In a fixed orifice tube system, the components necessary for system operation are:
The condenser, the evaporator, the compressor, the orifice tube, the accumulator, connecting pipes and hoses, a thermostat, blower fans and pressure switches.
The orifice tube is located between the condenser and the evaporator and provides the restriction to flow necessary for system operation.
When the air-conditioning system is switched on, an electro-magnetic clutch is energized on the compressor drive plate and the compressor is driven by the engine crankshaft.
Vaporized refrigerant is drawn from the low pressure side of the system by the compressor.
It is discharged from the compressor as a high-pressure, high-temperature vapor and flows to the condenser where it is cooled by the air flowing across the condenser coils and fins.
The reduction in temperature causes the refrigerant vapor to condense and turn into a liquid which flows to the filter and then to the orifice tube.
The liquid refrigerant loses pressure by flowing through the fine tube and is then forced to expand suddenly by passing through the nozzle and entering the larger volume of the evaporator.
The drop in pressure causes the low-pressure low-temperature liquid to boil and this liquid mist evaporates rapidly in the evaporator coils, absorbing heat from the air passing across the external fins.
The cooled air is directed to the interior of the vehicle by blower fans. The refrigerant in the evaporator flows on to the accumulator.
The accumulator acts as a storage volume for the refrigerant and also separates liquid from vapor.
Refrigerant vapor enters at the top of the accumulator. Any liquid refrigerant falls to the bottom.
The accumulator is made from aluminum and has a large surface area. This assists the final evaporation of any liquid refrigerant leaving the evaporator.
Refrigerant vapor is drawn off from the top of the accumulator through the outlet tube by the compressor.
At the bottom of the outlet tube is a small hole which allows a small amount of any lubricating oil that settles at the bottom of the accumulator to be drawn to the compressor.
The accumulator also contains filters and desiccants which remove impurities and moisture from the refrigerant as it passes through.
