【正文】 production and service procedures must emphasize the need for system dehydration and limited exposure of the lubricants to atmospheric moisture. Older Vehicles. Vehicles originally equipped with R12 do not require retrofit to another refrigerant as long as an affordable supply of new or reclaimed R12 exists. When circumstances require it, most air conditioners can be modified to use R134a and POE. When PAG oil is used in a retrofit, the remaining mineral oil should be removed to levels established by the original equipment manufacturer to prevent residual chlorides from breaking down the PAG. R22 is not suitable for topping off or retrofit in R12 systems, as it will produce unacceptable discharge pressures (up to MPa at idle) and temperatures. R12 idle discharge pressures can reach MPa。C for other floor areas, 63176。C. Physical Parameters Parameters include engine rock, proximity to adverse environments, and Rock. Relative to the rest of the car, the engine moves both fore and aft because of inertia and in rotation because of torque. Fore and aft movement may be as much as 6 mm。 (2) drive ratio, from :1 to :1。C are occasionally encountered. Because the system is an integral part of the vehicle detail, the effects of vehicle heat and local heating must be considered. Ambient Contaminants. Airborne bacteria, pollutants, and corrosion agents must also be considered when selecting materials for seals and heat exchangers. Electronic air cleaners and filters have been installed in premium automobiles. Vehicle Performance . Proper engine coolant temperature, freedom from gasoline vapor lock, adequate electrical charging system, acceptable vehicle ride, minimum surge due to pressor clutch cycling, and good handling must be maintained. Flexibility . Engine coolant pressure at the heater core inlet ranges up to 280 kPa (gage) in cars and 380 kPa on trucks. The engine coolant thermostat remains closed until coolant temperature reaches 71 to 96176。C. Airconditioning systems with reheat are evaluated from 4 to 43176。 (2) it permits promise standards where space considerations dictate (ventilation reduction on airconditioned cars)。 (3) it generally reduces the number and plexity of driver controls。C。C. Coolant flow is a function of pressure differential and system restriction but ranges from 40 mL/s at idle to 630 mL/s at 100 km/h (lower for water valve regulated systems because of the added restriction). Presentday antifreeze coolant solutions have specific heats from to kJ/(kg (3) condenser air, from 10 to 50176。 rotational movements at the pressor may be as much as 20 mm due to acceleration and 13 mm due to deceleration. Proximity to Adverse Environments. 山東建筑大學(xué)畢業(yè)設(shè)計(jì)外文文獻(xiàn)及譯文 4 Wiring, refrigerant lines, hoses, vacuum lines, and so forth, must be protected from exhaust manifold heat and sharp edges of sheet metal. Normal service items such as oil filler caps, power steering filler caps, and transmission dipsticks must be accessible. Airconditioning ponents should not have to be removed for servicing other ponents. Durability . Hours of operation are short pared to mercial systems (260 000 km 247。C for dash and toe board, and 43176。 in addition, it may be inpatible with the elastomeric seals and hose materials. Several blends of two or more refrigerants are being sold as“dropin” replacements for R12. They should not be used without a thorough investigation of their effect on performance and reliability under all operating conditions. Other concerns include (1) flammability, (2) fractionation, (3) evaporator temperature glide, (4) increased probability of adding the wrong refrigerant or oil in future service, and (5) pounded plexity of refrigerant reclaim. Condensers Condensers must be properly sized. High discharge pressures reduce the pressor capacity and increase power requirements. When the condenser is in series with the radiator, the air restriction must be patible with the engine cooling fan and engine cooling requirements. Generally, the most critical condition occurs at engine idle under high load condit