ASE A7 Heating Air Conditioning

A vehicle has poor air conditioning performance. The customer has added R134a refrigerant to the system. Technician A says to use a refrigerant identifier. Technician B says refrigerant mixtures are not recommended, but will not affect system pressures. Who is correct?

Answer A is correct. Use a refrigerant identifier to identify R12, R134a, R22, hydrocarbons and air.

A vehicle's air conditioning performance is reduced at low speeds and stop lights, but cools at highway speeds. Which of these is MOST likely the cause of this condition? A. A low refrigerant charge. B. A missing fan shroud. C. A normal condition. D. A faulty compressor clutch relay.

Answer B is correct. A properly fitting and fastened fan shroud is vital for good A/C and engine performance. Many of these shrouds and dams create a low pressure area behind the radiator and condenser. Loose or missing shrouds will be especially noticeable as the vehicle slows and ram air is reduced.

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 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.

An air conditioning system with a variable displacement compressor has poor performance in high demand situations. All of these could be the cause EXCEPT: A. A low refrigerant charge. B. A faulty control valve. C. A faulty low pressure switch. D. A weak compressor.

Answer C is correct. A variable displacement compressor uses a control valve to alter system pressures. A cycling clutch orifice tube system has a pressure cycling switch on the low side of the system, often located on the accumulator.

A manifold gauge indicates a system has low discharge pressure. The MOST likely cause of this condition is: A. A restricted condenser. B. A loose fan belt. C. A damaged compressor reed valve. D. A broken compressor piston.

Answer C is correct. Damaged reed valves or plates result in low discharge pressure.

A vehicle's air conditioner blows cold air at normal speeds, but warm air while sitting at stop lights. The LEAST likely cause of this condition is: A. An overheating engine. B. A weak electric fan motor. C. A frozen expansion valve. D. Debris in the condenser fins.

Answer C is correct. This is a least likely type question. Once the expansion valve freezes, the air conditioning would have poor performance at all speeds.

All these statements are true about a throttle position sensor EXCEPT: A. It indicates throttle position to the engine control module. B. The control module disengages the A/C clutch at wide open throttle. C. The ECM disengages the A/C clutch at idle. D. The throttle position sensor signal is used to indicate throttle angle.

Answer C is correct. This is an except question. All the other choices are true except this one. The compressor's clutch is not disengaged at idle, it's disengaged at WOT providing additional power when needed.

During a performance test on a CCOT system the manifold gauge indicates that the high side pressure is low and the low side pressure is high. This is caused by a: A. Stuck open expansion valve. B. Frozen expansion valve. C. Restricted condenser. D. Faulty compressor.

Answer D is correct. A high low side and a low high side indicates a faulty A/C compressor.

During an initial inspection, the technician notices that one line on the receiver drier is cooler than the other. This is caused by: A. Nothing it's a normal condition. B. A low refrigerant charge. C. Too much oil in the system. D. A restriction in the receiver drier.

Answer D is correct. A restriction in the receiver drier will result in a change in line temperatures. This is because one of the properties of refrigerant is that it changes temperature along with pressure. The restriction has altered pressure in the drier and lowered the temperature of the outlet line.

All of these are true about an accumulator EXCEPT: A. It is located on the low side of the system. B. It prevents excess liquid from entering the compressor. C. It contains a desiccant capable of absorbing moisture from the refrigerant. D. This system contains a thermostatic expansion valve to meter the refrigerant.

Answer D is correct. An accumulator is used on a CCOT or Cycling Clutch Orifice Tube type system.

All of these are true about an air conditioner's evaporator EXCEPT: A. It removes humidity from the air. B. Refrigerant flows from the bottom to the top. C. Refrigerant enters the evaporator as a liquid. D. The refrigerant changes from a vapor to a liquid as it receives heat from the cabin air.

Answer D is correct. The refrigerant converts from a liquid to a vapor, because it boils as it receives heat from the cabin air. Refrigerant has a very low boiling point.

An air conditioning system contains a thermostatic expansion valve. The suction line leading to the compressor is cool to the touch. This indicates: A. A stuck open expansion valve. B. A low refrigerant charge. C. A stuck closed expansion valve. D. A normal condition.

Answer D is correct. This is a normal condition.

Two technicians are discussing electric cooling fans and air conditioning performance. Technician A says electric fans regulate refrigerant temperatures more precisely than belt driven fans do. Technician B says electric cooling fans are controlled by control modules that use temperature and pressure actuated sensors and switches. Who is correct?

BOTH TECH A AND TECH B. Electric fans offer more precise control than the conventional belt driven fans do. They're important for engine cooling, air conditioning and heater performance. These fans are controlled by a control module that uses pressure and temperature actuated sensors and switches.

The carpet is wet on the passenger's side of a vehicle. Technician A says this may be caused by a leaking heater core. Technician B says this could be caused by a clogged evaporator case drain tube. Who is correct?

Both technicians are correct

A gurgling sound is heard coming from inside the dashboard of a vehicle. Technician A says this is air trapped in the heater core. Technician B says this noise can be caused by a blown head gasket. Who is correct?

Both technicians are correct.

An EATC air conditioning system has low fan speed operation during high demand situations, like in direct sunlight. Technician A says this is because something is covering the sun load sensor's photo diode. Technician B says a sun load sensor is a variable resistor and can be tested with an ohmmeter. Who is correct?

Both technicians are correct.

Technician A says refrigerant flows from the top of the condenser to the bottom. Technician B says a restriction in a condenser can cause damage to the compressor. Who is correct?

Both technicians are correct.

The compressor is rapidly cycling on and off on a CCOT air conditioning system. Technician A says this condition can be caused by a low refrigerant charge. Technician B says this could be caused by a faulty clutch cycling switch. Who is correct?

Both technicians are correct.

The in-cabin temperature sensor is suspected for an air conditioner's poor performance. Technician A says the in-cabin temperature sensor is a NTC that should be tested for resistance with an ohmmeter. Technician B says the aspirator may be disconnected from the vent system. Who is correct?

Both technicians are correct.

Two technicians are discussing refrigerant storage. Technician A says HFC-134a is contained in a sky blue container. Technician B says CFC-12 is contained in a white container. Who is correct?

Both technicians are correct. (HFC-134a) R-134a is stored in a sky blue container with a sky blue label, and (CFC-12) R-12 is stored in a white container with a white label. Each refrigerant has its own color assignment. R-12's assignment is white and R-134a is sky blue "light blue".

An air conditioning system blows only warm air when the heater is on high output. Technician A says this could be a faulty heater control valve. Technician B says this could be caused by the cooling system's thermostat. Who is correct?

Both technicians are correct. A restricted heater control valve will leave a vehicle with low heater performance. A stuck open thermostat has a negative effect on the heater's performance.

Technician A says the expansion valve is located on the inlet port of the evaporator. Technician B says the expansion valve's temperature sensing bulb is located near the outlet port of the evaporator. Who is correct?

Both technicians are correct.An expansion valve is at the inlet port of the evaporator and the sensing bulb is placed on the outlet port.

An air conditioner with an expansion valve performs poorly only during the hottest times of the day. Technician A says the receiver drier may be saturated. Technician B says there may be moisture in the refrigerant. Who is correct?

Both technicians are correct.The receiver drier contains a desiccant that must be changed after it's been exposed to moisture. If saturated with moisture, the excessive moisture in the drier will flow to the expansion valve and freeze, reducing system performance. Poor system performance is most noticeable during the hottest times of the day.

A squeal is heard only when the compressor clutch first engages. Technician A says this is caused by a loose serpentine belt. Technician B says this is caused by a worn clutch pulley bearing. Who is correct?

TECH A is correct. A loose serpentine belt will cause a squeal when the clutch first engages.

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?

TECH 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.

Two technicians are discussing an inoperative electric blend door in an automatic air conditioning system. Technician A says to inspect the blend door's wiring and connections for an open circuit. Technician B says to troubleshoot this circuit with a test light. Who is correct?

TECH A is correct. An open in the circuit would prevent the blend door's motor operation.

During a visual inspection an oily spot is found on a hose leading from the compressor. Technician A says there may be a refrigerant leak in the system. Technician B says today's R134a systems use mineral oil instead of the older R12 compatible PAG oil. Who is correct?

TECH A is correct. Finding an oily spot on an A/C hose is a quick and easy way to spot a refrigerant leak. Closer inspection and testing will be necessary.

Technician A says the clutch relay protects the control head from the clutch circuit's high current. Technician B says open clutch relay windings result in compressor clutch engagement at all times. Who is correct?

TECH A is correct. Technician A is correct. A relay is a device used to protect control devices like PCM's from the high current used to power devices like an A/C clutch or a radiator fan.

Technician A says while performing a retrofit from R-12 refrigerant to R134a refrigerant, the refrigerant must be recovered into a dedicated cylinder, they cannot be mixed. Technician B says R-12 refrigerant functions at higher pressures than R-134a refrigerant does. Who is correct?

TECH A is correct. The two refrigerants cannot be mixed. A separate, dedicated R-12 refrigerant container is used. Each refrigerant has its own color assignment. R-12's assignment is white and R-134a is sky blue "light blue".

A CCOT system has a high high side. Technician A says to suspect the thermostatic expansion valve. Technician B says this system contains an orifice tube. Who is correct?

TECH B is correct. A clogged orifice tube will result in high high side pressure. It can become clogged with contaminants, debris from a damaged compressor, or a broken desiccant bag releasing desiccant into the refrigerant.

Two technicians are discussing a CCOT air conditioning system. Technician A says the system's pressure cycling clutch switch contains a bulb placed on the inlet port of the evaporator core. Technician B says a pressure cycling switch is located on the low side of the system. Who is correct?

TECH B is correct. A typical pressure cycling switch is located on the accumulator or the low side of a system.

A (TXV) thermostatic expansion valve system blows cold air for five minutes and then goes warm. Technician A says this condition is caused by a low refrigerant charge. Technician B says this condition is caused by moisture in the system. Who is correct?

TECH B is correct. After a few minutes moisture freezes in the expansion valve restricting refrigerant from entering the evaporator core. A saturated receiver drier will result in this condition.

Technician A says evacuating an air conditioning system will remove air, debris, and moisture. Technician B says to evacuate the system any time it's been exposed to the atmosphere. Who is correct?

TECH B is correct. Always evacuate the system if it's been exposed to the atmosphere.

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?

TECH 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.

Technician A says an ambient temperature sensor senses cabin air temperature. Technician B says a faulty ambient temperature sensor can prevent compressor clutch engagement. Who is correct?

TECH B is correct. The automatic temperature control module uses several input sensors. The ambient or outside air temperature sensor is a variable resister. If the outside temperature is colder than the factory set value, or the sensor or it's circuit is faulty, the automatic temperature control will not engage the compressor clutch.

A blower motor operates only in high speed. Technician A says there could be a short in the motor's power feed. Technician B says it may have a faulty blower motor resistor. Who is correct?

TECH B is correct. The blower resister's lower speeds share the same power source and offer varying resistance, while the high speed selection is on it's own circuit and has no resistors.

Technician A says a fixed orifice tube varies the flow of refrigerant in relation to temperature. Technician B says a fixed orifice tube is located between the condenser and the evaporator. Who is correct?

TECH B is correct. The fixed orifice tube is located between the condenser and evaporator core.

A compressor clutch coil is being tested. There is 12 volts at the connector and the ground is good. The resistance of the coil is 0.00 Ohms. Technician A says the coil has an open in it's windings. Technician B says the clutch coil has a short and has failed the resistance test. Who is correct?

TECH B is correct. The test indicates that the circuit is providing within a volt of battery/charging voltage which is good, but indicates that there's a short in the coil. The clutch coil must be replaced.