A7 practice test

An A/C system has a low charge. After evacuating the system, it will not hold a vacuum. This could be caused by a:

(A) pinched A/C line.
(B) restricted filter/drier.
(C) leak in the vacuum reservoir.
(D) leak at the compressor seal.

(D) leak at the compressor seal.
A pinched A/C line and a restricted filter/drier will have no affect on a system's ability to hold a vacuum. The vacuum reservoir stores engine vacuum and if it leaks, it will affect vacuum supply to the air distribution controls. If there is a leak in the refrigeration system, it will not hold a vacuum after being evacuated. A leak at the compressor seal may not allow the system to hold a vacuum. The correct answer is D.

Low side: 75 PSI High side: 375 PSI

A vehicle is being diagnosed for poor A/C performance in stop-and-go traffic. The technician observes the gauge readings shown during a performance test in the service bay. Which of these could be the cause?
(A) Stuck-open thermostatic expansion valve
(B) Inoperative condenser fans
(C) Refrigerant undercharge
(D) Slipping A/C clutch

(B) Inoperative condenser fans
High pressure on both the high-side and low-side of the A/C system can be caused by excess heat due to inoperative condenser fans. The other answers will all result in high-side pressure that is low. The correct answer is B.

During an A/C performance test, the high-side pressure reading is low and the low-side pressure is high when the A/C compressor is engaged. Which of these could be the cause?
(A) A slipping compressor clutch
(B) An overheating engine
(C) A stuck-closed expansion valve
(D) A stuck-open engine thermostat

(A) A slipping compressor clutch
An overheating engine will cause high A/C system pressures. A stuck-closed expansion valve will cause lower than normal low-side and high side pressures. A stuck-open engine thermostat may cause the engine to run cooler but will have little or no affect on the A/C system pressures. If the A/C compressor clutch is slipping, the compressor will be turning slower, resulting in high-side pressures that are low and low-side pressures that are high. The correct answer is A.

The compressor will not engage on the vehicle in the illustration. Technician A says that the refrigerant charge may be too low. Technician B says that an open compressor clutch diode may be the cause. Who is right?
(A) A only
(B) B only
(C) Both A and B
(D) Neither A nor B

(A) A only
The A/C pressure sensor is used by the PCM to prevent A/C compressor operation when the system charge is too low. Technician A's statement is true. An open compressor clutch diode will not prevent the clutch from engaging. Technician B's statement is false. The correct answer is A.

An A/C system is not cooling. On a visual inspection the technician finds that the filter/drier outlet is frosted. Which of these could be the cause?

(A) A system that is undercharged
(B) A stuck-open A/C cycling switch
(C) A restricted filter/drier
(D) A stuck-closed expansion valve

(C) A restricted filter/drier
A restriction in the filter/drier will cause a pressure and temperature drop at that point, causing the filter/drier outlet to frost. An undercharged system will not cause frosting at the filter/drier outlet. A stuck-open A/C cycling switch will prevent compressor operation. A stuck closed expansion valve will cause poor cooling and will not cause a pressure drop at the filter/drier outlet. The correct answer is C.

The blower motor in the illustration operates on HIGH speed only. An open at which of these could be the cause?
(A) W
(B) X
(C) Y
(D) Z

(D) Z
An open at W will prevent current flow to the blower motor when LOW speed is requested. An open at X or Y will cause the blower motor to not operate on any speed. An open at Z will allow only high speed blower motor operation. The correct answer is D.

Low side: -10 PSI High side: 145 PSI

An A/C system's low side is in a vacuum and the high side pressure is low as shown in the illustration. Which of these could be the cause?
(A) Inoperative cooling fans
(B) High system charge
(C) A restriction in the low side
(D) A failed A/C compressor

(C) A restriction in the low side
Explanation: Inoperative cooling fans and a high system charge will cause higher than normal pressures on both sides of the system. A failed compressor will not pull the low side into a vacuum. If there is a restriction in the low side of the system, the compressor will pull that side into a partial vacuum, and since the compressor is starved, there will be low output pressures on the high side causing the readings shown. The correct answer is C.

Low side: 70 PSI High side: 120-140 PSI

During diagnosis, an A/C system has the low side gauge reading shown, and the high side flutters rapidly between 120 PSI and 140 PSI. Which of these could be the cause?
(A) A failed thermostatic fan clutch
(B) A stuck-closed high-pressure sensor
(C) An overcharged system
(D) An internally damaged A/C compressor

(D) An internally damaged A/C compressor
A failed fan clutch will reduce cooling to the condenser and cause high pressure in the discharge side. A failed high pressure sensor will not cause fluctuating high side pressures. An overcharged system will have higher than normal pressures on both sides. Internal compressor damage may cause higher than normal low-side pressures and fluctuating high-side pressures that are lower than normal. The correct answer is D.

The A/C compressor does not function. With the A/C turned ON (circuit activated), the technician observes the meter readings shown. Which of these could be the cause?
(A) An open at W
(B) An open at X
(C) A short to ground at Y
(D) High resistance at Z

(D) High resistance at Z
Ohms law requires that the sum of all voltage drops in a circuit equal the source voltage. DMM 2 shows a voltage drop from the ground side of the relay to ground to be 4.5 volts. Therefore the voltage drop across the contacts of the relay ahead of DMM 2 must be 7.5 volts. This indicates corroded or burned contacts in the relay. The correct answer is D.

An A/C condenser is being replaced on a vehicle that leaked all of the refrigerant from the system during the previous season. Technician A says that the filter/drier may need to be replaced. Technician B says that refrigerant oil may need to be added to the system.

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

(C) Both A and B
Replacing the filter/drier helps restore system integrity by providing good moisture treatment. Technician A's statement is true. Service information should be consulted to determine the correct oil charge procedure and/or quantity when replacing any A/C component. Technician B's statement is true. The correct answer is C.

Which of these will cause an A/C evaporator to freeze?
(A) A clogged evaporator drain
(B) An overcharged A/C system
(C) A stuck-open clutch relay
(D) A stuck-closed A/C cycling switch

(D) A stuck-closed A/C cycling switch
Explanation: A clogged evaporator drain and an overcharged system will not cause the evaporator to freeze. A stuck-open clutch relay will prevent A/C operation. A stuck-closed A/C cycling switch will cause the A/C to run constantly, pulling the evaporator pressures too low and causing it to freeze. The correct answer is D.

The air volume from the HVAC system ducts is too low. Which of these could be the cause?
(A) A stuck recirculation door actuator
(B) A plugged cabin air filter
(C) Low resistance at the fan motor ground
(D) A stuck-open thermostat

(B) A plugged cabin air filter
A stuck recirculation door actuator and a stuck-open thermostat will not affect air volume. Low resistance at the fan motor is a normal condition. A plugged cabin air filter will restrict the air supply and reduce the volume. The correct answer is B.

The heater airflow volume is normal, but the output air is not warm even after the vehicle has been driven for more than 30 minutes. Which of these could be the cause?
(A) A stuck-on radiator cooling fan
(B) An incorrect antifreeze/water ratio
(C) A stuck-closed engine thermostat
(D) An internally clogged heater core

(D) An internally clogged heater core
A stuck-on radiator cooling fan and an incorrect antifreeze-to-water ratio will not significantly affect the heater output temperature. A stuck-closed engine thermostat will cause overheating before the vehicle is driven for 30 minutes. An internally clogged heater core will not allow the circulation of hot engine coolant through the core, reducing the heat output. The correct answer is D.

A vehicle with the schematic shown is being diagnosed for a complaint of the blower motor running at low speed no matter what speed is selected at the switch. This could be caused by an open circuit at:
(A) W.
(B) X.
(C) Y.
(D) Z.

(B) X.
An open at point W will prevent the blower from running. An open at point Y will allow only HI speed operation. An open at point X can cause the symptom because the current will flow through the same resistors as when the fan speed is set to LO. An open at point Z will cause a loss of HI blower only, because the open is before the splice in the ground circuit. The correct answer is B.

After 30 minutes of highway driving on a warm and humid day, a vehicle with a cycling clutch orifice tube stops cooling and the airflow decreases. Which of these could be the cause?
(A) A clogged orifice tube
(B) A stuck-open engine thermostat
(C) Excessive refrigerant oil in the system
(D) A stuck-closed clutch cycling switch

(D) A stuck-closed clutch cycling switch
Explanation: A clogged orifice tube and excessive refrigerant oil in the system will affect A/C cooling all of the time. A stuck-open engine thermostat will not affect A/C cooling. A stuck-closed low pressure cycling switch can cause the evaporator to freeze up that will result in poor cooling and airflow. The correct answer is D.

A vehicle's engine is overheating. During diagnosis, the technician observes that the radiator cooling fan does not operate. The cooling fan is commanded ON with a scan tool and the technician observes system voltage at Y and no voltage at Z. When battery voltage is applied to Z, the radiator cooling fan operates. Which of these could be the cause?
(A) An open relay coil
(B) An open in the PCM driver
(C) An open motor ground
(D) An open relay diode

(B) an open in the PCM driver
Explanation: An open relay coil will result in no voltage at Y. An open motor ground will not allow the fan to run when battery voltage is applied to Z. An open relay diode will not prevent relay operation. The voltage readings obtained at Y and Z when the cooling fan is commanded on with the scan tool indicates that the PCM driver is not grounding the relay coil. The correct answer is B.

The passenger-side temperature cannot be adjusted on a vehicle equipped with a split-distribution front HVAC system. The driver's side operates normally. Which of these could be the cause?
(A) A failed mode door actuator
(B) A failed blend door actuator
(C) A stuck-open recirculation door
(D) A stuck-closed recirculation door

(B) A failed blend door actuator
The mode door directs the flow of air to the defrost, heater, or dash outlets. The recirculation door controls the source of the inlet air. Blend doors control the outlet air temperature. Split distribution HVAC systems use two blend doors and actuators so that the temperature of the driver and passenger zones can be controlled separately. The correct answer is B.

The condenser fan motor runs when the relay in the illustration is bypassed by connecting a jumper wire between W and X. When the pressure switch is bypassed the condenser fan motor does not run, and the technician observes the meter reading shown. Which of these could be the cause?
(A) An open in the relay's control coil
(B) An open in the wiring from point X to the motor
(C) An open condenser fan relay ground
(D) An open condenser fan motor ground

(C) An open condenser fan relay ground
If there is an open in the relay coil the technician will not see the 12.5V reading at Z. An open wire between point X and the condenser fan motor, or an open condenser fan motor ground, will not allow the motor to run when the relay is bypassed. The voltage reading at Z indicates an open condenser fan relay ground. The correct answer is C.

After a cold start, a vehicle's A/C performance diminishes when driven for more than 10 minutes.Technician A says that a sticking temperature blend door could be the cause.Technician B says that a stuck open engine thermostat could be the cause.Who is right?
(A) A only
(B) B only
(C) Both A and B
(D) Neither A nor B

(A) A only
Explanation: Once the vehicle's engine warms up, a sticking temperature blend door may allow unwanted hot air into the cold air mix. Technician A's statement is true. A stuck open engine thermostat will not produce these symptoms. Technician B's statement is false. The correct answer is A.

A vehicle with an automatic temperature control (ATC) system has higher than normal A/C system gauge pressures on both the high and low sides at idle.Technician A says that an electrically open in-car temperature sensor could be the cause.Technician B says that an electrically open coolant temperature sensor could be the cause.Who is right?
(A) A only
(B) B only
(C) Both A and B
(D) Neither A nor B

(D) Neither A nor B
Explanation: An electrically open in-car temperature sensor will prevent the compressor from engaging. Technician A's statement is false. An electrically open coolant temperature sensor may turn on the fans or cause the PCM to disable the compressor clutch depending on the system strategy but, neither one will cause high A/C system gauge pressures. Technician B's statement is false. The correct answer is D.

This question is not like the other questions on the test. It uses the word EXCEPT. Read the question carefully before choosing your answer.An automatic temperature control (ATC) system discharges warm air in the full cold position. Any of these could be the cause EXCEPT:
(A) a open in the compressor clutch circuit.
(B) a stuck-closed recirculation door.
(C) a low refrigerant charge.
(D) an incorrect blend door position.

(B) a stuck-closed recirculation door
Explanation: An open in the compressor clutch circuit or a low refrigerant charge will affect the systems ability to produce cold air. An incorrect blend air door position may produce an air mix that is too warm. A recirculation door that is stuck-closed in either the fresh air or cabin air position will not cause these symptoms. The answer to the question is B.

Which of these will cause an electronic automatic temperature control (EATC) system to be completely inoperative?
(A) A plugged in-car air sampler
(B) A stuck-open hot water valve
(C) A failed microprocessor
(D) An inoperative A/C compressor clutch

(C) A failed microprocessor
A plugged in-car air sampler, a stuck-open hot water valve or an inoperative A/C compressor may cause the system to maintain inaccurate cabin temperature but will not keep the system from functioning. A failed microprocessor, in this case the ATC control unit, is likely to keep the complete system from functioning. The correct answer is C.

The blower motor will not operate at any speed in the illustrated Automatic Temperature Control (ATC) system. The technician connects a DMM to the circuit and the meter readings shown are observed.Technician A says that a blown 40A fuse could be the cause.Technician B says that an open at point X could be the cause.Who is right?
(A) A only
(B) B only
(C) Both A and B
(D) Neither A nor B

(B) B only
Explanation: The DMM reading of 12.5v indicates that the 40A fuse is good. Technician A's statement is false. An open at X will not allow the electronic temperature control module to energize the front blower motor relay. Technician B's statement is true. The correct answer B

Technician A says that refrigerant recovered from one customer's vehicle can be used in another customer's vehicle before being recycled.Technician B says that reclaimed refrigerant may be recharged into an A/C system.Who is right?
(A) A only
(B) B only
(C) Both A and B
(D) Neither A nor B

(B) B only
Explanation: Refrigerant recovered from a vehicle must be recycled before it is used in another customer's vehicle. Technician A's statement is false. Reclaimed refrigerant has been reprocessed by an EPA offsite facility to meet the same standards as new refrigerant. Technician B's statement is true. The correct answer is B.

Technician A says that recycled R-134a refrigerant should be stored in approved containers that are color-coded white.Technician B says that recycled R-134a that contains excess non-condensable gas will cause lower than normal operating pressures if charged into an A/C system.Who is right? (A) A only
(B) B only
(C) Both A and B
(D) Neither A nor B

(D) Neither A nor B
Explanation: Recycled R-134a must be stored in containers that are color-coded light blue. Technician A's statement is false. Excess non-condensable gas in refrigerant may cause higher than normal pressures in the A/C system. Technician B's statement is false. The correct answer is D.