ASE A7 Heating Air Conditioning Practice Test
11. A vehicle has an air conditioning system with a variable displacement compressor. It has poor performance at the hottest times of the day. All of the following would result in this condition EXCEPT:
- A. A faulty variable displacement compressor.
- B. A faulty compressor control valve.
- C. A faulty cycling clutch switch.
- D. A low refrigerant charge.
Answer A is wrong. A weak compressor would result in poor performance.
Answer B is wrong. A faulty control valve would affect the air conditioner's performance.
Answer C is correct. A variable displacement compressor eliminates the need for a cycling clutch by altering the compressor's volume based on system demands.
Answer D is wrong. A low refrigerant charge would affect air conditioning performance.
12. A technician is diagnosing a CCOT air conditioning system for poor performance. The compressor's clutch is not cycling and remains engaged whenever the ignition is switched on. Which of the following will result in this condition?
- A. The compressor clutch relay is sticking closed.
- B. A low refrigerant charge.
- C. The compressor clutch relay is sticking open.
- D. An overcharged system.
Answer A is correct. When the relay sticks closed, the compressor's clutch will stay engaged. A relay is a device used to protect control devices like PCMs from the high current used to power devices like an A/C clutch or the radiator fan.
Answer B is wrong. When the relay fails or sticks open, the compressor's clutch will not engage; this is common.
Answer C is wrong. Relays are circuit protection and control devices for sensitive circuits.
Answer D is wrong. A solid-state relay is different than an electromechanical relay. These "silent" relays have no moving parts and are considered more reliable.
13. Technician A says refrigerant enters the evaporator from the bottom inlet tube as a low-pressure liquid. Technician B says the evaporator removes humidity from the air. Who is correct?
- A. Technician A
- B. Technician B
- C. Both A and B
- D. Neither A or B
Answer A is wrong. Refrigerant enters the evaporator from the bottom inlet tube as a low-pressure liquid. As it passes through the core and toward the top, it absorbs heat from the air in the passenger compartment.
Answer B is wrong. The evaporator removes humidity from the air. The more humidity in the air, the more condensation occurs. The moisture collects in the case and flows outside the vehicle through a flexible drip tube.
Answer C is correct. Refrigerant has a low boiling point and changes from a liquid to vapor as it receives heat from the cabin air.
Answer D is wrong. Warm air from the passenger’s compartment cools as it passes through the evaporator’s fins and tubes.
14. A technician is testing the low-pressure sensor's circuit for continuity. The signal wire between the low-pressure sensor and the electronic climate control module is:
- A. Green with a yellow stripe.
- B. Orange with a white stripe.
- C. White with an orange stripe.
- D. Orange with a red stripe.
Answer A is wrong. According to the wiring diagram, there is no green wire with a yellow stripe associated with the low-pressure sensor.
Answer B is correct. The signal wire is orange with awhit e stripe.
Answer C is wrong. The ground wire is white with an orange stripe.
Answer D is wrong. The 5 volt reference wire is orange with a red stripe.
15. A blower motor operates only at high speed. Which of the following is MOST likely causing this condition?
- A. A faulty blower motor.
- B. A low refrigerant charge.
- C. A faulty blower resistor.
- D. A short in the motor's power feed.
Answer A is wrong. A faulty blower motor affects at all selected speeds.
Answer B is wrong. A low refrigerant charge affects performance at all blower speeds.
Answer C is correct. The blower resister's lower speeds share the same power source and offer varying resistance. The high-speed selection is direct and has no resistors.
Answer D is wrong. A short in the motor's power feed would result in little or no operation at all selected speeds.