Bus-air-conditioning system is composed of a light-weight engine and a compressor coupled together, and is mounted under the bus chassis. It has its own starting system, and once the sub-engine is running, the compressor runs together with it.
A cooling unit assembly house the evaporator coils. It is an aluminum finned aluminum tubing serpentine in shape where a blower blows the passenger compartment air through the finned coils into the individually arranged ducting going to the individual passenger seat roofing. Air nozzles are provided for aiding air direction inside the bus.
The condenser unit is made of copper tubing also serpentine in shape with aluminum fins to aide the heat dissipation better. A strong fan blows the air through the condenser tubing, thereby releasing the heat collected by the refrigerant into the atmosphere.
When the compressor of the bus-air-conditioning is running, it compresses the refrigerant coming from the evaporator into high-pressure and high temperature refrigerant gas. Together with the heat absorbed by the evaporator, the hot refrigerant travels into the condenser unit.
Upon reaching the condenser, the accumulated heat in the gas refrigerant is released into the atmosphere through the condenser fan. Once the heat is reduced the gas refrigerant turns into liquid refrigerant. The liquefied refrigerant now enters the receiver tank, where the high pressure refrigerant is stored.
It then passes through a drier/strainer device, small foreign materials like dirt, iron particles, and moisture in the refrigerant is filtered and strained. The dryer/strainer contains filter, desiccant, and stop-valves for maintenance removal of the device.
The filtered refrigerant now enters the sight glass, a device where you can see the liquid refrigerant travelling into the thermostatic expansion valve. The refrigerant through the sight glass should be like water, and not like small bubbles, because if it is so, it means the refrigerant is under charged.
The thermostatic expansion valve controls the flow of the liquid refrigerant into the evaporator. A sensing bulb is attached to the tube prior to the outlet of the evaporator. When the calibrated temperature difference between the inlet and outlet of the evaporator is breached, the valve open and let refrigerant to enter the evaporator, maintaining a constant volume of liquid refrigerant in the coils.
When the heat inside the passenger compartment is absorbed by the liquid refrigerant of the evaporator, the refrigerant boils and turns into gas. The temperature and the pressure drops as it enters the compressor, where it is being compressed and the refrigeration cycle repeats.
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