System With Expansion Pipe
Expansion Pipe ("orifice")
Passive flow regulator (= fixed choke valve).
Consists of a thin metal pipe which is positioned in a plastic housing with a filter on both the intake and outlet sides. The filter collects any impurities in the system. Passive flow regulator (= fixed choke valve).
Governs the volume of refrigerant which is released from the evaporator.
The volume is affected by the dimensions of the pipe (diameter, length) and the pressure and temperature on both sides of the pipe.
The pipe is adjusted for its system and for the type of refrigerant that is used.
The pipe for the R12 has a greater diameter than the pipe for the R134a. This is because the R12 and oil mixture has a higher viscosity than the oil and R134a mixture.
Governs the system's capacity and functions as an anti-freeze
Consists of a switch which is affected by the pressure of the refrigerant downstream of the evaporator, in other words on the lower pressure side (the pressure switch (Pressostat) must be positioned as close to the evaporator outlet as possible.
If the pressure is too low (= too low temperature the pressure switch (Pressostat) interrupts a current circuit and the compressor is switched off. This is so that the water that condenses on the evaporator does not freeze to ice and obstruct the airflow through the evaporator. Heavy build up of ice can also cause damage to the evaporator.
When the pressure (= temperature) increases again, the pressure switch (Pressostat) closes the current circuit and the compressor is engaged.
The pressure switch (Pressostat) opens at approximately 1.6 bar and closes at approximately 3.2 bar.
Receiver drier
On systems with an expansion pipe, the pipe may in some cases allow through a little too much refrigerant. The result is that a little of the refrigerant will be released from the evaporator in liquid form. To prevent damage to the compressor, the receiver drier must be positioned on the low pressure side and be able to separate liquid from gas.
The receiver drier outlet is located so that only refrigerant in gas form can leave the receiver drier. Refrigerant in liquid form is collected in the bottom of the receiver drier.
The refrigerant in the bottom of the receiver drier contains a relatively high amount of oil. This mixture (refrigerant and oil) is led through a calibrated hole out into the outlet pipe and is transferred with the gas back to the compressor.
The hole plays a very important role in the return of oil to the compressor.
Control of the temperature in the passenger compartment
The air conditioning system has only two positions, off and on.
If it is too cold in the passenger compartment, the temperature can be controlled with the normal heat and blower fan controls.
Service socket
On systems with an expansion pipe, there is often only one nipple (on the low pressure side) to which the A/C station or pressure gauge can be connected.