Tài liệu học tập cơ bản khái quát về động cơ và các bộ phận trên ô tô phiên bản tiếng anh. Tài liệu này nhằm giúp chúng ta tiếp cận được cấu tạo chức năng của các bộ phận của xe. Với tài liệu này giúp các bạn sinh viên ngành cơ khí ô tô tiếp cận được những kiến thức cơ bản về ô tô và đồng thời nâng cao kiến thức tiếng anh. Bộ tài liệu này được soạn thảo bởi trường đào tạo và huấn luyện nghề ở Canada.
Chapter 53 Air-Conditioning Diagnosis and Service Service Precautions • Wipe away any oil or dirt before disconnecting a connection • Keep tools clean and dry • Refrigerant oil containers must be clean and dry • Leave a system open for the shortest time possible • Evacuate a system any time it has been opened Refrigerant Safety Precautions • Work in a well-ventilated area • Refrigerant will cause frostbite if it contacts exposed skin or eyes • Wear protective gloves and clothing in addition to eye protection • Never use compressed air to leak test a R-134a system Refrigerant Safety Precautions • Never drop, strike, puncture, or burn a refrigerant container • Never expose A/C systems or refrigerants to high temperatures or open flame • Never overfill refrigerant containers • Never mix R-12 and R-134a, components, or equipment Special Precautions for Hybrid Vehicles • The A/C is usually powered by the highvoltage system • Follow all precautions and service procedures given by the manufacturer • Ensure the use of the correct refrigerant oil Initial System Checks • • • • • • Verify the complaint Check operation at full heat and full cold Pay attention to smells and noises Inspect the compressor drive belt Look for a film of oil leakage Check for condenser airflow restrictions Simple Checks • Vent outlet temperatures • Blower speeds • Feel for temperature differences of high and low side hoses • Expansion valve should be frost free • Check the sight glass if equipped Trouble Codes • May have selfdiagnostic capability • Automatic climate controls are very likely to have codes and data Diagnosis • Noise – – – – Clutch noises Hose noises Compressor noise Hissing and whistling • Odors – Moldy or musty smells – Cabin air filters Performance Testing • Connect a manifold gauge set • Use temperature/pressure charts as a guide • Monitor discharge temperatures with a thermometer Compressor Controls • Check various control switches for resistance or continuity: – – – – – – – Ambient temperature switch Thermostatic switch Pressure cycling switch Low-pressure cutoff switch Electronic cycling control switch High-pressure cutoff switch Evaporator temperature sensor Hoses and Fittings • Total hose replacement is the preferred method to correct a hose leak • Inspect fittings • Spring lock fittings require special tools • Lubricate new O-rings with refrigerant oil Receiver/Dryer and Accumulator • Should be changed when there has been a leak and/or component replacement • The desiccant rapidly draws moisture and can be contaminated in less than minutes • Keep new unit sealed until ready to install Evaporator • Some can be replaced from under the hood or under the dash • Many require dash removal to replace • Inspect the evaporator drain: – Inadequate or no draining will allow water to back up into the evaporator case – Can cause wet floorboards and mildew smells Evaporator Controls • Newer models use orifice tubes • Insert removal tool and remove tube • Coat new tube with clean refrigerant oil Condenser • Normally only needs replaced if leaking or damaged • Once removed, drain oil into a graduated container • Add the necessary amount of new oil to the new condenser • Coat O-rings with new oil Recharging the System • Evacuate the system to remove all trapped air and moisture • The vacuum pump should remain connected for at least 30 minutes after 26 to 29 inches of mercury is reached Charging • Refrigerant is added through the service ports • Charge only through the low side when the system is operating • Some vehicles charge through the high side with the system off Charging Cylinder • To accurately measure charging by cylinder weight, it is necessary to compensate for variations caused by temperature • A calibrated chart is used based on tank pressure Climate Control Systems • Most systems have self-diagnostics • Inspect blower motor operation • Check operation of controls, doors and ducts • Solar sensor operation may be checked through scan data ... between 1500 and 2000 rpm Close all vehicle windows and doors Set A/C to maximum cooling Check gauge pressures and outlet temperature • Refer to the manufacturers temperature and pressure charts... General Service • All refrigerant must be recovered • Component replacement may require the addition of refrigerant oil to system • Use the specific type and quantity oil required • Too much oil reduces... manufacturer’s procedures • Recover until gauges show vacuum Recycling • All recycled refrigerant must be safely stored in DOT CFR Title 49 or ULapproved containers • Before reuse, the refrigerant