Free ASE Transit Bus Heating, Ventilation, and Air Conditioning (H7) Practice Questions

Sample Practice Questions

Try these 10 sample questions from the ASE Transit Bus Heating, Ventilation, and Air Conditioning (H7) practice bank. Each includes the answer and explanation. Continue with the interactive practice above to review the full question set.

1. 1Why does pulling a vacuum help remove moisture from a bus A/C system before charging?

   1. A.It lowers the boiling point, causing water to condense.
   2. B.It lowers the boiling point, allowing water to vaporize.Correct answer: B
   3. C.It raises the boiling point, causing water to condense.
   4. D.It raises the boiling point, allowing water to vaporize.

   Explanation: The instruction states, "A vacuum pulled on the system will result in reducing the boiling point of water to a level where it changes to a vapor at ambient temperatures". Lower pressure permits evaporation at ambient temperature; the pump removes vapor. Condensation and an increased boiling point reverse parts of this mechanism.

   Reference: Trans/Air Evacuation Work Instruction (INS-940) — p. 1, Evacuation

2. 2A bus's coolant-fed heating circuit has been drained and refilled. What additional service does the Prevost heating procedure require before treating the refill as complete?

   1. A.Leave the heater isolation valves closed during the final check.
   2. B.Top up the surge tank without venting the heater cores.
   3. C.Bleed trapped air from the heating circuit.Correct answer: C
   4. D.Stop the circulating pump and accept reservoir level alone.

   Explanation: The procedure states, "Whenever the heating system has been drained and refilled, or the system has run low on coolant and coolant has been added, it is necessary to bleed air from heating system." Refilling alone does not establish that the long heating lines are air-free.

   Reference: Prevost Maintenance Manual PA1621, Section 22: Heating and Air Conditioning — p. 55, §6.4.5 Bleeding Heating System

3. 3An EC4.0 controller shows a low-voltage Lu fault after voltage between terminals 8 and 10 falls below 12 Vdc. Which output behavior is specified?

   1. A.All evaporator, condenser, and compressor relays stay on.
   2. B.The compressor stays on while both fan outputs shut off.
   3. C.The evaporator shuts off while the compressor relay stays on.
   4. D.Compressor and condenser relays turn off; the evaporator stays on.Correct answer: D

   Explanation: The low-voltage section says EC4.0 will "de-energize the compressor clutch and condenser relays" and adds, "Note the evaporator relay remains energized." Continuing evaporator operation therefore does not rule out the specified low-voltage shutdown.

   Reference: Trans/Air EC4.0 Electronic Climate Control System Service Manual — p. 4, Low System Voltage

4. 4During an INS-940 evacuation check, pressure rises above 1000 microns after the pump is isolated, then levels off. What does this pattern most likely indicate?

   1. A.A dry system; the specified vacuum-hold test has passed.
   2. B.A system leak; stop evacuation and repair the leak.
   3. C.Residual air; introduce refrigerant now to displace it.
   4. D.Residual moisture; reconnect the pump and keep evacuating.Correct answer: D

   Explanation: INS-940 states, "A system that rises above 1000 microns but levels off and stabilizes when the pump is isolated is probably still contaminated with moisture." It directs continued evacuation. A dry circuit must hold below 1000 microns; an ongoing non-stabilizing rise is the separate leak pattern. Introducing charge does not replace removing residual air and moisture.

   Reference: Trans/Air Evacuation Work Instruction (INS-940) — p. 3, isolated-pump vacuum assessment

5. 5Under the Prevost heating-system filling procedure, how should the heater shutoff valves and circulating pump be set after the initial fill?

   1. A.Open the shutoff valves and energize the circulating pump.Correct answer: A
   2. B.Close the shutoff valves and energize the circulating pump.
   3. C.Open the shutoff valves and electrically isolate the pump.
   4. D.Close the shutoff valves and electrically isolate the pump.

   Explanation: The procedure states, "After initial filling, the hot water shutoff valves should be open and the water circulating pump should be energized to assist in circulating coolant through the heating system." Both an open path and pump operation are part of the prescribed filling arrangement.

   Reference: Prevost Maintenance Manual PA1621, Section 22: Heating and Air Conditioning — p. 55, §6.4.4 Filling Heating System, step 3

6. 6An EC4.0 continuously displays Sr for two minutes during a cooling request, while compressor and condenser relays remain off. Which condition can explain this documented pattern?

   1. A.The 1000-hour service reminder alone.
   2. B.Both pressure switches open, or a safety-circuit fault.Correct answer: B
   3. C.The normal compressor restart lockout.
   4. D.A shorted cabin-temperature sensor cable.

   Explanation: The manual states, "If both high and low pressure switches open or there is a circuit fault," the controller displays Sr and de-energizes the clutch/condenser relays. The service reminder is intermittent, the ordinary restart lockout is 30 seconds, and the sensor-short troubleshooting branch displays Lo. Those do not match a continuous two-minute Sr shutdown.

   Reference: Trans/Air EC4.0 Electronic Climate Control System Service Manual — p. 4, Safety & Fault Protection—Sr circuit fault

7. 7A Trans/Air system's vacuum rises above 1000 microns and continues rising without stabilizing after pump isolation. Under INS-940, what is required before proceeding with charging?

   1. A.Locate and repair the leak, then repeat evacuation.Correct answer: A
   2. B.Add refrigerant until the vacuum reading stabilizes.
   3. C.Add compressor oil until the pressure stops rising.
   4. D.Accept the reading because pump isolation causes it.

   Explanation: INS-940 states, "A system that rises above 1000 microns and continues to rise without stabilizing has a system leak that must be repaired before continuing". The following direction is to repeat the evacuation steps after correcting the leak. Adding oil or refrigerant does not satisfy this requirement.

   Reference: Trans/Air Evacuation Work Instruction (INS-940) — p. 3, isolated-pump vacuum assessment

8. 8A coolant valve with a pneumatic pilot fails to close. Supply air meets its nameplate minimum while idle but drops below that minimum as the valve operates. What is the relevant fault under the Prevost valve troubleshooting procedure?

   1. A.The nameplate minimum applies only with the pilot inactive.
   2. B.The idle pressure reading rules out an air-supply problem.
   3. C.The pressure drop proves that the pilot supply is excessive.
   4. D.The pilot air supply cannot maintain the required operating pressure.Correct answer: D

   Explanation: For a valve that fails to close, the procedure specifies pilot pressure at least equal to the nameplate minimum and states, "It should not go below minimum while valve is operating." An idle-only pressure result does not meet that loaded operating requirement.

   Reference: Prevost Maintenance Manual PA1621, Section 22: Heating and Air Conditioning — p. 38, §4.12.1 Valve Troubleshooting—Valve fails to close

9. 9An EC4.0 relay board powers up, but the condenser circuit has no supply voltage. Which terminal is the dedicated condenser power input?

   1. A.Terminal 11.Correct answer: A
   2. B.Terminal 3.
   3. C.Terminal 8.
   4. D.Terminal 10.

   Explanation: Table 2 identifies terminal 11 as "Condenser Power Input". Terminal 3 is the ignition input, terminal 8 supplies evaporator/compressor/heat circuits, and terminal 10 is ground. Board power alone does not verify the separate condenser feed.

   Reference: Trans/Air EC4.0 Electronic Climate Control System Service Manual — p. 2, Table 2 Terminal Strip Positions—terminal 11

10. 10An INS-940 evacuation produces an immediate micron-reading drop rather than a gradual reduction. What should the technician do before accepting that reading?

    1. A.Accept the quick reading as a complete system evacuation.
    2. B.Start charging without an isolated-pump vacuum assessment.
    3. C.Check whether couplers actually depress the Schrader valves.Correct answer: C
    4. D.Continue for a preset time without checking system access.

    Explanation: The instruction says, "If the micron level immediately drops, check the couplers (2 & 3) to be sure the schrader valves are depressed at the suction and discharge accesses." The pump may not have proper access to the circuit. Neither a quick reading nor elapsed time establishes that access or replaces the prescribed vacuum assessment.

    Reference: Trans/Air Evacuation Work Instruction (INS-940) — p. 2, evacuation step 9