Flushing the car AC system

Harmful substances and solids can form in the refrigerant circuit, leading to component damage. It is therefore absolutely essential that the air-conditioning system be flushed during repair work, and above all when exchanging the compressor. Here you can find out about the advantages and disadvantages of different flushing methods, as well as the effects of contaminants in the air-conditioning system.

The following technical information and practical tips have been compiled by HELLA in order to provide professional support to vehicle workshops in their day-to-day work. The information provided on this website is intended for suitably qualified personnel only.

Flushing the car AC system - The methods

Flushing air-conditioning systems is extremely important when repairs are carried out or if a compressor is damaged. The flushing process removes impurities and harmful substances from the air-conditioning circuit.

Flushing is necessary whenever professional repairs are carried out, as well as to prevent the need for further expensive repairs at a later date. In addition, flushing protects the warranty in the event of claims against the supplier and guarantees customer satisfaction.

However, do not flush compressors, expansion/throttle valves, or filter dryers and/or accumulators. Use adapters to bridge these components during the flushing process. Once the flushing process is complete, the valves and filters must be replaced.

The entire air-conditioning system must be flushed and the consumables and non-flushable components must be replaced when the compressor is replaced !

Car AC flush with refrigerant and service station

With its integrated flushing function, the air-conditioning service unit enables quick and cost-effective flushing of air-conditioning systems using liquid refrigerant R134a. An external flushing device and parts from a flushing adapter set must be used for this – both are available separately. Once the function has been started on the device, the vehicle air-conditioning system is filled with liquid refrigerant and then vacuumed again. This cycle should be carried out three times to achieve maximum cleaning effect.

Flushing with flushing liquid

In this method, the air-conditioning system is cleaned with a special flushing liquid (in combination with compressed air). After the flushing process, the system must be dried with nitrogen. This method is especially well suited for converting from R12 to R134a and is compatible with R1234yf air-conditioning systems. Even with the expensive R1234yf air-conditioning refrigerant, chemical flushing is a cost-effective alternative.

Note: Nitrogen must be used to dry the system after flushing with the flushing liquid.

Here, the connecting pipes and system components are blown out individually using nitrogen. When blowing out, it must be ensured that the maximum pressure of 12 bar is not exceeded.

Advantages and disadvantages of the flushing methods

Flushing method with refrigerant

System components are flushed using the air-conditioning service unit and an additional flushing device with filters and adapters.

Advantages

No costs for the flushing agent
No disposal costs for the flushing agent
Removes oil and loose particles of dirt
Method approved by various vehicle manufacturers

Disadvantages

Cleaning effect not optimal for persistent contamination
Filter element of the flushing device has to be replaced at regular intervals
During the application, the air-conditioning service unit is not otherwise available for use

Flushing method with flushing liquid

System components are flushed using an additional flushing device and a chemical solution. The remnants of the flushing agent must be removed and the system must be dried using nitrogen.

Advantages

Removes oil and loose and persistent particles
Excellent cleaning results

Disadvantages

Costs for the flushing agent
Disposal costs for the flushing agent

Effects of contamination

What contaminants can be removed by flushing? What are the consequences of these types of contamination?

Wear in the event of compressor damage

The material particles clog up expansion valves, throttle valves (orifice tubes), or multi-flow components (condenser, evaporator).

Humidity

Expansion valves and orifice tubes may ice up. Due to chemical reactions between the refrigerant/refrigerant oils and humidity, acids may form that make hoses and O-rings porous. The system components are then damaged by corrosion.

Elastomers (rubber)

The elastomer particles clog up expansion valves, orifice tubes, or multi-flow components.

Contaminated refrigerant oil or refrigerant

Acids may form as a result of contaminated refrigerant or the mixing of different refrigerants. The acids can make hoses and O-rings porous. Other system components can then be damaged by corrosion.

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