ASE A7 Heating and Air Conditioning Q & A Part 1

ASE Practice Test Questions & Answers with Explanation

1. When pressure testing the cooling system on a late model vehicle with a gasoline engine, the pressure on the tester drops but no leaks can be found in the engine compartment. Technician A says that there cannot be an internal leak because the engine oil looks normal, not milky like it would be if coolant were present, and there is no white smoke coming from the exhaust pipe. Technician B starts the engine and, seeing the pressure on the tester gauge increase, says that there is an internal leak, a blown head gasket. Who is correct?
A. Technician A only
B. Technician B only
C. Both A and B
D. Neither A or B
The correct answer is B If the engine is started while pressure testing a cooling system and the pressure immediately increases, there could be a head gasket leak, but not into the crankcase. The coolant may be going out the tailpipe, but since this is a late model gasoline engine vehicle and equipped with a catalytic converter, there is no white smoke from the exhaust because the converter super-heats the coolant into such a fine vapor that it is not noticeable.

2. All of the following could cause poor heater performance EXCEPT:
A. Defective temperature blend door actuator
B. Radiator coolant temperature below 150°F
C. Heater core return hose much cooler than inlet hose
D. Stuck open heater control valve
The correct answer is D A stuck open heater control valve could cause problems when heat is not wanted, but because coolant flow to the heater core is not interrupted, the heater valve would not cause poor heater performance. A defective temperature blend door actuator could cause poor heat if the blend door was stuck in the wrong position. Radiator coolant temperature below 150°F would indicate a missing or stuck open thermostat, which could also cause poor heater performance. A heater core return hose that is much cooler than the inlet hose means that the heater core is plugged or air bound, also causing poor heat.

3. The high-side pressure in an A/C system is above specifications. All of the following could cause this problem EXCEPT:
A. A slipping fan belt
B. Overcharged refrigerant
C. A broken compressor reed valve
D. Restricted air flow across the condenser
The correct answer is C A broken compressor reed valve could not cause the high-side pressure to be above specifications.

4. Technician A says that evacuating an A/C system will remove air and moisture from the system. Technician B says that evacuating an A/C system will remove dirt particles from the system. Who is right?
A. Technician A only
B. Technician B only
C. Both A and B
D. Neither A or B
The correct answer is A Evacuating an A/C system removes air and moisture from the system. The receiver/drier may contain a filter or strainer to catch and trap foreign particles and dirt, but this remains in the receiver/drier and is not removed during the evacuation procedure.

5. Technician A says that moisture in an A/C system can freeze in the expansion valve and stop the system from cooling. Technician B says that moisfure in the A/C system will react with R12 to form an acid that can cause corrosion. Who is correct?
A. Technician A only
B. Technician B only
C. Both A and B
D. Neither A or B
The correct answer is C Moisture in the A/C system can ice up in the expansion valve and block refrigerant flow. On systems with Rl2, moisture can combine with the chlorine in the;R12 to form hydrochloric acid. These chemicals can corrode metals and attack rubber parts.

6. When checking recycled refrigerant for excessive air, Technician A says that the container must be stored at 65°F or above for 8 hours out of direct sunlight, before checking the pressure. Technician B says if the pressure is higher than the limit shown for a given temperature, there is air in the tank. Who is correct?
A. Technician A only
B. Technician B only
C. Both A and B
D. Neither A or B
The correct answer is B To purge the air, connect the tank to the recovery/recycling machine and slowly vent the air vapor from the top of the container. Continue venting until the pressure fa!Js below the limit shown on your chart. If the pressure inside the container still exceeds the pressure limit shown, recycle the entire contents. Technician B is wrong because the container must be stored for 12 hours, not eight.

7. At what percentage is refrigerant considered to be pure and safe for recovery?
A. 90%
B. 95%
C. 98%
D. 100%
The correct answer is C Refrigerant is considered pure and safe for recovery if it is at least 98% by weight of a single type of refrigerant. If the refrigerant in the system is less than 98% pure, it should be considered contaminated and reclaimed or destroyed.

8. A blower motor only works on high speed. Which of the following answers are MOST LIKELY?
A. Defective blower relay
B. Defective blower resistor
C. Defective blower switch
D. Blown fuse or tripped circuit breaker
The correct answer is B Answer A is incorrect because a blower relay is generally only used for the high blower speed and this is working. Answer C, the blower switch is a possible cause but the most likely cause for operation on only high speed is that a portion of the resistor assembly is burned out. Answer D is incorrect because if the blower fuse was blown or circuit breaker tripped, the blower would not work at all.

9. During an A/C system performance test, the air temperature at the center outlet duct is warm to
slightly cool and the low and high-side pressures on the manifold gauge set are both low. All: of the following could be the cause of these symptoms EXCEPT:
A. Clogged orifice tube
B. Expansion valve stuck closed
C. Restricted receiver/drier
D. Plugged condenser
The correct answer is D Although the air temperature at the center outlet would be about the same, if the condenser is plugged, the manifold gauge readings would be high. All of the other answers are possible causes for the symptoms in the question.

10. A customer complains of low air flow through the instrument panel duct outlets. Which of the following could be the cause?
A. Faulty blower motor
B. Clogged passenger compartment air filter
C. Stuck mode door
D. All of the above
The correct answer is D A blower motor that does not run on high speed or higher speeds due to a defective relay or resistor would cause reduced air flow. A clogged passenger compartment air filter would create an obstruction and also reduce air flow. Finally, a mode door stuck between two positions would create the impression of reduced air flow because the available air would be routed to two places (i.e., the floor and the dash) instead of one.

11. Recovery/recycling equipment must have shutoff valves located within 12 inches of the hoses service ends so that:
A. Oil can be added to the refrigerant
B. The unit can be isolated from the refrigerant source
C. The filter can be changed without disconnecting the hoses
D. Refrigerant discharge
The correct answer is D Recovery/recycling equipment must have shutoff valves located within 12 inches of the hoses service ends so that refrigerant discharge to the atmosphere can be kept to a minimum. This is according to the Clean Air Act regulations.

12. The blower motor only works on high. Which of the following could be the cause?
A. An open thermal limiter
B. A blown 30 amp fuse
C. An open in circuit 31
D. An open in the P/BK wire between the P/BL and P/BK splice and the blower switch
The correct answer is A An open thermal limiter would prevent the blower motor from working on any speed but high. The other answers are incorrect because any of these causes would prevent the blower motor from working at all.

13. During the diagnosis of an ATC system, a trouble code is obtained that references the blend door
feedback sensor. Technician A says that the sensor should be replaced. Technician B says that the sensor circuit should be tested. Who is correct?
A. Technician A only
B. Technician B only
C. Both A and B
D. Neither A or B
The correct answer is B Fault codes usually only indicate which circuit the problem is in they don’t necessarily indicate which component in the circuit has failed. The problem could be caused by a loose connection, improper modification, or a broken wire, so perform a thorough inspection when diagnosing a malfunction. Ensure that all grounds are dean and making good contact. If basic mechanical and electrical checks fail to locate the problem, follow manufacturer’s electronic system test procedures.

14. The carpet is wet on the passenger’s side of a vehicle. Technician A says this may be caused by a leaking heater core. Technician B says this could be caused by a clogged evaporator case drain tube. Who is correct?
A. Technician A
B. Technician B
C. Both Technicians A and B
D. Neither Technician A or B
The correct answer is C Both Technicians are correct. A leaking heater core will result in coolant leaking on to the passengers carpet. It can result in a sweet smell in the front passenger compartment, therefore Technician A is correct. A clogged drip tube will result in condensation collecting in the evaporator case and dripping into the passenger compartment, therefore Technician B is correct.

15. Technician A says to measure the Sunload Sensor Signal you must use a DVOM and measure its signal voltage changes. Technician B says to use a scan tool and observe the data stream to see the counts change when the light is varied to the sensor. Who is correct?
A. Technician A only
B. Technician B only
C. Both Technician A and B
D. Neither Technician A or B
The correct answer is C The signal can be measured from the Sunload sensor itself be taping into the signal wire coming from the sensor, but it is very hard to do that. The easier way is the use the scan tool and read the input changes in counts as you vary the light being applied to the sensor. However if you are repairing a code, you would go through this procedure to ensure the sensor and circuit is working.

16. When troubleshooting an ATC (Automatic Temperature Control) system, the system responds when the ambient and in-vehicle temperature sensors are heated and cooled. However, there is no response when the sunload sensor is exposed to a light source. Technician A says that the problem is with the sunload sensor. Technician B says that the problem is with the system’s programmer. Who is correct?
A. Technician A only
B. Technician B only
C. Both A and B
D. Neither A or B
The correct answer is A If the system reacts with a change to one or two inputs but not to the third, the problem is most likely confined to the single sensor or its circuit. But if no reaction is observed on any of the units, or only a partial reaction is seen, the problem is usually with the programmer.

17. Vehicles with Dual Zone climate control have a separate ( fill in the blank ) for the passenger side of the vehicle.
A. Mode door
B. Blend door
C. Heater core
D. Evaporator core
The correct answer is B Vehicles with Dual Zone climate control have a separate blend door for the passenger side. The passenger can adjust a separate temperature control, which in turn controls the blend door and the amount of air flowing through the heater core for the passenger side of the vehicle.

18. When filling a container with recycled refrigerant, to what percentage of the container’s gross weight rating should it be filled?
A. 50%
B. 60%
C. 70%
D. 80%
The correct answer is B To prevent overfilling during transfer of refrigerant, never fill a container to more than 60% of its gross weight rating.

19. A vehicle comes into the shop with a complaint of “no cold air”. Technician A says to first turn the key off, set the DVOM to DC volts and measure the voltage present at the electromagnet clutch. If there is no voltage present, replace the compressor. Technician B says set the DVOM to DC volts and measure the continuity of the compressor clutch. Who is correct?
A. Technician A only
B. Technician B only
C. Both Technician A and B
D. Neither Technician A or B
The correct answer is D In the case of Technician A, in order to measure voltage present at the
compressor clutch, the key must be turned on, AC set to a cold AC position and the engine should be running. If there is no voltage present, it would mean there is a problem with the circuit leading to the compressor clutch coil. In the case of Technician B, in order to measure the compressor clutch continuity, the DVOM would need to be set to the Ohm position not the DC volt position.

20. There is a growling or rumbling noise at the A/C compressor when the system is off and the engine is running. The noise stops when the system is turned on. Technician A says that a bad compressor bearing could be the cause. Technician B says that a bad compressor clutch bearing could be the cause. Who is right?
A. Technician A only
B. Technician B only
C. Both A and B
D. Neither A or B
The correct answer is B The compressor clutch bearing allows the rotor/pulley assembly to spin independently of the compressor shaft when the A/C system is off. When the engine is running and the AIC system is off, the compressor clutch bearing is spinning. When the A/C system is turned on, the rotor/pulley assembly and the armature are locked together by the magnetic action of the compressor clutch coil.

21. All of the following could cause lower than normal high-side pressure EXCEPT:
A. Missing air dam
B. Low refrigerant charge
C. Worn compressor
D. Restricted orifice tube
The correct answer is A A lower than normal refrigerant charge and excessive internal wear would both cause the compressor to develop less discharge pressure. A restricted orifice tube would cause refrigerant flow through the system to be slowed. When the refrigerant spends more time in the evaporator, its temperature and pressure are slightly reduced. A missing air dam would cause an air flow problem through the condenser and the radiator. The reduced air flow and possible engine overheating would both cause higher than normal high side pressure.

22. A customer complains of a foul odor coming from the dash outlets whenever the A/C and blower are on. Technician A says that this is caused by a clogged evaporator drain. Technician B says that this is caused by bacterial growth on the evaporator. Who is correct?
A. Technician A only
B. Technician B only
C. Both A and B
D. Neither A or B
The correct answer is C If the drain at the bottom of the evaporator case becomes clogged and water collects and stagnates, or if the surface of the evaporator remains too moist due to high humidity, bacteria can grow in the stagnant water or on the evaporator surface and cause an odor. This odor is then sent into the passenger compartment by the blower motor.

23. The operation of the thermostatic switch depends on the temperature of the:
A. Condenser
B. Compressor
C. Evaporator
D. Outside air
The correct answer is C The thermostatic switch, which is used to cycle the A/C compressor on and off, depends on the temperature of the evaporator in order to operate.

24. A system with a low pressure on the low side and a heavy frost accumulation on the inlet side of the TXV
(Thermostatic Expansion Valve) indicates a:
A. TXV stuck open
B. Clogged condenser
C. Defective compressor
D. Clogged screen or TXV stuck closed
The correct answer is D A low pressure reading on the low side and a heavy frost accumulation on the inlet side of the TXV indicates a clogged screen at the expansion valve inlet or a TXV stuck closed.

25. A typical refrigerant identifier can detect all of the following EXCEPT:
A. R134a
B. HC (hydrocarbons)
C. Air
D. R744
The correct answer is D Systems that use R744 refrigerant, which is pure COz, are still under development. Typical refrigerant identifiers that are currently available can detect Rl2, R134a, R22, air and hydrocarbons.

This post was written by: Martin Hand

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Martin Hand

About Martin Hand

ASE Certified L1 Advanced Mastertech. Martin Hand has over 15 years experience in Asian and European Import Auto Repair. Specializing in electrical diagnosis, engine performance, AT/MT transmission repair/rebuild. Martin is also pursuing a degree in Computers Science & Information Systems starting at Portland Community College while he plans to transfer to OIT. Certified in Java application level programming, experienced with other languages such as PHP, Ruby, JavaScript and Swift. Martin has future plans of automotive diagnostic software development.