Refrigerant Circuit, Flushing with Refrigerant R134a: Notes

WARNING: This page does not describe the selected car, but rather 17 other vehicles, including the 2009 Audi S4, 2009 Audi A4, 2008 Audi S4, 2008 Audi RS 4, and 2008 Audi A4. However, it is still accessible from the selected car via links, so may be relevant.

Flush refrigerant circuit using refrigerant R134a in order to force out moisture and other contaminants (e.g. shavings from a malfunctioning compressor) as well as old refrigerant oil as efficiently as possible, without wasting refrigerant, without the need for extensive assembly work and without endangering the environment.

Flush the refrigerant circuit:

In the event of dirt or other contamination in the circuit.

If vacuum reading is not maintained on evacuating a leak-free refrigerant circuit (pressure build-up due to moisture in refrigerant circuit).

If refrigerant circuit has been left open for longer than normal (e.g. following an accident).

If pressure and temperature measurements in the refrigerant circuit indicate the likelihood of moisture.

In the event of doubt about the amount of refrigerant oil in the circuit.

The A/C compressor had to be replaced on account of internal damage (e.g. noise or no output).

If stipulated by the vehicle-specific repair manual following replacement of certain components.

Tools required

A/C service station with flushing equipment VAS 6336 or A/C service station with flushing equipment VAS 6337 (these A/C service stations include the additional function for "flushing the refrigerant circuit" and the required equipment for flushing refrigerant circuits) → Workshop equipment and special tools catalog

Adapter case for VW/Audi passenger cars VAS 6338/1 → Adapter for Assembly of Flushing Circuits and → Workshop equipment and special tools catalog

NOTE:

If there is neither of the mentioned A/C service stations, it is possible to flush the refrigerant circuit using flushing equipment for refrigerant circuits VAS 6336/1 or flushing equipment for refrigerant circuits VAS 6337/1 depending on the A/C service station used, flushing must then be performed manually. → Process of flushing (process is performed automatically according to the A/C service station program)
On vehicles with threaded connections to the refrigerant circuit, the adapters V.A.G 1785/7 and adapters V.A.G 1785/8 from the adapter case for VW/Audi passenger cars VAS 6338/1 can be used; on vehicles with threaded connections to compressor and to reservoir, the adapter V.A.G 1785/8 is needed twice.
There is also a fill hose VAS 6338/31 with connections 5/8 -18 UNF and large inner diameter in short version (commercially available) included in the adapter case for VW/Audi passenger cars VAS 6338/1.

Preparation

Discharge A/C refrigerant system.

Remove compressor → 87 - Air conditioning

On a vehicle with restrictor and reservoir

Remove restrictor (vehicle-specific) and reconnect lines → 87 - Air conditioning

Remove reservoir (vehicle-specific) and reconnect the lines (use adapters and fill hose VAS 6338/31 from the adapter case for VW/Audi passenger cars VAS 6338/1 ) → Adapter for Assembly of Flushing Circuits , → 87 - Air conditioning

NOTE:

The reservoir could be flushed but because of its large internal volume it will take too much refrigerant, the reservoir would ice-up too much when extracting the refrigerant, the refrigerant would evaporate too slowly and extraction would be extended too much.

On a vehicle with expansion valve and fluid reservoir

Remove fluid reservoir (vehicle-specific) and reconnect the lines (use adapters and fill hose VAS 6338/31 from the adapter case for VW/Audi passenger cars VAS 6338/1 ) → Adapter for Assembly of Flushing Circuits , → 87 - Air conditioning

NOTE:

The fluid reservoir can be flushed depending on the version (remove dryer cartridge if necessary) → Adapter for Assembly of Flushing Circuits , → 87 - Air conditioning
The fluid reservoir connected to the condenser (e.g. on model Audi A3 from model year 2004) remains installed during flushing (it can be flushed due to its design and is only replaced after flushing) → Adapter for Assembly of Flushing Circuits and → 87 - Air conditioning
Remove dryer cartridge from vehicles with dryer partridge in fluid reservoir that is connected to the condenser (vehicle-specific), and re-seal opening on fluid reservoir → 87 - Air conditioning
Remove expansion valve (vehicle-specific) and install one adapter from the adapter case for VW/Audi passenger cars VAS 6338/1 → Adapter for Assembly of Flushing Circuits , → 87 - Air conditioning .

NOTE:

If there is no appropriate expansion valve in the adapter case for VW/Audi passenger cars VAS 6338/1 , the removed expansion valve may be drilled (the old expansion valve will be replaced in most cases and therefore is no longer needed).
Remove regulating element before drilling and drill expansion valve e.g. using a suitable drill (diameter of drill e.g. 6 mm).

Fig 1: Expansion Valve Components

Courtesy of VOLKSWAGEN UNITED STATES, INC.

Expansion valves are available in different versions and designs. For version - A - , there must be removed components - B - , - C - and - D -. Then remove component part - E - (regulating element) from component - D -. Drill expansion valve in area - F - using suitable drill.

For version - G - , parts - H - , - I - and - K - must be removed and then drill area - L - using suitable drill.

Clean drilled expansion valve from drilling remains (shavings)

Install parts - B - , - C - and - D - for version - A - or - H - for version - G -

NOTE:

On vehicles with two evaporators, disconnect second evaporator circuit from first evaporator circuit and flush separately → 87 - Air conditioning and → Adapter for Assembly of Flushing Circuits .

Flushing

Check amount of refrigerant in A/C service station, there must be at least 7 kg of refrigerant R134a

NOTE:

If necessary, switch on heating installed in A/C service station for the refrigerant container before first flushing (to increase the pressure in the refrigerant container) and switch off before first extraction during flushing.
Drain container for used oil on A/C service station
Connect supply line (high pressure side) of A/C service station to low pressure line to compressor (line with larger diameter) using an adapter → Adapter for Assembly of Flushing Circuits
Connect return line (low pressure or intake side) of the A/C service station to the flushing equipment output of refrigerant circuits
Connect the input of the flushing equipment for refrigerant circuits to the high pressure line toward compressor (line with smaller diameter) using an adapter → Adapter for Assembly of Flushing Circuits

NOTE:

Always flush components in direction opposite to refrigerant flow with A/C system operated. → Block Diagrams for Flushing Circuits
When flushing, impurities get from the refrigerant circuit to the flushing equipment and to the A/C service station, and are retained in the filter and dryer installed there. Depending on the impurities, these components must be replaced in shorter intervals corresponding to the operating instructions on the A/C service station or the flushing equipment for refrigerant circuits. (filter of flushing equipment for refrigerant circuits after approx. 5 to 10 flushing cycles, depending on impurities of flushed refrigerant circuits).
Depending on the kind of impurity, dirt is deposited at the sight glass of the flushing device for refrigerant circuits (old refrigerant oil and shavings from the compressor). Clean the sight glass after flushing if necessary, and flush the refrigerant circuit again for checking (one cycle is sufficient).
Liquid refrigerant cannot be led through the expansion valve, restrictor and dryer bag of certain fluid reservoirs at an appropriate speed, therefore these components must be removed and replaced by adapters if necessary → 87 - Air conditioning
Adapters for connecting the A/C service station and for bridging certain components of the refrigerant circuit → Adapter for Assembly of Flushing Circuits
Switch on the A/C service station and flush the refrigerant circuit (duration for one flushing cycle with three flushing procedures is approx. 1 to 1.5 hours)

NOTE:

Flushing procedure must be performed according to the operating instructions of the A/C service station
Depending on the version of A/C service station, the reservoir for used oil contains only approx. 125 cm ³ refrigerant oil; in case it should be necessary to flush a system with a larger amount of refrigerant oil, it may be necessary to drain the reservoir for used oil after the first flushing procedure of a flushing cycle.
Observe the refrigerant that flows back from the refrigerant circuit into the A/C service station; only when the refrigerant flows clear and completely colorless through the sight glass of the flushing equipment for refrigerant circuits into the A/C service station, the refrigerant circuit is cleaned.
When flushing, the complete amount of refrigerant oil is washed out of the refrigerant circuit (except for minor remains e.g. in the evaporator which can be neglected).
If very dirty, it may be necessary to repeat the flushing procedure (i.e. two flushing cycles with three flushing procedures each).