Questions and Answers
Who is correct regarding the electromagnetic clutch? Technician A says that the clutch will slip if the air gap is too close. Technician B says that the clutch will slip if the belt is close.
Who is correct regarding the seal seat installation? Technician A says that it is virtually impossible to insert the seal seat backward when using the appropriate tool. Technician B says that it is almost impossible to remove a seal seat that has been installed backward.
Most air-conditioning systems that have R-134a as the refrigerant also use _______________ as a lubricant.
Polyalkaline glycol (PAG)
Electric motor-driven air-conditioning compressors used on hybrid vehicles are based on what compressor design?
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All of the following statements about variable displacement compressors are true, except:
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Who is correct regarding the signs of oil spray on the compressor clutch hub? Technician A says that a leaking compressor shaft seal could be the cause. Technician B says that a faulty compressor clutch bearing could be the cause.
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Who is correct regarding the methods used to drive a compressor? Technician A says that automotive air-conditioner compressors have an electromagnetic clutch. Technician B says that a serpentine belt system is often used to drive a compressor clutch.
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A vehicle returns to the shop for a repeat failure of the compressor system due to compressor clutch slippage and overheating. What is the most likely cause?
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If the compressor oil has been drained and it shows signs of metallic particles, all of the following should be done, except:
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To measure and adjust compressor clutch air gap, a _______________ feeler gauge should be used.
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An air-conditioning compressor clutch failed due to overheating. What is the most likely cause of the failure?
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The angle of the swash plate in a variable displacement compressor is controlled by:
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A slipping compressor clutch may be due to all of the following, except:
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The following are automotive air-conditioning system compressor types, except:
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Who is correct about block or ladder diagrams for troubleshooting HVAC? Technician A says they aid in troubleshooting air-conditioning duct system faults. Technician B says the use of test lights is not recommended for under dash service.
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Who is correct regarding maintaining in-vehicle pressure? Technician A says that up to 20 percent of fresh air provides a means to maintain a positive in-vehicle pressure when the windows are closed. Technician B says this positive pressure is necessary to provide a proper balance of air pressure within the air delivery system.
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Who is correct about the vacuum reserve tank? Technician A says a vacuum reserve tank helps maintain a vacuum in the system at all times only when the engine is running. Technician B says that the check valve prevents vacuum loss when the engine is stopped.
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During normal comfort control operation with the windows closed, harmful gases are not allowed to enter the vehicle because:
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Who is correct about dealing with musty odors in HVAC systems? Technician A says when a musty odor develops, the odor-causing mold and mildew must be eradicated. Technician B says that a liquid antimicrobial deodorizer and disinfectant is used to eliminate odors in duct systems.
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A customer complains of the passenger compartment temperature always being too hot, cold, or not changing as the temperature range is changed on the control panel. On an electronic mode door actuator system, all of the following could cause this problem, except:
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A vehicle is brought into the shop with a complaint of weak airflow from all the dash vents. What is the most likely cause?
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Study Notes
Cooling System Issues
- Low coolant levels in a radiator can be caused by a faulty radiator cap or a cracked hose to the recovery tank; both are valid reasons.
- Performance issues may result from a partially blocked heater core leading to cool air from the heater.
Environmental Regulations
- The Clean Air Act led to the Montreal Protocol and provided the EPA with authority to control refrigerants for environmental protection.
Heat Transfer Concepts
- Convection transfers heat through surrounding air.
- Latent heat, described as hidden heat, is essential for a change of state and cannot be felt or measured with a thermometer.
Air Conditioning System Components
- A metering device converts high-pressure liquid into low-pressure liquid.
- The compressor acts as the boundary separating the low-side from the high-side in a refrigeration system.
- The receiver dryer is located at the condenser's outlet, storing some liquid refrigerant.
System Performance and Inspection
- Poor heating in the passenger compartment can occur from various issues, but a thermostat stuck closed is not a common cause.
- If a vehicle shows high pressure in the accumulator at improper temperatures, it indicates potential contamination.
Refrigerant Behavior and Analysis
- The compressor changes low-pressure vapor into high-pressure vapor and can lead to gauge discrepancies if defective.
- The presence of frost on the expansion valve indicates possible restrictions or valve issues.
Charging and Maintenance
- Proper charging of the A/C system requires that refrigerant be weighed to avoid overcharging, which reduces cooling efficiency.
- O-rings should be lubricated with clean refrigerant oil before installation.
Diagnostic Techniques
- High lead pressure during compressor engagement, even at both service ports, may suggest a restricted discharge hose.
- Electronic leak detectors need regular calibration and maintenance for accuracy.
Compressor Types and Functionality
- Scroll compressors facilitate low pressure conditions while boosting temperature and pressure.
- Variable displacement compressors do not use a cycling clutch, contrary to some beliefs.
Technical Procedures and Safety
- Safety measures are crucial, such as disconnecting power sources when servicing electric components.
- The evacuation process is vital for removing moisture and air from refrigerant systems.
Problems with A/C Systems
- A stuck open expansion valve or restricted inlet could be reasons for inadequate cooling from an evaporator.
- Leaking oil around the compressor may indicate issues with the compressor shaft seal or bearing.
General Maintenance Practices
- A proper understanding of compressor types (like H-block and swash plate designs) aids in diagnosing issues.
- Careful observation, such as checking for air gaps in clutches, is essential for optimal compressor function.
Terminology
- Superheat refers to heat added to vapor, while sensible heat can be measured with a thermometer.
- PAG is the common lubricant used with R-134a systems and requires precise attention during maintenance.### High Resistance in Electrical Circuit
- High resistance in the compressor clutch electrical circuit can lead to overheating, causing clutch failure.
Compressor Oil and Metallic Particles
- If metallic particles are found after draining the compressor oil, a heavier refrigeration oil must be added after flushing the system.
Measuring Air Gap
- A nonmetallic feeler gauge is required to accurately measure and adjust the compressor clutch air gap.
Causes of Clutch Overheating
- Overheating of the air-conditioning compressor clutch is most commonly due to high resistance in the compressor.
Swash Plate Control
- The angle of the swash plate in variable displacement compressors is controlled by the suction pressure differential within the crankcase.
Slipping Compressor Clutch
- A slipping compressor clutch can result from multiple factors except for a low refrigerant charge.
Types of Compressors
- Automotive air-conditioning systems do not typically include centrifugal compressors as a common type.
Troubleshooting Techniques
- Block or ladder diagrams assist in troubleshooting air-conditioning duct systems; using test lights under dash service is not advised.
In-Vehicle Air Pressure
- Fresh air intake, up to 20%, maintains positive in-vehicle pressure when windows are closed, aiding in air delivery system balance.
Vacuum Reserve Tank
- A vacuum reserve tank keeps a vacuum in the system only when the engine runs, while a check valve prevents vacuum loss when the engine is off.
Harmful Gas Prevention
- A slight positive pressure within the vehicle prevents harmful gases from entering during normal comfort control operation with windows closed.
Odor Management
- Addressing musty odors involves eradicating mold and mildew; liquid antimicrobial deodorizers and disinfectants effectively eliminate duct system odors.
Temperature Regulation Issues
- Complaints of inconsistent passenger compartment temperatures may arise from factors other than a faulty actuator in electronic mode door actuator systems.
Weak Airflow Causes
- Weak airflow from dash vents is most likely due to a dirty cabin air filter, impeding proper ventilation.
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Description
This quiz covers fundamental concepts related to heating and cooling systems, including cooling system issues, heat transfer methods, and air conditioning components. Test your knowledge on environmental regulations and the components that keep HVAC systems operating efficiently.
