Flushing an air conditioning system

Air Conditioning System Flushing for Optimal Cleaning

When working on a vehicle's air conditioning system, when it comes to replacing a component, the flushing process is the most important step to finish the repair and restore the system to full working order.

When working on a vehicle’s air conditioning system, when it comes to replacing a component, the flushing process is the most important step to finish the repair and restore the system to full working order.

But what is flushing?

Flushing is an operation that removes used oil and all the solid contaminants from inside the components of a vehicle’s air conditioning system.

A clean air conditioning system is a healthy air conditioning system.

When should I flush an air conditioning system?

There are many possible scenarios when you might need to perform a flushing operation. You might have detected impurities in the system, need to change the compressor or have some fault with another component.

If you are replacing the compressor, you will need to flush the system once it has been reassembled and sealed to remove any impurities such as iron filings from inside the circuit. In fact, this can easily be caused by a worn dehydrator or hose. In this case, you will need to choose the right flushing method.

Two flushing methods are possible to achieve good results – flushing with a solvent or flushing in liquid phase. Flushing with a solvent is particularly suitable for a sealed compressor. Flushing in liquid phase, on the other hand, is recommended for cases where a dehydrator or hose has deteriorated.

How to flush a system

Flushing in liquid phase:


This method consists of circulating liquid refrigerant around the system. This technique is both economic and ecological, allows to remove oil and solid particles from the system and can even remove the residues from flushing solvents. However, it is not suitable for cases where the compressor is not sealed.

It is important to follow 6 key steps:

  • Step 1: Recover all refrigerant in conformance with regulations.
  • Step 2: Disconnect the system and remove all components that should not be flushed.
    The components that should not be flushed include: pressure reducer, calibrated orifice, compressor, dehydrator and parallel flow condenser.
    WARNING: the dehydrator should be changed with each flush and the compressor should never receive flushing liquid nor ever be flushed.
  • Step 3: Disassemble the components to carry out the flushing operation. To achieve the best results, flush each component separately. You will not only achieve better results but it will also be faster.
    The following components should be flushed:

        • The hose from the compressor to the condenser
        • The condenser (apart from a parallel flow condenser)
        • The hose from the top of the condenser
        • The evaporator
  • Step 4: Begin flushing: Connect the recovery, recycling and flushing unit to the low pressure port. The liquid refrigerant enters through the high pressure port. Purge the air from the system and start the recovery unit.
  • Step 5: Reassembly: Having flushed the system, the filter-dehydrator and the pressure reducer (or calibrated orifice) should be immediately replaced.
  • Step 6: Bleeding, checks and recharging
    It is important to bleed all air out of the system. This will prevent the formation of vapour and ensure that the lubricant can circulate freely.

Flushing with a solvent:

Flushing with a solvent

This method consists of circulating a solvent around the air conditioning circuit. This makes it possible to remove humidity and acidity from the system.

The solvent is added to the system under pressure and circulates around the system thanks to a pneumatic pump. The chemical reaction of the solvent absorbs all humidity and acidity.

What you must not forget

It is important, once the flushing operation is complete, the check that the circuit does not have any leaks once it has been recharged with refrigerant. This check can be carried out using a leak detector.

There you have it. Your air conditioning system has been flushed and once more ready to be used.

Don’t forget that flushing is obligatory when replacing any component (particularly when the compressor is sealed).

Source : SNDC

SNDC designed and supplies air conditioning, heating, filtration and pressurisation systems for vehicle cabins


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