UNIT 4 EX A/C

An air-conditioning system should be pumped down (evacuated) for a minimum of ____ minutes.

30

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?

A faulty compressor clutch.

On a properly charged R-134a cycling clutch type A/C system the evaporator is icing. Which of the following is most likely the cause?

A faulty pressure cycling switch

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?

A stuck open expansion valve

An inoperative cooling fan may cause high lead (high-side) pressure at what vehicle speeds?

Both

Charging the system is being discussed. Technician A says that the refrigerant must be weighed (or metered) to obtain a proper charge. Technician B says that overcharging the system will reduce its cooling efficiency. Who is correct?

Both

Dye leak detectors are being discussed. Technician A says that injection dye will be visible after a few days of system operation if a small leak is present. Technician B says that a special lamp is required to locate a small leak with fluorescent dye. Who is correct?

Both

Refrigerant analyzers or identifiers are being discussed. Technician A says that if the analyzer displays "R-134a," then the refrigerant is 98 percent pure. Technician B says that if "HC" is displayed, then the refrigerant is flammable. Who is correct?

Both

Technician A says that at point "A" the refrigerant should be a low-pressure gas. Technician B says that at point "B" the refrigerant should be a low-pressure liquid. Who is correct?

Both

Technician A says that the A/C system may be charged through the LOW side when the system is operating. Technician B says that the A/C system may be charged through the HIGH side when the system is off . Who is correct?

Both

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

Both

Technician A says the Delta T method of adjusting the charge levels of the refrigerant system relies on a comparison of the inlet and outlet temperatures of the evaporator. Technician B says systems should always be checked first for refrigerant contamination. Who is correct?

Both

Technician A says the manifold and gauge set is an important diagnostic tool. Technician B says the manifold and gauge set is an important tool for evacuating and charging the system. Who is correct?

Both

Which of the following is NOT a symptom of an overcharged air conditioning system?

Compressor cycles rapidly when equipped with a cycling-clutch pressure switch

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

F

Ice on the evaporator coil is often a normal condition.

F

System malfunctions cannot be detected by visual inspection.

F

When the air-conditioning system is operating, the suction line should feel hot to the touch.

F

When making system repairs, install the receiver-dryer or accumulator

Last

During a refrigerant system performance test the following results are recorded: outside ambient temperature of 90°F, high-side gauge reading of 145 psi, and low-pressure gauge reading of 14 psi. What is indicated by these results?

Low refrigerant levels

What could happen if the evaporator pressure becomes too low?

Moisture will freeze on the evaporator surface, restricting air flow.

A technician determined that all of the refrigerant had leaked out of the A/C system. Technician A says that the low-pressure switch will need to be replaced before the system can be recharged. Technician B says that the low-pressure switch will need to be adjusted before the system can be recharged. Who is correct?

Neither

Technician A says that a restriction at point "A" would cause high high-side pressure and low low-side pressure. Technician B says that a restriction at "B" would cause low high-side pressure and low low-side pressure. Who is correct?

Neither

Technician A says that any kind of refrigerant can be added to the system for leak testing. Technician B says that it is not necessary to purge the hose between the refrigerant container and gauge manifold when adding refrigerant for leak testing. Who is correct?

Neither

Most original equipment manufacturers use what type of lubricant in their R-134a systems?

PAG

On a properly charged R-134a system an A/C performance test indicates both normal high- and low-side pressures, but poor cooling. Which of the following is the most likely cause?

Restricted air flow through the evaporator

A leak may be marked by the presence of refrigeration oil.

T

High-side restrictions can cause extremely high temperatures.

T

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

T

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

T

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

T

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

T

When the air-conditioning system is operating, the discharge line should feel hot to the touch.

T

During routine equipment inspection, a technician notices that the R-134a recovery tank pressure is 115 psig at an ambient tank temperature of 85°F. Using the chart above what should the technician conclude?

Tank pressure is high and contaminated with noncondensable gas.

On a refrigerant system there is heavy frost on the expansion valve inlet and low-side pressure is well below normal. Technician A says that the expansion valve stuck in the open position could be the cause. Technician B says that a restricted expansion valve inlet screen could be the cause. Who is correct?

Tech A

Technician A says recycled refrigerant in portable storage containers should be periodically checked for noncondensable gas contamination. Technician B says contaminated refrigerant will not affect system performance. Who is correct?

Tech A

Technician A says that the performance test is a way of measuring system pressures. Technician B says that the performance test is a way of measuring the outside humidity. Who is correct?

Tech A

Technician A says the pressures shown in the figure may indicate excessive moisture in the system. Technician B says the pressures indicate a possible defective metering device. Who is correct?

Tech A

A technician is checking the evaporator for leaks on an R-134a refrigerant system. Technician A says that it is acceptable to use shop air to pressurize the system and use an electronic microphone to listen for leakage. Technician B says that it is acceptable to charge the system with R-134a and then insert the electronic leak detector probe in the evaporator drain. Who is correct?

Tech B

Technician A says that a soap solution must only be used in well-ventilated spaces only. Technician B says that leaks often occur in areas of limited access, where it is difficult to use a halogen leak detector. Who is correct?

Tech B

Technician A says that the evacuation process will remove dirt and debris from the refrigerant system. Technician B says that the evacuation process will remove moisture and air from the refrigerant system. Who is correct?

Tech B

Technician A says that the electronic leak detector probe should be held directly against a suspected leak area during a leak test. Technician B says that the electronic leak detector requires routine calibration and probe tip inspection and maintenance. Who is correct?

Technician B only

A fluorescent leak detector will work only after a special dye is injected into the system.

True

An R-134a system is more likely to absorb moisture than an R-12 system.

True

The electronic (halogen) leak detector is the most expensive and sensitive of all leak detection devices.

True

All of the following statements about system evacuation are true, EXCEPT:

Vacuum pump efficiency is increased at higher altitudes.

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:

a restricted expansion valve

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

compressor valves worn.

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?

defective compressor

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

expansion valve stuck closed

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

low side, low; high side, low

All of the following statements about injecting a dye solution into the air-conditioning system are true, EXCEPT:

the dye affects the overall performance of the system.