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Air conditioning

 CARSTARS Garage car A/C system repairs in Dubai Al Quoz

A/C repairing specialists in Dubai

Car A/C repairing and a/c system service

The air heating system in the passenger compartment is not capable of providing the required temperature regime. At ambient temperatures exceeding 23°C, it must be cooled to create comfortable conditions for the driver and passengers. Air conditioning systems are used to solve this problem. The air conditioning system scheme is shown in the picture:

Picture: Air conditioning system in the car:

1 – Compressor; 2 – electrical clutch; 3 – capacitor; 4 – auxiliary fan; 5.7 – pressure sensor; 6 – receiver-dryer; 8 – temperature switch; 9 – thermal sensor; 10 – condensate tray; 11 – evaporator; 12 – evaporator fan; 13 – fan switch; 14 – pressure reducing valve

Car A/C repairs Dubai

Refrigerant A/C Gas replacement in Dubai

The system is filled with refrigerant, which, depending on temperature and pressure, can change from gaseous to liquid and vice versa. The refrigerant is the gas used to fill the system. Until recently, R12 freon was the refrigerant for car air conditioners. After the publication of the theory of the destruction of the ozone layer of the earth’s atmosphere by refrigerant fluorocarbons contained in the refrigerant R12, its use was reduced.

Modern air conditioning systems use R134a freon (tetrafluoroethane), which is considered “environmentally friendly”. This refrigerant belongs to the class of hydrofluorocarbons (HFC), does not contain chlorine and is not very harmful, but its efficiency is 10-15% lower than   R12, and it is more fluid. However, car air conditioners using R134a require a higher operating pressure to operate effectively. The use of the refrigerant R134a has led to the complication of air conditioning systems. It should be noted that the new and old refrigerants are incompatible since the compressor oils charged with them are incompatible.


Receiver replacement A/C repairing Dubai

At a certain temperature and a certain pressure, the cooled refrigerant condenses and turns into a liquid state. From the bottom, the refrigerant leaves the condenser and in a liquid state enters the receiver-drier, which consists of a receiver and a drier, installed on the condenser outlet pipe before the evaporator. The receiver-drier does not only provide storage of the refrigerant, but filters it and removes moisture (sometimes the filter is installed separately from the receiver). Moisture is removed by using a special adsorbent that has a limited service life.

Receiver 5 serves to smooth out fluctuations in the refrigerant flow.

Pic: Receiver-drier:

1 – Supply of refrigerant from the condenser; 2 – supply of refrigerant to the pressure reducing valve; 3 – drier; 4 – mesh filter; 5 – receiver

Drier 3 removes moisture that has entered the refrigerant circuit during installation or from the environment, as well as deposited wear products of compressor parts, dirt that got into the circuit during installation and other foreign impurities. The receiver-drier can be equipped with a sight glass to monitor the amount of refrigerant. In case of failure, the receiver-dryer is not repaired and must be replaced.

Pressure reducing valve replacement Dubai

After the dryer, the refrigerant flows to the pressure-reducing valve. The pressure-reducing valve in front of the evaporator lowers the pressure of the liquid refrigerant, which causes the evaporator to cool. The pressure-reducing valve is located at the boundary between the low and high-pressure sides of the refrigerant circuit. The valve regulates the flow of refrigerant to the evaporator, depending on the temperature of the refrigerant vapor at the outlet of the evaporator, therefore, the evaporator evaporates as much refrigerant as is necessary to maintain uniform “cold” in the evaporator.

If the temperature of the refrigerant leaving the evaporator rises, the refrigerant expands in thermostat 4, which is installed on the pressure reducing valve. In this case, the diaphragm 3 bends and the flow of refrigerant through the ball valve 2 to the evaporator increases.

Picture: Pressure reducing valve:

1 – Adjusting spring; 2 – ball valve; 3 – membrane; 4 – thermostat with sensor tube and refrigerant

If the temperature of the refrigerant leaving the evaporator decreases, then the amount of refrigerant in the thermostat decreases, and membrane 3 returns to the upper position. Refrigerant flow through the ball valve to the evaporator is reduced.

The thermostatic expansion valve operates under three forces:

  • The 1st pressure in the sensor tube depends on the temperature of the hot refrigerant. This pressure acts as releasing force (PFu) on the diaphragm.
  • 2nd evaporator pressure (PSa) acts on the diaphragm in the opposite direction
  • 3rd control spring pressure (PFe) acts in the same direction as the evaporator pressure

The pressure relief valve sprays the chilled liquid into the evaporator.

Car A/C Evaporator repairing in Dubai

The evaporator speeds up the evaporation process. For this, it has a large surface area and acts as a heat exchanger between the refrigerant and the ambient air. The refrigerant that has passed through the pressure reducing valve, becoming volatile with low pressure, when passing in a foggy state through the aluminum evaporator pipeline, under the action of the airflow from the fan, evaporates into a gas at a temperature of -2°C and a pressure of 2.0 kg/cm2. In this case, the fins of the evaporator pipe become cold from the heat of vaporization, and the air inside the car becomes cool. In addition, the moisture contained in the air turns into the water from cooling and, together with the dust, flows through the drainpipe into the condensate pan and then onto the ground.

Car A/C Compressor replacement in Dubai

The gaseous refrigerant is piped to the compressor, which is driven by the motor shaft. The compressor compresses the gas to high pressure. The compressor is powered by a clutch that is driven by the crankshaft pulley through the drive belt. If no voltage is applied to the clutch electromagnet, then only the compressor clutch pulley itself rotates and the compressor shaft does not rotate. When voltage is applied to the magnetic clutch, the disc and sleeve of the clutch move back and connect to the pulley. The pulley and disc under the action of forces become one and rotate the compressor shaft.

Climate control compressors are of various types:

  • piston chargers

  • spiral chargers

  • vane chargers

  • swashplate axial piston blowers

  • driven by an electric motor

Compressors with variable displacement axial piston types are the most widespread for air conditioning systems.

Picture: Scheme of a variable displacement axial piston compressor with a rotating swashplate:

1 – Runner; 2 – electromagnet; 3 – swashplate; 4 – piston; 5 – pump cylinder block cover; 6 – valves

A swashplate is connected to the drive shaft of the compressor, which during its rotation moves several (5…7) pistons. The body with cylinders is closed with a cover with a valve system. The compressor capacity is determined by the set cooling temperature. With these compressors, the inclination of the washer can change, which leads to a change in the piston stroke and, therefore, in the capacity. Compressors of these types have less impact on the engine operation when the clutch is engaged, which is very important for low-power engines. In addition, they provide greater stability at the set temperature.

The compressor, depending on the frequency of its rotating shaft, converts the gaseous state of the low-pressure refrigerant coming from the evaporator into a gas of high temperature and high pressure (80°C, 15 kg/cm2). The gaseous state of the refrigerant is necessary for the compressor because the liquid refrigerant cannot be compressed and this would destroy the compressor. The compressor seals the refrigerant and pumps it as hot gas into the condenser (high-pressure side of the refrigerant circuit).

Therefore, the compressor is separation place of the low and high-pressure sides of the refrigerant circuit.

In conclusion

The compressor is lubricated with a special compressor oil that circulates throughout the system along with the refrigerant. Mineral oils (with R134a – polyalkylene glycol (PAG)) are used in systems working with R12 freon. When these oils are mixed, a cloudy thick mass is formed, leading to the failure of the air conditioning system, and especially the compressor. When adding refrigerant and oil to the air conditioner, only those components are used that are designed for this system. As a rule, there are stickers in the engine compartment of a car. They are indicate the type of refrigerant, its amount and the corresponding type and amount of oil (stickers for R134а are green, for R12 – yellow).

Car A/C Condenser repair in Dubai

From the compressor, a hot gaseous refrigerant with a temperature of about 50…70°C is supplied to a condenser, which serves to convert the gaseous high-temperature refrigerant coming from the compressor into a liquid state by releasing heat into the atmosphere. The condenser consists of curved tubes that are connected by baffles and have a large cooling surface, which achieves a high heat transfer. The condenser tubes and louvers absorb the heat from the refrigerant.

The amount of heat generated by the refrigerant in the condenser is determined by the amount of heat absorbed by the evaporator from the environment and the compressor operation required to compress the gas. For a condenser, the result of heat dissipation directly affects the cooling effect of the refrigeration unit, therefore, it is usually installed on the front of the car and forcibly cooled by the air from the engine cooling fan or by an additional fan, and airflow generated when the car is moving. Cold outside air flows through the condenser, taking in heat so that the refrigerant is cooled.

Car A/C Pressure Sensors replacement Dubai

The air conditioning system is equipped with pressure sensors 5 and 7, which do not allow the system to operate when the refrigerant pressure in the system is below a certain value. To control the temperature regime of the system, temperature sensors 8 and 13 are provided.

In hot local climates, no car is complete without air conditioning. Some cars are equipped with a double circuit for so the rear passengers, which complicates the system but allows the rear passengers to separately control the temperature independently of the front ones. The most common problem is compressor failure or freon leakage. Both through the valves and through the evaporator, the replacement of which sometimes results in a pretty penny for the car owner. In our garage, we carry out any work with the air conditioning and heating system with a guarantee of diagnostics and quality work.


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Carstars Garage Dubai

Carstars garage in Dubai was founded in 2009 by expat arrived from Western Europe. We are repairing all kind of cars. We provide the best services and the best solutions to fix the car in time and save your money. All works in one place: engine repairs, transmission repairs, electrical repairs, suspension repairs etc. We work with most of European brands such as Bentley, Rolls Royce, Mercedes, BMW, VAG group, Ferrari, Lamborghini and others.


CARSTARS Garage offers a free carwash to each customer with every service visit. We provide deep cleaning services for free with each body restoration service. Ceramic coating is chargable, but we provide 20% discount to our loyal costumers.

Carstars Garage in Dubai is the best place to fix, repair or modify your car!

50% off for A/C System check and refill

Carstars Garage in Dubai is offering 50% discount for A/C system check up and A/C gas refill for each customer who writes a review in Google and likes our Facebook and Instagram pages.

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21 April 2020


21 April 2020

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