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How does car air conditioning work?
An air conditioner is a quite specific piece of equipment, which operates in extremely harsh conditions. Its work requires efficient cooling of air, which is performed by a compressor, a condenser, a dehumidifier, an expansion valve and an evaporator, as well as a special gaseous cooling agent flowing through the whole system. In turn, the correct operation of the entire system is monitored by an air conditioning pressure sensor, whose principle of operation we will describe later in this article.
The aforementioned coolant plays a key role in the cooling process. Its task is to transfer thermal energy and thus reduce the air temperature. This is done by compressing the medium with a compressor, which in turn causes it to heat up considerably. The refrigerant is then transferred to a condenser which also acts as a heat exchanger.
Later on, the cooled refrigerant passes through a dehumidifier and finally reaches an expansion valve where, as a result of a sudden drop in pressure, the refrigerant cools down considerably. The cooled refrigerant then passes through an evaporator, or in other words a heat sink, which lowers the temperature of the air passing through it before it enters the vehicle cabin.
So it’s not hard to conclude that the A/C system works mainly by changing the coolant pressure. But the whole system is extremely sensitive to overcharging – if the compressor is constantly running at maximum speed, the rising pressure can burst the A/C pipes, leading to a dangerous leak. Therefore, a special A/C pressure sensor is used to prevent this situation.
What is the role of the air conditioning pressure sensor?
The primary task for which the A/C pressure sensor is responsible is to ensure that the refrigerant works at the optimum operating pressure. This is extremely important, as the cooler system is subjected to very high loads of up to 30 bar.
The vehicle’s A/C compressor, which operates at maximum efficiency, is able to compress the refrigerant at a much higher pressure. An A/C pressure sensor (also known as a pressure switch) is therefore installed in the system and is directly responsible for controlling the compressor. As soon as it detects that the permissible threshold is exceeded, it immediately disconnects the compressor.
The A/C pressure sensor is also a safeguard against possible leakage and refrigerant leakage – if the pressure in the system is too low, it will prevent the compressor from starting up, thus protecting it against seizure.
What types of A/C pressure sensors are there?
The A/C pressure sensor comes in two variants – analogue and digital, so the diagnosis procedure must be selected accordingly to the type of pressure switch used in the car.
An analogue A/C pressure sensor usually consists of a membrane, which closes or opens an electrical circuit depending on the refrigerant pressure, thus providing a signal to switch the compressor and fans on or off.
The digital A/C pressure sensor, on the other hand, is usually a piezoelectric sensor, which depending on the measured value of the refrigerant pressure starts to emit a precisely defined voltage. This data is then transmitted to the vehicle computer, which controls the entire air-conditioning system on the basis of programmed values.
Can you check the function of the A/C pressure sensor yourself?
Correct diagnosis of an A/C pressure sensor is quite a difficult task and usually requires the sensor to be removed from the system. It is also necessary to know the diagram of the air conditioning system that is used in the car.
nTherefore, in most cases, it is a much better idea to take the vehicle to a specialised mechanic, who will not only check whether the A/C pressure sensor is functioning properly, but also check the system for leaks and top up the refrigerant if necessary.
