Question 1

The outlet of the metering device is usually the coolest part of the system under normal operating conditions.

Accepted Answer

The metering device in a refrigeration system reduces the pressure of the refrigerant, causing it to expand and cool down. As a result, the outlet of the metering device is typically the coolest part of the system, as the refrigerant has not yet absorbed heat from the surrounding environment.

Question 2

During a refrigerant system performance test it is noticed that both high-side and low-side pressure readings are about the same.Which of the following could be the possible cause?

Accepted Answer

A faulty compressor can cause both high-side and low-side pressure readings to be about the same, indicating it is not compressing the refrigerant effectively.

Question 3

Which of the following could cause very low pressures on the low side of a system equipped with an expansion valve?

Accepted Answer

If the expansion valve is stuck closed, then refrigerant cannot flow through it and into the evaporator, resulting in very low pressures on the low side of the system. The other choices may cause other issues with the system, but they would not necessarily cause low pressures on the low side with an expansion valve.

Question 4

R-134a has the exact same temperature and pressure relationship as R-12.

Accepted Answer

R-134a and R-12 have different chemical compositions, leading to different temperature and pressure relationships for each refrigerant.

Question 5

An undercharged system will show which of the following gauge readings?

Accepted Answer

An undercharged system will result in lower pressure readings on both the low and high side of the system. Therefore, the correct option is A, which shows low readings on both the low and high side gauges.

Question 6

Restricted airflow through the condenser core will result in higher than normal high-side pressures.

Accepted Answer

When the airflow through the condenser core is restricted, the heat transfer from the refrigerant to the ambient air is reduced, causing the high-side pressure to rise. Therefore, restricted airflow through the condenser core will result in higher than normal high-side pressures.

Question 7

Poor passenger compartment cooling may be the result of dirt or debris plugging the evaporator core cooling fins.

Accepted Answer

Dirt or debris can restrict the airflow through the evaporator core cooling fins, reducing its effectiveness in cooling the passenger compartment.

Question 8

Moisture in a refrigerant system may cause intermittent poor system performance.

Accepted Answer

Moisture in a refrigerant system can result in the formation of ice or frost on the evaporator coils, leading to poor performance of the system. It can also cause corrosion in the system, which can result in leaks and further deterioration of system components. Therefore, it is important to remove moisture from the system during installation and maintenance of the refrigeration system.

Question 9

An R-134a expansion valve system that is properly charged has the following gauge readings,high-side 150 psig and low-side 42 psig and the ambient air temperature is 85°F.Which of the following is the most likely cause?

Accepted Answer

The low-side pressure is lower than it should be, indicating a potential issue with the expansion valve. If it is stuck open, it can cause the low-side pressure to drop too low. Other potential issues would cause both high and low-side pressures to be affected.

Question 10

A pressure gauge reading of 26 psig (179 kPa)inside the evaporator of a system using R-134a means the evaporating temperature of the refrigerant is about

Accepted Answer

The pressure-temperature relationship for refrigerants, including R-134a, allows us to determine the evaporating temperature at a given pressure. A pressure of 26 psig (179 kPa) for R-134a corresponds approximately to an evaporating temperature of 30°F (-1.1°C). This relationship can be found in refrigerant pressure-temperature charts or tables specific to R-134a.

Question 11

On a cycling-clutch system,the desired average temperature of the evaporator should be about 35°F (1.7°C).

Accepted Answer

This is true as the desired temperature for the evaporator of a cycling-clutch system should be maintained at around 35°F (1.7°C) to effectively remove heat from the air conditioning system.

Question 12

Technician A says there is a direct relationship between the pressure and temperature of a refrigerant.Technician B says any apparent temperature-pressure relationships in a contaminated system are not valid.Who is correct?

Accepted Answer

Technician A is correct because according to the basic principles of thermodynamics, specifically the ideal gas law, there is a direct relationship between the pressure and temperature of a gas, which applies to refrigerants in HVAC systems. Technician B is also correct because if a refrigeration system is contaminated, for example with moisture or another gas, the temperature-pressure relationship can be altered, making standard pressure-temperature charts inaccurate for diagnosing or charging the system.

Question 13

A temperature change at the outlet of a system accumulator indicates the accumulator is restricted.

Accepted Answer

A temperature change at the outlet of an accumulator typically indicates a change in the flow rate or a change in the thermal conditions of the fluid, not necessarily a restriction.

Question 14

High-side restrictions can cause extremely high temperatures.

Accepted Answer

High-side restrictions, such as a clogged or restricted condenser, can cause a significant increase in temperature in the high-pressure side of the refrigeration system, leading to overheating and potential damage to the system components.

Question 15

A manifold and gauge set is attached to an operating air conditioner.The low-side gauge reading is too high and the high-side reading is too low.What could be the problem?

Accepted Answer

A defective compressor can cause the low-side pressure to be too high and the high-side pressure to be too low because it is not effectively compressing the refrigerant.

Question 16

If the low-side gauge pressure is showing a vacuum,all of the following defects could be the cause,EXCEPT:

Accepted Answer

Compressor valves being worn would not cause a vacuum on the low-side gauge; instead, it would likely lead to a decrease in system efficiency and cooling capacity. A vacuum on the low-side gauge indicates a restriction or lack of refrigerant flow, which could be caused by a clogged inlet screen, an expansion valve stuck closed, or other blockages, but not by worn compressor valves.

Question 17

Ice on the evaporator coil is often a normal condition.

Accepted Answer

Ice on the evaporator coil is not normal; it indicates issues such as low refrigerant levels, poor airflow, or a malfunctioning component, which prevents the coil from absorbing heat effectively.

Question 18

A refrigerant system with air contamination will still operate properly.

Accepted Answer

Air contamination in a refrigerant system causes inefficiencies, such as reduced cooling capacity and increased power consumption, because air does not condense at the pressures used in refrigeration cycles, leading to improper operation.

Question 19

While a technician is performing an A/C system performance test,it is determined that the low pressure gauge is reading in the vacuum range.This reading could be caused by:

Accepted Answer

A restricted expansion valve can cause the low pressure gauge to read in the vacuum range because it limits the flow of refrigerant into the evaporator, leading to lower pressure on the low side of the system.

Question 20

What could happen if the evaporator pressure becomes too low?

Accepted Answer

If the evaporator pressure becomes too low, moisture in the system can freeze on the evaporator surface, which can restrict air flow and reduce the efficiency of the system. This can lead to a decrease in cooling capacity and potentially cause other issues, such as compressor damage or coil freezing.

Quiz 7: Diagnosis of the Refrigeration System