How the Cooling Unit Works
1. Evaporator
When the refrigerant comes from the expansion valve in to the evaporator, it expands. The pressure in the evaporator is much lower due to the suction effect of the compressor. As refrigerant expands, it becomes gaseous (boils). However, in order for evaporation to take place, heat must be supplied. This heat is taken from the air around the evaporator. The cold air is then blown into the cabin by the fan. Refrigerant is then directed on in gaseous form to the compressor.
2. Anti-freeze thermostat
The anti-freeze thermostat prevents freezing and the build up of ice on the evaporator. A capillary tube is inserted between the evaporator cooling fins and senses temperature. When temperature drops below about +1.5° C (35° F), power to the compressor clutch is interrupted. When evaporator temperature then increases to about +4.5° C (40° F), the thermostat closes and the compressor is switched on again.
3. Compressor
Refrigerant arrives at the compressor under low pressure and in gaseous form. In the compressor, the refrigerant is compressed and its pressure and temperature increase. The warm gaseous refrigerant is then forced on into the condenser.
6. Expansion valve
The refrigerant which comes into the expansion valve is liquid, at high pressure and high temperature. The function of the expansion valve is to control the quantity of refrigerant which is sprayed into the evaporator. The valve does not let in more refrigerant than that quantity which can be evaporated at any particular time.
In order for the expansion valve to be able to let through the exact quantity of refrigerant, there is temperature sensor and a capillary tube.
5. Desiccant container
The function of this is both to store and desiccate the refrigerant.
The refrigerant comes in to the desiccant container in liquid form under high pressure and at high temperature.
It passes through a filter where it is desiccated and where any particles are separated. The refrigerant is then led on in liquid form to the expansion valve.
There is a pressure switch on the desiccant container which disconnects the compressor if pressure becomes too low in the system.
4. Condenser
The hot refrigerant at high pressure is pumped by the compressor in to the condenser's cooling coil. The cooling coil has cooling fins, which are cooled by air from the car's radiator fan and the natural air circulation through the car. As heat always moves from a warmer to a cooler object, the hot refrigerant will transfer a part of its heat to the colder air. When the hot gaseous refrigerant looses some of its heat, it starts to condense and return to liquid.
On the gas side of the condenser is a mechanical safety valve which releases refrigerant if system pressure becomes too high.
Diagram, A/C