ASE A7 Heating Air Conditioning Practice Test
16. The compressor's clutch squeals whenever the clutch is engaged. The compressor's clutch coil is being tested for resistance. There are 12 volts at the connector, and the ground is good. The resistance of the coil is 0.00 Ohms. Which of the following is correct?
- A. The clutch coil has an open in its windings.
- B. The clutch coil has a short in the windings.
- C. Both A and B.
- D. Neither A or B.
Answer A is wrong. A reading of infinity indicates an open in the windings. Typically, the resistance of an A/C clutch coil is ~ 2 - 5 Ohms.
Answer B is correct. A reading of 0.00 Ohms indicates a short in the coil windings.
Answer C is wrong. An A/C compressor clutch coil is a simple device made of fine wire windings wrapped into a coil.
Answer D is wrong. When current is passed through the coil, it creates a strong magnetic field that pulls a splined hub into contact with the spinning pulley. This action engages the compressor.
17. A vehicle's air conditioning system blows warm air only while the vehicle is stopped or sitting idle. The air conditioning system performs well under all other conditions. All of the following would result in this condition EXCEPT:
- A. Debris on the condenser's fins.
- B. A faulty electric fan motor.
- C. A frozen thermostatic expansion valve.
- D. An overheating engine.
Answer A is wrong. Debris on the condenser's fins reduces the ability of the condenser to transfer heat. This restriction to airflow is more pronounced when the vehicle is at rest.
Answer B is wrong. While the vehicle travels forward, ram air passes through the condenser. While at rest, a weak fan motor is not pulling enough air through the condenser, resulting in a loss of heat transfer.
Answer C is correct. This is an EXCEPT type question. The refrigerant flow is restricted once the expansion valve freezes. The air conditioner will perform poorly at all speeds.
Answer D is wrong. Excessive engine heat affects the condenser's ability to transfer heat to the atmosphere.
18. The carpeting is wet on the passenger's side of the vehicle. Which of the following statements is correct?
- A. A flooded evaporator core results in this condition.
- B. A leaking heater core results in this condition.
- C. A clogged receiver drier results in this condition.
- D. A faulty expansion valve results in this condition.
Answer A is wrong. A flooded evaporator core affects air conditioning performance and can damage the compressor but does not leak fluid onto the passenger's carpet.
Answer B is correct. If a leak occurs in the heater core, the coolant leaks onto the vehicle's front floorboard. It may also drip out of the case's flexible drip tube and be seen on the shop floor or the customer's driveway.
Answer C is wrong. A clogged receiver drier causes a restriction in the system; frost typically appears around restrictions in air conditioning components.
Answer D is wrong. A faulty expansion valve affects system performance but does not leak fluid onto the passenger's carpet.
19. Technician A says the in-cabin temperature sensor is an (NTC) negative temperature coefficient sensor. Technician B says to use an ohmmeter to test the in-cabin temperature sensor for resistance. Who is correct?
- A. Technician A
- B. Technician B
- C. Both A and B
- D. Neither A or B
Answer A is wrong. The in-cabin or in-car temperature sensor is an NTC or negative temperature coefficient sensor that can be tested for resistance with an ohmmeter.
Answer B is wrong. The electronic automatic temperature control system's microprocessor uses this, along with the ambient temperature and sun load sensors input, to adjust cooling load, fan speed, and volume according to different temperatures and conditions.
Answer C is correct. Both technicians are correct.
Answer D is wrong. It senses the air temperature of the passenger compartment. Many sensors contain a small electric fan that can fail, resulting in an inaccurate sample.
20. A vehicle with a (TXV) thermostatic expansion valve air conditioning system blows cold air for several minutes and then goes warm. Which of the following is MOST likely causing this condition?
- A. A low refrigerant charge.
- B. Moisture in the system.
- C. A leaking evaporator core.
- D. A faulty compressor.
Answer A is wrong. A low refrigerant charge results in reduced air conditioning performance at all times.
Answer B is correct. After a few minutes, the moisture freezes in the expansion valve, restricting refrigerant from entering the evaporator core. A saturated receiver drier will result in this condition.
Answer C is wrong. A leaking evaporator core produces a low refrigerant charge. A low refrigerant charge results in reduced air conditioning performance at all times.
Answer D is wrong. A faulty compressor results in low discharge pressure.