Deck 7: Diagnosis of the Refrigeration System

Question 1

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

Answer 1

True

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?

A) A restricted susction line.
B) A faulty compressor.
C) A restricted expansion vave.
D) Moisture contamination.

Answer 2

B

Question 3

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

A) expansion valve stuck open
B) expansion valve stuck closed
C) compressor valves not sealing
D) compressor clutch inoperative

Answer 3

B

Question 4

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

Question 5

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

A) low side, low; high side, low
B) low side, low; high side, high
C) low side, high; high side, low
D) low side, high; high side, high

Question 6

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.

Question 8

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

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?

A) A restricted receiver drier
B) An out of adjustment temperature blend door
C) A restricted condenser
D) A stuck open expansion valve

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

A) 25°F (-3.9°C).
B) 30°F (-1.1°C).
C) 35°F (1.7°C).
D) 40°F (4.4°C).

Question 11

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

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?

A) Technician A only
B) Technician B only
C) Both A and B
D) Neither A nor B

Question 13

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

Question 14

High-side restrictions can cause extremely high temperatures.

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?

A) refrigerant overcharge
B) insufficient refrigerant
C) defective compressor
D) expansion valve stuck open

Question 16

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

A) clogged inlet screen.
B) expansion valve stuck closed.
C) compressor valves worn.
D) moisture in the system.

Question 17

Ice on the evaporator coil is often a normal condition.

Question 18

A refrigerant system with air contamination will still operate properly.

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:

A) an overcharged refrigerant system.
B) a flooded evaporator
C) a restricted expansion valve
D) service hoses are connected to the incorrect system ports.

Question 20

What could happen if the evaporator pressure becomes too low?

A) Moisture in the system will cause the expansion valve to freeze.
B) Moisture will freeze on the evaporator surface restricting air flow.
C) Liquid refrigerant will damage the compressor.
D) Excessive temperature and pressure extremes will damage the evaporator.

Question 21

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

A) Technician A only
B) Technician B only
C) Both A and B
D) Neither A nor B

Question 22

An R-134a expansion valve system that is properly charged has the following gauge readings,high-side 320 psig and low-side 50 psig and the ambient air temperature is 80°F.Which of the following is the most likely cause? Technician A says an air flow restriction through the condenser coud be the cause.Technician B says the refrigerant system coud be overcharged.Who is correct?

A) Technician A only
B) Technician B only
C) Both A and B
D) Neither A nor B

Question 23

On a properly charged R-134a cycling clutch type A/C system theevaporator is icing.Which of the following could be the cause?

A) Restricted orifice tube
B) Restricted suction side line
C) A faulty pressure cycling switch
D) Moisture contamination.

Question 24

O-ring damage could be caused by

A) overtightening.
B) burrs on the fitting.
C) using the wrong type of O-ring.
D) all of the above.

Question 25

What can a defective compressor cause systems pressures to be?

Question 26

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?

A) Restricted air flow through the condenser.
B) Restricted air flow through the evaporator.
C) A faulty compressor.
D) Moisture contamination.

Question 27

On a vehicle equipped with front and rear A/C dual evaporator system,the front evaporator cools properly,but the rear evaporator is warm.Which of the following is the most likely cause?

A) An overcharged refrigerant system.
B) An undercharged refrigerant system.
C) A stuck open front expansion valve.
D) A stuck open rear expansion valve.

Question 28

What is the primary cause of corrosion in the air-conditioning system?

Question 29

A technician is checking refrigerant system pressures.Both high- and ow-side service ports are located on the A/C compressor.When the compressor is engaged,the high-side pressure instantly goes over 375 psig.What is the most ikely cause of this condition?

A) A resricted expansion valve.
B) A restricted receiver dryer.
C) A faulty cooling fan.
D) A restricted discharge hose.

Question 30

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?

A) Technician A only
B) Technician B only
C) Both A and B
D) Neither A nor B

Question 31

What is one method for determining if the internally regulated thermostatic expansion valve is functioning correctly?

Question 32

What are the possible causes of a low-side pressure that is high (45 psig),and a high-side pressure that is low (150 psig)?

Question 33

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

A) Compressor cycles rapidly when equipped with a cycling-clutch pressure switch
B) Higher than normal high-side pressures
C) Reduced cooling capacity under any load condition
D) Early compressor failure

Question 34

At highway speed the A/C system cools normally,but poorly during around town stop and go driving.What is the most likely case of this condition?

A) A stuck closed engine thermostat.
B) A misadjusted air blend door.
C) An open electronic cooling fan relay.
D) An open high-speed blower relay.

Question 35

What is the real hazard of excessive concentrations of refrigerants in the service area,whether or not they have contacted an open flame?

Question 36

When can R-134a be used in a R-12 system?

Question 37

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?

A) Technician A only
B) Technician B only
C) Both A and B
D) Neither A nor B

Question 38

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?

A) A restriction on the high side of the refrigerant system.
B) Low refrigerant levels.
C) Normal refrigerant system operation.
D) Faulty refrigerant compressor

Question 39

What may happen if the expansion valve remote bulb is not making contact with the evaporator outlet tube?

Question 40

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

A) Technician A only
B) Technician B only
C) Both A and B
D) Neither A nor B

Question 41

What effect would an overcharge with refrigerant oil have on a system and how would it be detected?

Question 42

What is the symptom of a refrigerant system that is overcharges with refrigerant?

Question 43

What should you do first before condemning a refrigerant system component?

Question 44

If a refrigerant system is contaminated with moisture what would you expect to see on the low-side and high-side guages?

Question 45

If the refrigerant inside the evaporator is several degrees below 32°F (0°C),what keeps the evaporator from icing?

Question 46

List the probable causes of high pressure on both the low and high sides of an operating air conditioning system.

Question 47

How is a baseline used in a refrigerant system diagnosis test?

Question 48

How does the technician determine whether an excessively low gauge reading is caused by a clogged screen or by moisture in the system?

Question 49

Name some ways in which air could enter the air conditioning system.

Question 50

What effect would a high-side restriction have on a system and how would it be detected?

Question 51

What effect would a low-side restriction have on a system and how would it be detected?

Question 52

What are most restrictions in a refrigerant system are caused by?

Question 53

By comparison what are the different pressure characteristics of R-134a refrigerant compared to R-12 refrigerant?