ASE A7 Heating Air Conditioning Practice Test

Diagram of automotive ac control circuit.

41. Component A in the electrical diagram above has all of the following characteristics EXCEPT:

  • A. It is a Negative Temperature Coefficient sensor.
  • B. It is a thermistor.
  • C. It is a variable resistor.
  • D. It is a switch.


ECT sensor

Answer A is wrong. An ECT sensor is an (NTC) Negative Temperature Coefficient sensor.

Answer B is wrong. An engine coolant temperature sensor is a thermistor.

Answer C is wrong. An engine coolant temperature sensor is a variable resistor that modifies a 5 volt reference signal from the control module.

Answer D is correct. It's a sensor, A/C systems use switches that are either open or closed. They don't modify reference signals like sensor's do.

42. A frozen spot is noticed in the center of the condenser. Technician A says a frozen spot on a component or connection indicates a restriction in the system. Technician B says this is caused by a clogged orifice tube. Who is correct?

  • A. Technician A
  • B. Technician B
  • C. Both A and B
  • D. Neither A or B


Answer A is correct. A restriction in a line or component acts like a metering device and changes the system's pressure. The change in pressure results in a change in temperature.

Answer B is wrong. A clogged orifice tube will result in a frozen spot on the line containing the fixed orifice tube.

Answer C is wrong. Technician A is correct.

Answer D is wrong. Technician A is correct.

43. A technician is diagnosing a vehicle's air conditioning system. The vehicle has good engine performance, but the air conditioner is blowing warm air only. A yellow substance is noticed around the evaporator case drip tube. Technician A says this is coolant leaking from the heater core. Technician B says this is fluorescent dye leaking from the evaporator core. Which technician is MOST likely correct?

  • A. Technician A
  • B. Technician B
  • C. Both A and B
  • D. Neither A or B


Answer A is wrong. It could be coolant leaking from the heater, but is more likely dye leaking from the evaporator, because poor air conditioning is the original complaint. Both possibilities should be inspected further. Visually inspect the coolant reservoir for low coolant level.

Answer B is correct. Dye is injected into a system with hard to find leaks. Note that a R-12 system uses one type of dye and a R-134a system uses another. The dye used with R-134a shows up fluorescent yellow. This is brought to light with a special light and glasses.

Answer C is wrong. Technician B is correct.

Answer D is wrong. Technician B is correct.

44. R 134a Refrigerant:

  • A. Changes from a vapor to a liquid as it absorbs heat.
  • B. Containers are sky blue colored.
  • C. Has a very high boiling point.
  • D. Is a CFC that contains chlorine.


Answer A is wrong. R134a changes from a liquid to a vapor as it receives heat energy and boils in the evaporator. The heat energy is then carried to the condenser to be released into the atmosphere through another heat transfer process.

Answer B is correct. An R134a refrigerant system has less refrigerant capacity than a similar R12 system. They also have different pressure characteristics. R134a is contained in a sky blue container, R-12 is contained in a white container.

Answer C is wrong. R134a has a very low boiling point.

Answer D is wrong. R134a refrigerant is an HFC containing hydrogen, fluorine, and carbon, but no chlorine. Chlorine is contained in R12 and is considered harmful to the ozone layer. It should be noted that HFC's contribute to global warming and must be contained.

45. A cooling system is loosing coolant. A pressure test has been performed and no leaks were found. Which of the following is MOST likely causing this condition?

  • A. Leaking water pump.
  • B. Faulty radiator pressure cap.
  • C. Leaking heater core.
  • D. Leaking radiator.


Answer A is wrong. No external leaks were found. The radiator cap should be pressure tested.

Answer B is correct. A faulty radiator cap will allow coolant to leak past its seal and overflow from the recovery system.

Answer C is wrong. Answer B is correct.

Answer D is wrong. Answer B is correct.