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Free ASE School Bus Air Conditioning Systems and Controls (S7) Examination Practice Questions

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Sample Practice Questions

Try these 10 sample questions from the ASE School Bus Air Conditioning Systems and Controls (S7) Examination practice bank. Each includes the answer and explanation. Continue with the interactive practice above to review the full question set.

  1. 1On an A/C system with a sight glass, a continuous stream of bubbles is observed while the system runs. Which condition should the technician investigate first?

    1. A. An insufficient refrigerant charge
    2. B. An excessive refrigerant charge
    3. C. A slipping compressor clutch
    4. D. A dirty evaporator filter

    Answer: A

    Explanation: "A stream of bubbles may indicate a low refrigerant charge, or an obstruction in the system." Bubbles alone do not identify a single fault. Low charge is a supported initial possibility; the other choices are not the indicated sight-glass interpretation in this question.

    Reference: Thermo King Bus Maintenance Manual TK 61949-3-MM-EN — p. 31, Liquid Line Sight Glass

  2. 2On a Thermo King bus A/C system, discharge pressure exceeds the high-pressure cutout setpoint. What should the cutout switch do?

    1. A. Open to stop the compressor
    2. B. Close to raise compressor speed
    3. C. Open to stop only the blower
    4. D. Close to force condenser low speed

    Answer: A

    Explanation: "If the discharge pressure exceeds the switch setpoint, the switch will open to stop the compressor." The switch protects the compressor circuit at excessive discharge pressure.

    Reference: Thermo King Bus Maintenance Manual TK 61949-3-MM-EN — p. 31, High Pressure Cutout Switch

  3. 3A Thermo King bus A/C compressor is inhibited in very cold outside air. Which sensor supplies the relevant outside-temperature measurement?

    1. A. Ambient temperature sensor
    2. B. Return-air temperature sensor
    3. C. Duct-air temperature sensor
    4. D. Floor-air temperature sensor

    Answer: A

    Explanation: "Measures temperature of the ambient air surrounding the bus, protecting the compressor in low ambient temperature." The ATS monitors outside air for low-ambient compressor protection.

    Reference: Thermo King Bus Maintenance Manual TK 61949-3-MM-EN — p. 30, Ambient Temperature Sensor

  4. 4A bus A/C sight glass has a dry-eye indicator that has turned yellow. What condition does this indicate?

    1. A. Normal dry refrigerant
    2. B. Excessive system moisture
    3. C. Excess compressor oil
    4. D. Low condenser airflow

    Answer: B

    Explanation: "The dry eye in the sight glass is GREEN when the system is dry and YELLOW when the system is wet (contains excessive moisture)." Yellow specifically indicates a wet system, so the dry, oil, and airflow interpretations do not match the indicator.

    Reference: Thermo King Bus Maintenance Manual TK 61949-3-MM-EN — p. 31, Liquid Line Sight Glass

  5. 5A bus A/C unit has a suction-pressure transducer installed. Which statement describes the manual's optional low-pressure cutout switch?

    1. A. The separate LPCO switch is not used in that configuration
    2. B. The LPCO is required in series with every transducer
    3. C. The LPCO replaces the discharge-pressure sensor
    4. D. The LPCO must remain closed during all low-pressure faults

    Answer: A

    Explanation: "LPCO not used if suction pressure transducer is installed." The unit configuration determines whether this optional switch is present.

    Reference: Thermo King Bus Maintenance Manual TK 61949-3-MM-EN — p. 31, Low Pressure Cutout Switch

  6. 6Which sensor measures air returning from the bus interior for compartment temperature and humidity control?

    1. A. Return-air temperature sensor
    2. B. Ambient temperature sensor
    3. C. Evaporator coil temperature sensor
    4. D. Water temperature sensor

    Answer: A

    Explanation: "Measures temperature of air returning from the bus interior, regulating the compartment air temperature and humidity." The return-air sensor represents the passenger compartment conditions.

    Reference: Thermo King Bus Maintenance Manual TK 61949-3-MM-EN — p. 30, Return Air Temperature Sensor

  7. 7During a bus A/C performance test, which preparation helps ensure that a pressure comparison is meaningful?

    1. A. Identify the installed system and its components
    2. B. Assume all bus A/C systems use the same controls
    3. C. Use cabin temperature alone as the pressure reference
    4. D. Treat high idle as the full operating range

    Answer: A

    Explanation: "Systems vary greatly. You should be familiar with the system you are working with and be aware of differences among systems." The system must first be identified because its configuration affects how operating pressures are interpreted.

    Reference: Thermo King Bus Maintenance Manual TK 61949-3-MM-EN — p. 69, Analysis Overview

  8. 8When suction pressure drops below the LPCO setpoint on a unit equipped with that switch, which circuit is opened?

    1. A. The compressor clutch circuit
    2. B. The evaporator blower circuit
    3. C. The heater valve circuit
    4. D. The condenser fan high-speed circuit

    Answer: A

    Explanation: "If the suction pressure drops below the switch’s setpoint, the switch opens the compressor clutch circuit, stopping the compressor." The protection device stops compression by interrupting the clutch.

    Reference: Thermo King Bus Maintenance Manual TK 61949-3-MM-EN — p. 31, Low Pressure Cutout Switch

  9. 9A bus controller reduces compressor capacity because the evaporator outlet tube has become too cold. Which sensor provides the input for freeze prevention?

    1. A. Evaporator coil temperature sensor
    2. B. Ambient temperature sensor
    3. C. Floor-air temperature sensor
    4. D. Duct-air temperature sensor

    Answer: A

    Explanation: "If the coil temperature drops too low, the controller reduces the compressor capacity or stops the compressor to prevent the evaporator coil from freezing." The controller acts on the CTS reading to avoid coil freeze-up.

    Reference: Thermo King Bus Maintenance Manual TK 61949-3-MM-EN — p. 30, Evaporator Coil Temperature Sensor

  10. 10A bus A/C system has low suction pressure, a hot liquid line, and a warm suction line. Which fault best fits this combination?

    1. A. Low refrigerant charge
    2. B. High refrigerant charge
    3. C. An expansion valve held wide open
    4. D. Excessive evaporator airflow

    Answer: A

    Explanation: "Low refrigerant charge • Low suction pressure • Hot liquid line • Warm suction line" The combined temperature and pressure observations match the manual's low-charge pattern.

    Reference: Thermo King Bus Maintenance Manual TK 61949-3-MM-EN — p. 71, System Analysis

Topics in this practice bank

These topics describe the available practice for ASE School Bus Air Conditioning Systems and Controls (S7) Examination. Review the examination outline and its sources for scope and allocation details.

  • A/C System Diagnosis and Repair
  • A/C System Component Diagnosis and Repair
    • Compressor and Clutch
    • Evaporator, Condenser, and Related Components
  • Operating Systems and Related Controls Diagnosis and Repair

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These are independent study questions, not actual examination items. For examination requirements and official information, view ASE School Bus Air Conditioning Systems and Controls (S7) Examination details.