The air conditioning uses a refrigerant and various components to cool down the inside of the vehicle. The main components are the compressor, condenser, dryer, expansion valve, evaporator and the blower fan. The compressor compresses the refrigerant making it change into liquid phase. The compressing of the gas causes the liquid's temperature to rise. Then as it goes through the condenser the liquid is cooled down by wind passing through the condenser and removing the heat. The liquid then goes through the dryer where any moisture is taken out. The liquid then goes to the expansion valve where the amount of liquid that flows into the evaporator is controlled. As the Liquid is released by the expansion valve and it goes into the evaporator. The pressure in the evaporator is lower than the pressure in system before the expansion valve. The lower pressure causes the refrigerant to change phase from a liquid to a gas. As the liquid changes to gas the temperature also drops. The temperature of the gas in the evaporator is less than the temperature of the refrigerant gas before it was compressed because heat has been removed from the refrigerant when it was in liquid form by air passing through the condenser. With the evaporator at a low temperature the vehicle can be cooled by the blower blowing air through the evaporator through the vents into the cab of the vehicle.
There are different types of air conditioning compressors, the two that we dis assembled were the piston type and the vane type compressors. The piston type works very similar to an internal combution engine and the vane type is similar to a oil pump or power steering fluid pump. The main reasons why a compressor will fail is that the bearings wear out (due to a lack of lubrication, general wear and tear or a fan belt that is over tightened creating more strain on bearings), the refrigerant leaks out, one of the switches are faulty in the electrical circuit or the compressor clutch is faulty .
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| Piston Type |
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| Vane Type |
When checking the air conditioning on the suzuki we found that the temperature at the vents were not cool enough. We check the compressor to see if the clutch engages when the air conditioning is switched on. we noticed that the compressor does not come on. We thought it may be that the refrigerant was low so we by passed the pressure switch to see if the compressor works. The compressor's clutch would still not engage, this could only mean that the circuit was broken before the pressure switch. We then went to check the fuse to find that it had been removed. Replaced the fuse and the air conditioning works.
Another vehicle had the same problem. The vehicle was a Mercedes Benz c200, the compressor clutch did not engage. We checked for faults using the Hannatech scanning tool. There was a few faults in the air conditioning system and one of them was that the refrigerant was low. We confirmed that the refrigerant was low by checking the current data of the air conditioning system using the diagnostics tool, which showed that the pressure in the system was zero bar. We then connected the manifold guage set to the car and that confirmed that the refrigerant was low.
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| Manifold guage |
Using the same Manifold guage set we created a vacuum in the system using the recovery unit and left it for fifteen minutes to check if the system had any leaks. It is important to check that the system has no leaks otherwise there would be no point recharging the system with refrigerant as it would just leak out. After fifteen minutes the guage was still in the same position indicating that there were no major leaks in the system. We then connected the manifold guage to the scale that was connected to the charging cylinder. If the system is charged on the low pressure side the charging cylinder should be facing upwards so that the system is charged with gas. If the system is charged on the high pressure side the cylinder should be upside down so that he system is charged with liquid. Once the system was charged we closed of the the tap going to the scale/charging cylinder but left the manifold guage connected to the air conditioning system so that we could see if the compressor was working correctly. We started the car, switched the aircon on , put the fan on high, switched the vents to blow out the top and set the temperature to cold. The compressor clutch engaged and the pressure on in the system increased to the correct pressure. The system was cycling correctly and the temperature inside the cabin was correct. We then checked the system again with the diagnostics tool, the current data displayed that the pressure in the system was now 15 bar.
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The R134a refrigerant has a die in it that can be seen using a infrared light.
It used to find leaks in the air con system |
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screen shot of the Hannatech diagnostics tool after the
refrigerant in the system was recharged notice that the
refrigerant pressure is at 15 Bar not 0 as before |
An air conditioning circuit in a car has many safety features/controls to protect the compressor from running without lubrication and ceasing when the refrigerant is low. It also stops ice building up on the air conditioning system by stoping the compressore when the evaporator temperature goes too low or if the preassure in the system is too high or too low. The safety features/controls switches the compressor on and off to keep the vehicle cool while keeping the system in a safe working order. The switching on and off of the compressor is called cycling.
