Air Conditioning
- Compressor, swept volume 160 cm3
- Condenser
- Drier (integrated)
- Pressure sensor
- Service valves
- Heat exchanger
- Thermal expansion valve (TXV)
- Evaporator
The air conditioning only operates in outside temperatures above 0 °C. In lower temperatures, the pressure in the system becomes too low and the compressor is not engaged. The reason for this is to prevent the moisture on the surface of the evaporator from freezing to ice and building up, which may impede function or damage the evaporator.
The air conditioning only operates when the engine is running. It operates regardless of engine speed and vehicle speed. The compressor is disengaged on kickdown in order to provide enhanced output for acceleration during overtaking, for example. The output of the air conditioning is regulated via the compressor's swept volume as well as via the climate unit's fan.
The blower fan must be operating before the climate control system can be engaged.
The evaporator (8) receives the liquid refrigerant. The drier (3) is integrated into the condenser. The compressor (1) is a pump that pressurizes the refrigerant. The heat transfer takes place in the condenser (2). The expansion valve (7) regulates the flow of refrigerant to the evaporator.
| 1. Compressor | 6. Evaporator |
| 2. Condenser | 7. Blower fan |
| 3. Engine cooling fan (the same cooling fan used by the engine cooling system) | 8. Thermal expansion valve, TXV, rear |
| 4. Receiver drier | 9. Evaporator, rear |
| 5. Expansion valve, TXV | 10. Blower fan, rear |
| A | High pressure, hot liquid | C | Low pressure, cold gas |
| B | Low pressure, cold liquid | D | High pressure, hot gas |
| Dark arrow | Hot air | ||
| Light arrow | Cold air | ||
| E | Front A/C | F | Rear A/C |
The cooling system is divided into:
- a low pressure side (B, C)
- a high pressure side (A, D).
The low pressure and high pressure sides are separated by the compressor (1) and the expansion valve (5). The evaporator (6) is located on the low pressure side and the condenser (2) is on the high pressure side.
The design of the air conditioning in a vehicle is based on the natural laws which mean that liquids are evaporated when exposed to temperature increase or pressure reduction and that heat is absorbed during this process. If the hot vapor is then cooled down again, the heat that was absorbed is released and the gas reverts to liquid form. This process can be repeated as many times as needed, so that "cold is produced" continuously. This is the same type of process used in a refrigerator, for example.
The compressor pumps up the pressure of the refrigerant and sends it to the condenser where it is cooled and condenses. The expansion valve reduces the pressure and the temperature of the refrigerant, which is heated by the incoming passenger compartment air. The passenger compartment air passes via the evaporator, which causes the refrigerant to boil (evaporate). The refrigerant then returns to the compressor.
The system with rear A/C climate unit uses a parallel system with its own expansion valve, evaporator and fan. The system is filled with well-adapted amounts of refrigerant and oil. The function of the oil is to lubricate and seal the compressor (piston and cylinder). The refrigerant has an additive of fluorescent leak detection agent that makes it possible to trace leaks using UV light.
In systems with rear A/C climate unit, there are two evaporators: one front (main evaporator) and one rear evaporator, as well as expansion valves for each evaporator.
To control this, there is a temperature sensor in the air flow after the evaporator. The temperature sensor detects the temperature of the air that has passed through the evaporator. When the temperature is too low, the compressor is switched off. This is to prevent ice forming on the evaporator.
Rear evaporator and expansion valve
| 1. Evaporator, rear | 2. Expansion valve (fixed orifice) |
| 3. A/C shut off valve | |
| 4. Filter for expansion valve | |
| 5. Refrigerant in liquid state, low pressure, to the rear evaporator | |
| 6. Refrigerant in gas state, low pressure, to the compressor |
Rear evaporator
The rear evaporator is connected in parallel to the system via A/C pipes that are connected close to the front expansion valve under the plenum cover. These A/C pipes are routed into the passenger compartment along the floor back to the rear climate unit.
Rear expansion valve with shut-off valve
The rear evaporator is equipped with an expansion valve with fixed restriction. The restriction is so small that particles in the A/C coolant system can attach to or clog the valve. The valve is equipped with a conical metal filter that traps particles that are sufficiently large.
The expansion valve is integrated in the nozzle to the electric shut-off valve that is used to connect and disconnect the rear A/C climate unit from the system. The shut-off valve is normally closed, and opens fully when powered by the climate control when rear A/C is necessary.
Cooling cycle
- Condenser
- Expansion valve
- Evaporator
- Compressor
In the cooling cycle, heat is transported from a colder area to a warmer one. The refrigerant is the medium that absorbs and releases heat from the area to be cooled and which then emits heat in another location.
Evaporated refrigerant is led into the compressor where its pressure and temperature increase. The hot, compressed refrigerant vapor now has a temperature and a pressure at which it can be condensed and led through a condenser. Here it is cooled by air that flows around the condenser coils and is condensed to a liquid. In this way, the circulating refrigerant releases heat from the system, and the heat is led away by the air.
The condensed, pressurized and normally hot refrigerant is then led through an expansion valve where the pressure is rapidly reduced. The pressure reduction means that part of the refrigerant is quickly evaporated, and the temperature decreases.
The cold refrigerant is then led through the evaporator. A fan blows the air to be cooled through the evaporator, which causes the refrigerant mixture to be evaporated - so further reducing the temperature. The hot air is cooled down and blown back into the compartment.
In order to complete the cooling cycle, the refrigerant is led back into the compressor.