Air Conditioning
Air conditioning
System overview
1. Linear pressure sensor
2. Service valve high pressure side (filling)
3. Service valve low pressure side
4. Evaporator
5. Temperature sensor
6. TEV
7. Condenser
8. Thermo switch
9. Compressor
10. Receiver drier
Evaporator
The heat from the incoming air is transferred to the refrigerant which converts to a gas. The following modifications are made by comparison with the S70/V70:
- Yellow chromating of the surface to prevent corrosion. A polyurethane coat to avoid bad odors. The polyurethane coating reduces the water surface tension which means that it runs off.
- The drainage pipe with the collection plate is installed downstream of the evaporator and exits through the firewall.
Compressor
The following changes have been introduced by comparison with the compressor on the S70/V70:
- The same basic concept as the compressor but a larger cylinder displacement, 167 cm3⇒higher capacity.
- Maximum acceleration compressor disengagement for at least 10 seconds but a maximum of 20 seconds.
The starting process for the air conditioning compressor
If the engine coolant temperature (ECT) is warmer than -7°C, the air conditioning relay is controlled by the engine control module (ECM). This is so that the compressor engages every time the car is started. The compressor is engaged during the start process in exactly the same way as when the air conditioning (A/C) is selected.
- Engagement occurs during the starting process regardless or not of whether the air conditioning (A/C) is selected or not.
- Engagement continues for 100 engine revolutions. The compressor is then disengaged.
- If the air conditioning (A/C) is selected, the compressor continues to be driven.
The starter motor has a lower engine speed (RPM) than the car engine. As a result, the pressure in the compressor is not as high. The risk of the safety valve being activated is eliminated and any liquefied refrigerant is driven out of the compressor.
Temperature sensor
The anti-freeze protection for the system consists of a temperature sensor. This measures the temperature of the airflow which has just passed the evaporator. The sensor has a capacity controlling function. This switches the compressor on / off to prevent condensation freezing. The following modifications have been introduced.
- The sensor is located downstream of the evaporator. This makes it easier to install / replace the component.
- The sensor transmits a signal to the climate control system. The climate control system transmits the signal on to the engine control module (ECM). The ECM regulates the switching on / off for the air conditioning relay. The A/C relay switches off the compressor (at 4.0 - 6.9°C) and on (at 4.8 - 7.5°C). The control module can delay the engagement or temporarily disconnect the compressor under full acceleration.
Condenser
The refrigerant is cooled and condensed in the condenser. The refrigerant fluid continues to the drier unit in the refrigerant reservoir.
Receiver drier
To facilitate any leak tracing, a fluorescent agent is added to the receiver drier at the factory. This mixes with the system oil during operation.
Service valves
The air conditioning must be filled with 1000 grams of refrigerant. Refrigerant may only be topped up on the high pressure side of the system. This is to avoid the risk of liquid refrigerant entering the compressor. The valves are different sizes. This is to avoid incorrect connection. The service valves can be used for:
- Checking through the manometer connections.
- Draining the refrigerant from both valves.
- Evacuating / vacuum cleaning through both valves.
- Filling with refrigerant on the high pressure side.
Note! Refrigerant may only be topped up on the high pressure side of the system. This is to avoid the risk of refrigerant entering the compressor.
TEV
The valve is a pressure and temperature dependent block type flow regulator. If there is a low cooling requirement, the amount of coolant is reduced by closing the valve. If the amount of cooling increases, the valve will open slightly. This allows more fluid into the evaporator.
The thermostatic expansion valve (TEV) has a larger register than a system with a fixed choke. This is because the refrigerant volume can be more accurately controlled according to the cooling requirements.
Linear pressure sensor
The linear pressure sensor is installed directly on the receiver drier. The pressure sensor has an integrated measurement amplifier. This provides an output voltage which is linear to the pressure (0-35 bar). The signal is used to control the following functions:
- The engine cooling fan (FC).
- Compressor disengagement at high pressure (greater than 30 bar).
- Compressor disengagement if the system is completely empty (less than 1.76 bar).
The pressure sensor cannot be replaced without draining the system first.
Thermo switch
The thermo switch switches off the compressor when the material temperature exceeds 135°C. It switches on again when the temperature is below 120°C. It switches off to prevent the compressor seizing.
Normally this material temperature occurs only in the following combination of circumstances:
- Low refrigerant level.
- The vehicle speed is greater than 70 km/h.
- The outside temperature is greater than 30-35°C.