What is a condenser fan

The automotive air conditioning system (2) - refrigeration circuit and components


Cooling circuit / components of the automotive air conditioning system


Main components of the automotive air conditioning system

Scheme of automotive air conditioning systems

The following schemes illustrate the refrigeration cycle of an air conditioning system.


The refrigeration principle cycle

Circuit diagram of the refrigeration cycle

Tasks Components of vehicle air conditioning



The numbers refer to the climate diagram above

TheAir conditioning compressor does the job that is already in the evaporator sucking in and compressing evaporated refrigerants.

The refrigerant is thus brought to a different pressure and temperature level (approx. 15 bar / 56 ° C). The refrigerant gases are then passed on towards the condenser at high pressure and high temperature.

Many compressors have a magnetic coupling so that they can be switched on as required.

Piston and swash plate compressors are used. Some swash plate compressors have a variable displacement. Switching on or off is not necessary here.


Condenser (2) with fan

in thecapacitor (Condenser) the gaseous, superheated refrigerant is brought to a condenser temperature chilled and liquefied. Since heat is withdrawn from the refrigerant when it liquefies, like any other substance, the condenser has to transfer this heat to a surrounding cooling medium (air or water).

The Condenser fan has the task of under all operating conditions of the vehicle for sufficient ventilation of Capacitor to care. Sufficient ventilation of the condenser keeps the refrigerant pressure low on the high pressure side. The condenser fan is switched on and off by the pressure switch depending on the refrigerant pressure. Cooling coil condensers are used.

Filter drier (3)

in theFilter drier becomes the refrigerant cleaned and dried.

The refrigerant is filtered with each cycle. The refrigerant is freed of suspended matter in the dryer bottle (e.g. abrasion parts from the compressor). In addition, hygroscopic globules remove moisture (water) from the refrigerant in order to protect the system from corrosion and malfunctions. And thirdly, the refrigerant is stored upstream for onward transport to the expansion valve (storage function).

The dryer bottle is a wear part and must be changed at regular intervals (according to HELLA every 2 years) or when the system has been opened.

Expansion valve (4)

TheExpansion valve injects the refrigerant one, it can expand. The expansion valve is therefore the point where the refrigerant expands in the evaporator and cools it down.

The pressure drops sharply (approx. 2.5 bar). Thermostatic expansion valves are precision devices, the task of which is to always supply the evaporator with the amount of refrigerant that evaporates under the respective working conditions. You should thus maintain the balance between inflow and suction in every operating state in order to always fully utilize the heat-transferring evaporator surfaces. It also prevents the compressor from sucking in liquid refrigerant.

Throttle (alternative)

There are air conditioners that don't Expansion valve own a fixed one instead throttle (Orifice). The throttle is a bottleneck in the refrigerant circuit, directly in front of the evaporator. This "throttles" the flow of the refrigerant. The liquid refrigerant is sprayed into the evaporator through the throttle. The refrigerant is warm under high pressure upstream of the throttle. The rapid pressure drop occurs when the throttle is passed. The refrigerant becomes cold at low pressure. The throttle thus forms the "separation point" between
High pressure and low pressure side in the refrigerant circuit.

In air conditioning systems with throttle control, there is instead of the liquid container in the high pressure side
a collecting container in the low pressure side
installed. It serves as a storage container and as protection for the compressor (liquid hammer).

All other components are identical to the
Circuit with expansion valve.

Evaporator (5) with interior fan (6)

By adding heatthe refrigerant evaporates in the Evaporator, the air is getting cold. The task of the evaporator is to ensure the exchange of thermal energy between the outside air and the refrigerant over the largest possible area. The refrigerant in the evaporator needs thermal energy in order to be able to evaporate. This thermal energy is extracted from the outside air via the surface of the evaporator.

The Interior fan has the task of constantly supplying fresh and warm outside air to the evaporator. If the interior fan fails, the evaporator cannot be prevented from icing up. When the air conditioning system is switched on, it must be ensured that at least the first fan level of the interior fan is activated.

Refrigerant oil

A special oil - refrigerant oil - that is free of contaminants such as sulfur, wax and moisture, is required to lubricate all moving parts in the air conditioning system. It must be compatible with the refrigerant itself, as part of it mixes with the refrigerant and runs along in the refrigerant circuit and must not attack the seals in the system.
No other oils should be used as they will lead to copper plating, coking and the formation of residues. Premature wear and tear and destruction of the moving parts would be the result.

The refrigerant oil can also only be matched to a specific type of compressor. So-called universal oils are not advisable, the compressor manufacturers reject any guarantee or goodwill performance when using unapproved oils.

The refrigerant oil for R134a is PAG = poly-alkylene-glycol

Due to its chemical properties, the refrigerant oil must not be disposed of together with engine oil or gear oil.

Influencing variables of the refrigeration cycle

  • The temperature of the outside air

  • The speed of the engine

  • The fill level of the air conditioning system

  • The fan level of the interior fan

  • The temperature of the engine compartment.

  • The humidity of the incoming outside air

Electrical components automotive air conditioning

1 switch for air conditioning6 thermal switches for fans for coolant
2 Pressure relief valve on the compressor7 sender for evaporator temperature
3 fans for coolant8 fresh air blower
4 pressure switches for air conditioning9 Engine control unit
5 senders for coolant temperature10 magnetic coupling

Electric components


The most common faults in the refrigeration cycle

  • Overcrowding
  • Underfill
  • Leak in the refrigeration circuit
  • A blockage in the refrigeration circuit
  • Incorrect thermostat setting (icing)
  • Air-side blockage on the condenser
  • Failed or incorrectly rotating condenser fan
  • Too much moisture in the refrigeration circuit.

Another diagram with air distribution

1 = compressor

2 = condenser with fan

3 = trinary switch

4 = filter drier

5 = expansion valve

6 = evaporator

7 = heat exchanger

8 = fan



Source: Bosch, VW, Meinburk Climate Course

Author: Johannes Wiesinger

edited: 08/12/2020

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