Automobile Air Conditioning
This chapter deals with all the possible aspects of heating and air conditioning systems for automobiles. The chapter covers ;
• Air Conditioning Requirements
• Theoretical Analysis of Refrigeration Circuits
• Components of Refrigeration Systems
• Refrigerant and Refrigerant Oil
• Heater System
• Vacuum Circuits, Control Devices and Electrical Circuits
• Pressure and Temperature Controls
• Dust System
• Heater and Air Conditioning Service
33.1.
Air Conditioning Requirements
The automobile compartment is heated due to several factors such as,
(i) higher temperature of outside air,
(ii) solar radiation, and (Hi) engine heat.
The amount of heat absorbed is dependent upon,
(a) automobile insulation,
(b) position of sun and intensity of solar radiation,
(c) variation of light and shadow,
(d) vehicle colour,
(e) tinted glass,
(f) vehicle speed, and
(g) wind direction and velocity.
An automobile air conditioner must be capable of removing all the heat inputs in addition to reducing and maintaining the temperature of the compartment of the vehicle in the comfort zone. Besides temperature, humidity is also one of the comfort factors and in many cases it is an even more important factor. Therefore, removal of excess humidity is also one of the requirements of air conditioning.
Heat load on the air conditioner for customary units is expected to be as high as 4400 J/s,’ which is equivalent to 1.5 tons of air conditioning. About half of this heat is conducted through the body metal and glass and the remaining comes from air leaks and warm parts within the compartment. The air conditioner can transfer about one third of this heat at engine idle and hence full air conditioning is attained only at raised engine speeds.
The cars were first sold with an air conditioning system as a standard optional, in the early 1950′s. Most of the system uses a 1.5 kW refrigeration compressor located under the engine hood and belt driven from the crankshaft. Air conditioning systems were first applied to trolleys for fleet operation in 1938 and in 1942 many buses were also air conditioned. Capacities of air conditioning systems range from 3.5 to 4 tons for trolleys and 35 to 40 tons for buses. Mechanical compression units are being driven from the main engine or by a separate gasoline engine.
Fig. 33.1. Typical air distribution system.
