. Without it, startup can produce oil foaming, loss of lubrication, and liquid slugging.

Question 30Refrigeration Systems and Refrigerant Handling

Which method is appropriate for locating a small refrigerant leak on a system charged with an HFC?

  1. A pressure comparison between the high and low sides
  2. A halide torch, since it responds to every refrigerant
  3. An electronic detector designed for the refrigerant in use Correct answer.
  4. An open flame held near the suspected joint

Explanation

Electronic leak detectors are refrigerant-specific; the instrument must be capable of sensing the refrigerant actually in the system to respond reliably to small concentrations. Halide torches are unsuitable for HFCs because they depend on chlorine in the molecule and can produce toxic breakdown products. Other acceptable methods include ultrasonic instruments, fluorescent dye, and soap bubbles at accessible joints.

Question 31Refrigeration Systems and Refrigerant Handling

What is the function of the liquid receiver in a refrigeration system?

  1. It removes moisture and acids from the liquid line
  2. It stores liquid refrigerant for the expansion device as load varies Correct answer.
  3. It separates oil from discharge gas ahead of the condenser
  4. It collects liquid that has boiled off in the evaporator

Explanation

A receiver holds the system's liquid charge and supplies the expansion device with solid liquid as the load and the amount of refrigerant in circulation change. It also provides space to hold the charge during pump-down. It is a storage vessel, not a treatment device, so moisture and acid removal remain the job of the filter-drier.

Question 32Refrigeration Systems and Refrigerant Handling

A sight glass in the liquid line shows a continuous stream of bubbles while the system runs steadily under normal load. What does this most likely indicate?

  1. Air trapped inside the evaporator coil
  2. Excess refrigerant charge in the system
  3. Normal operation of the expansion valve
  4. Low refrigerant charge or a liquid-line restriction Correct answer.

Explanation

Bubbles in the liquid line mean the refrigerant is flashing before it reaches the metering device, which shows that subcooling has been lost. The usual causes are an undercharge or a restriction such as a plugged filter-drier or a partially closed valve. A clear glass with the system stable indicates the liquid is solid and subcooled.

Question 33Refrigeration Systems and Refrigerant Handling

Why is moisture considered especially harmful inside a refrigeration system?

  1. It raises the boiling point of the refrigerant and cuts capacity
  2. It coats the condenser coil and reduces heat rejection
  3. It forms acids with oil and refrigerant that attack the system from inside Correct answer.
  4. It increases the compressor's volumetric efficiency above design

Explanation

Water in a system reacts with refrigerant and lubricant to produce hydrochloric and hydrofluoric acids, which corrode metal, promote copper plating, and break down the oil. Moisture also freezes at the metering device and can plug the flow path. This is why a new filter-drier and a proper deep vacuum are required after any repair that exposes the system.

Question 34Refrigeration Systems and Refrigerant Handling

Under EPA Section 608, an appliance is classified as a small appliance when it is:

  1. Any appliance containing less than 50 pounds of refrigerant
  2. A commercial unit charged with more than 5 pounds of refrigerant
  3. Factory-charged, hermetically sealed, and holding 5 pounds or less Correct answer.
  4. Any residential air conditioner regardless of charge size

Explanation

The small-appliance category covers products that are factory-charged, hermetically sealed, and contain 5 pounds or less of refrigerant, such as household refrigerators, freezers, dehumidifiers, window units, and PTACs. Because the compressor and circuit are sealed at the factory, these units have their own recovery and evacuation requirements. Larger field-assembled equipment falls under the other appliance categories instead.

Question 35Refrigeration Systems and Refrigerant Handling

Before using a recovery cylinder, what should a technician verify?

  1. The cylinder's hydrostatic test date has not expired Correct answer.
  2. The cylinder is painted the same color as the refrigerant it will hold
  3. The cylinder has been purged with nitrogen at least once
  4. The pressure relief valve has been removed for servicing

Explanation

DOT refrigerant cylinders must be requalified by hydrostatic testing at intervals set by the specification stamped on the cylinder. A cylinder past its test date may not be filled or transported, even if it looks sound. The technician also confirms that the cylinder is an approved recovery cylinder, is labeled with the refrigerant it contains, and has a functioning relief device.

Question 36Refrigeration Systems and Refrigerant Handling

Why does the Clean Air Act prohibit knowingly venting refrigerant to the atmosphere?

  1. Refrigerant releases harm the ozone layer or the climate Correct answer.
  2. Vented refrigerant will ignite when it meets the atmosphere
  3. Venting causes the system to lose its lubricant charge
  4. The Act permits venting only during daylight hours

Explanation

Chlorofluorocarbons and hydrochlorofluorocarbons destroy stratospheric ozone, and all common refrigerants are potent greenhouse gases. Section 608 therefore requires recovery before opening a system and bans knowing venting except for limited de minimis releases. Recovery, recycling, and reclamation keep these compounds out of the atmosphere.

Question 37Refrigeration Systems and Refrigerant Handling

Why are suction lines on refrigeration systems pitched toward the compressor?

  1. To allow liquid refrigerant to drain back into the evaporator
  2. To keep the suction line colder than the evaporator outlet
  3. To reduce the pressure drop between the evaporator and the compressor
  4. To carry oil back to the compressor rather than let it pool Correct answer.

Explanation

Oil leaves the compressor with the discharge gas and must find its way back through the low side. Pitching horizontal suction runs toward the compressor, and using risers correctly, keeps oil moving instead of collecting in low spots where it would starve the compressor and reduce capacity. Proper slope is a piping requirement and does not replace an oil separator or an accumulator where one is specified.

Question 38Refrigeration Systems and Refrigerant Handling

What is the purpose of the dry nitrogen breaks used during a triple evacuation?

  1. They cool the compressor before the final evacuation stage
  2. They flush refrigerant oil out of the lines and into the receiver
  3. They absorb moisture from interior surfaces so the next evacuation removes it Correct answer.
  4. They raise system pressure so leaks can be located with soap bubbles

Explanation

Under a deep vacuum, moisture held on interior surfaces evaporates slowly and can leave the system wet even after the micron gauge settles. Breaking the vacuum with dry nitrogen raises the pressure and drives that moisture into the vapor so the following evacuation can carry it out. Repeating the cycle removes water much faster than a single long pump-down.

Question 39Refrigeration Systems and Refrigerant Handling

Refrigerant recovered from a system that suffered a compressor motor burnout should be:

  1. Mixed with virgin refrigerant to dilute the contaminants
  2. Recovered through a filter-drier and held for testing or recycling Correct answer.
  3. Returned to the system once the new compressor is installed
  4. Vented, because it is contaminated beyond any use

Explanation

A burnout leaves acid, sludge, and particulate matter suspended in the refrigerant and oil. Recovering through an in-line filter-drier captures much of that material, and the recovered refrigerant is then tested and recycled or reclaimed before reuse. Venting is prohibited, and returning the contaminated charge or diluting it with virgin refrigerant would reintroduce the acids and debris that destroyed the first compressor.

Question 40Refrigeration Systems and Refrigerant Handling

A zeotropic blend with a measurable temperature glide develops a leak in the vapor space of a system. What happens to the refrigerant left behind?

  1. The remaining liquid grows richer in the less volatile components Correct answer.
  2. Its composition is unchanged because blends leak uniformly as a mixture
  3. The remaining charge becomes a near-azeotrope with essentially no glide
  4. The remaining liquid grows richer in the more volatile components

Explanation

In a zeotropic blend the components have different boiling points, so vapor in the space above the liquid is richer in the more volatile fraction. A leak from the vapor space removes that fraction preferentially, leaving the remaining liquid shifted toward the less volatile components. The system's composition, glide, and performance therefore drift, which is why blends must be charged as liquid and why a repeated vapor leak calls for a full charge replacement.

Question 41Electrical and Controls

A 24-volt control circuit is connected to a 48-ohm resistive load. What current does the load draw?

  1. 0.05 A
  2. 1,152 A
  3. 2 A
  4. 0.5 A Correct answer.

Explanation

Ohm's law states that current equals voltage divided by resistance. Dividing 24 volts by 48 ohms gives 0.5 ampere.

Question 42Electrical and Controls

In a conventional 24-volt thermostat cable, which conductor is used to energize the indoor blower on a call for fan?

  1. W
  2. R
  3. Y
  4. G Correct answer.

Explanation

The G terminal and its conductor control the indoor blower on a fan-only or continuous-fan call. R supplies the 24-volt hot leg, Y calls for compressor operation, and W calls for heat.

Question 43Electrical and Controls

What is the standard control voltage for a residential forced-air furnace control circuit?

  1. 5 VDC
  2. 12 VDC
  3. 120 VAC
  4. 24 VAC Correct answer.

Explanation

Residential equipment uses a step-down transformer to provide a 24-volt alternating-current control circuit. This low voltage operates thermostats, gas valves, relays, and contactor coils.

Question 44Electrical and Controls

What is the function of the step-down transformer in a residential air handler?

  1. Reduces 120 VAC to 24 VAC for the control circuit Correct answer.
  2. Steps 24 volts up to 120 volts for the blower motor
  3. Supplies 240 volts to the compressor contactor
  4. Rectifies 120 VAC to 24 VDC for the gas valve

Explanation

A step-down transformer takes the higher line voltage supplied to the unit and produces a lower secondary voltage for the controls. In residential equipment that secondary is nominally 24 volts AC.

Question 45Electrical and Controls

Which safety control stops the compressor when suction pressure falls below a safe value?

  1. High-pressure switch
  2. Defrost thermostat
  3. Condensate float switch
  4. Low-pressure switch Correct answer.

Explanation

A low-pressure switch senses suction pressure and opens the control circuit when pressure drops below its setpoint, protecting the compressor from operation with an inadequate refrigerant charge. A high-pressure switch performs the opposite function on the discharge side.

Question 46Electrical and Controls

An ohmmeter continuity check on a motor winding should be made with the:

  1. Circuit energized and the motor running
  2. Meter set to read AC volts
  3. Motor capacitor left connected across the winding
  4. Power removed and the winding isolated Correct answer.

Explanation

Resistance and continuity measurements require an de-energized circuit, and the winding should be isolated so parallel paths do not affect the reading. Testing with power applied can damage the meter and is unsafe.

Question 47Electrical and Controls

Which device is intended to open a circuit automatically when current exceeds its rating?

  1. Potential relay
  2. Thermostat heat anticipator
  3. Transformer
  4. Circuit breaker Correct answer.

Explanation

A circuit breaker contains a thermal or magnetic element that trips when current exceeds the device rating, protecting the conductors and components downstream. A fuse performs the same overcurrent protection function.

Question 48Electrical and Controls

In a ladder diagram, a rung is normally read:

  1. Bottom to top, following wire numbers
  2. From the load back to the switch
  3. Right to left, from neutral to line
  4. Left to right, from power to neutral Correct answer.

Explanation

Ladder diagrams are drawn with the power source on the left and the neutral or common on the right, and each rung is traced from the source through the switches and loads to the return. This convention allows the technician to follow the circuit in the direction current flows.

Question 49Electrical and Controls

A transformer is rated 40 VA with a 24-volt secondary. What is the maximum secondary current it can supply?

  1. 0.6 A
  2. 3.33 A
  3. 960 A
  4. 1.67 A Correct answer.

Explanation

For a transformer, volt-amperes equal secondary voltage multiplied by secondary current. Rearranging gives 40 VA divided by 24 volts, which equals about 1.67 amperes.

Question 50Electrical and Controls

A contactor coil measures infinite resistance on an ohmmeter. What is the most likely result on a call for cooling?

  1. The compressor starts but the condenser fan does not
  2. The contactor chatters but the compressor starts
  3. The coil will overheat and close the contacts
  4. The contactor will not pull in Correct answer.

Explanation

An infinite resistance reading means the coil winding is open, so no current can flow and no magnetic field is produced to close the contacts. With the contacts open, the compressor circuit remains de-energized.