Latest News:

autotechnician - serving the independent workshop - logo

AC System Maintenance: System flushing

By autotech-nic on July 7, 2017
To perform properly, the AC system must be clinically clean inside the loop. Refrigerant and lubricant working in high temperatures and pressures, as well as components with precise mechanisms (compressor, expansion devices), require cleanliness for optimal operation. Flushing is considered one of the most basic and important service procedures, and is highly recommended by AC experts, as well as the major manufacturers of compressors. Flushing is also the only way to determine the proper level of lubricant recommended for the given compressor/vehicle model.
Impurities, refrigerant and oil contaminants, or improper use of additives, can quickly cause clogs in the thin system channels of the receiver dryer, condenser tubes, expansion devices, and the compressors’ ECV/MCV valves. System stoppages will lead to a decrease in the system’s performance and cause serious pressure increases, resulting in an abnormal temperature load on the compressor.
Contaminants and moisture also affect lubricating characteristics of the oil. Improper lubrication has an instant negative effect on a compressor’s mechanical parts, exposing it to seizure. Missing, diluted or improper oil will lead to irreversible compressor failures.
Recommended solution
To avoid system performance-related problems and expensive repeat repairs, flush the system whenever it has been diagnosed with clogs, stoppages, receiver dryer failures or excessive or improper use of additives such us UV dye or ‘stop leaks’ agents.
Furthermore, always flush the system before installing a new compressor. Carbonised oil particles, metal chips and other impurities that caused the previous compressor to fail can quickly kill the new unit if the system was not flushed.
The only reliable way to determine the proper volume of the lubricant in the system during a service cycle is flushing and filling an empty system with the right type and volume of oil. Appropriate lubrication guarantees vitality and a long lifespan for the compressor.
Keep in mind that the following components should not be flushed: compressor (replace/bypass), expansion devices (bypass), receiver dryer/desiccant (replace). NB – in case of any suspicion of stubborn contamination inside the condenser/evaporator after flushing, the components should always be replaced.
Recommended flushing methods
Flushing detergent
A special flushing detergent is circulated throughout the loop using a dedicated flushing machine, or can be injected directly from a pressure container. This flushing method offers excellent cleaning properties by dissolving all sorts of particles, sludge, stubborn soil and residues.
Caution! The cleaning agent residues must be thoroughly removed after flushing and the circuit must be dried by vacuum.
Refrigerant & filling station
System is flushed by means of the R134a refrigerant circulated by the filling station. The station must be equipped with a flushing function, specially designed filters and a container to collect contaminants. This flushing method effectively cleans loose particles; however, it may not be effective for rinsing serious sludge and soils.
Caution! A vacuum must be pulled to dry the system after flushing.
Refrigerant directly from bottle
System is flushed by means of the R134a refrigerant circulated in the loop by heating up the bottle. An additional bottle for contaminated gas is needed, as well as an adapter and hose set ensuring proper system connection. This flushing method effectively cleans loose particles but may be ineffective for rinsing of serious sludge and soils.
Caution! A vacuum must be pulled to dry the system after flushing.
TIP: Use a supplementary glass inspection tool to spot possible contaminants circulating in the loop. This low-cost tool is highly recommended for an effective system contamination diagnostic, performed in various situations: before, during and after flushing.
View or download Nissens poster


About Autotechnician
Autotechnician is a magazine published nine times a year, delivering essential information to independent garage owners and technicians in the UK. Delivered both digitally and in print, autotechnician provides readers with technical, training, business advice, product and news, allowing our readers to keep up to date with information they need to run and work within a modern workshop.
Aftermarket Media Solutions Ltd, The Joiners Shop, Historic Dockyard Chatham, Kent ME4 4TZ
T: 01634 816 165
Company no. 09625886
linkedin facebook pinterest youtube rss twitter instagram facebook-blank rss-blank linkedin-blank pinterest youtube twitter instagram