Refrigerant Circuit, Flushing With R134A Refrigerant: Notes
The refrigerant circuit should be flushed with refrigerant R134a
- There is dirt or other contamination in the refrigerant circuit.
- Vacuum reading is not maintained when evacuating a leak-free refrigerant circuit (pressure build-up due to moisture in refrigerant circuit).
- The refrigerant circuit has been left open for longer than normal (for example, after a collision).
- If pressure and temperature measurements in the refrigerant circuit indicate the likelihood of moisture in the refrigerant circuit.
- If there is any uncertainty as to how much refrigerant oil is in the refrigerant circuit. If the A/C compressor should be reinstalled, the refrigerant oil should be drained from the A/C compressor via the block connections if this is the case. To facilitate this, the ribbed belt pulley or A/C clutch plate on the A/C compressor should be rotated by hand. After flushing, the entire quantity of refrigerant oil specified by the Vehicle-Specific Service Information must be added to the refrigerant circuit (50 grams directly into the A/C compressor). Pay attention to the additional oil quantity for the second evaporator.
- A/C compressor had to be replaced due to internal damage (for example, noise or no output).
- It is stipulated by the vehicle-specific Service Information following the replacement of certain components.
- Another A/C compressor with a different refrigerant oil should be installed.
Required Tools
- A/C Service Station with flushing device or Air Conditioning Flush Tool :VAS6337 . The auxiliary function "Flush refrigerant circuit with refrigerant R134a" and the refrigerant circuit flushing device required for it are present on these A/C service stations. Refer to Special Tools and Equipment Catalog.
- Refrigerant Circuits Adapter Set 1 :VAS6338/1 . Refer to ADAPTER FOR ASSEMBLING FLUSHING CIRCUIT and Special Tools and Equipment Catalog
- Refrigerant Circuits Adapter Set 2 :VAS6338/50 . Refer to ADAPTER FOR ASSEMBLING FLUSHING CIRCUIT and Special Tools and Equipment Catalog.
If neither of the two A/C service stations listed above are available for use in the workshop, the A/C Service Station with Flushing Device :VAS6336/1 or Air Conditioning Flush Tool :VAS6337/1 can also be used to flush the refrigerant circuit, depending on the A/C Service Station version (at least 7 kg refrigerant R134a in refrigerant bottle). However, the flushing procedure must then be performed manually. Refer to Flushing Procedure Sequence (sequence occurs automatically according to the program) .
For vehicles with threaded connections on the refrigerant circuit, A/C Adapter Set - Adapter 1 :VAG1785/1 through A/C Adapter Set - Adapter 2 :VAG1785/8 from the Refrigerant Circuits Adapter Set 1 :VAS6338/1 or Refrigerant Circuits Adapter Set 2 :VAS6338/50 may be used. For vehicles with threaded connections on the A/C compressor and on reservoir, two of the A/C Adapter Set - Adapters 8 :VAG1785/8 are required.
A Hose :VAS6338/31 with 5/8 -18 UNF connections and large inner diameter can be found in the adapter sets in order to be able to bridge components (it is commercially available).
Preliminary work
-- Discharge the refrigerant circuit. Refer to REFRIGERANT CIRCUIT, DISCHARGING WITH A/C Service Station .
-- Remove the A/C compressor. Refer to Heating, Ventilation and Air Conditioning.
On a vehicle with a restrictor and reservoir.
-- Remove the restrictor (vehicle-specific) and reconnect the refrigerant pipes with each other. Refer to Heating, Ventilation and Air Conditioning.
-- Remove the reservoir (vehicle-specific) (refer to Heating, Ventilation and Air Conditioning) and connect the refrigerant pipes to each other (to do this, use the adapters and the Hose :VAS6338/31 from Refrigerant Circuits Adapter Set 1 :VAS6338/1 ). Refer to ADAPTER FOR ASSEMBLING FLUSHING CIRCUIT .
The reservoir could be flushed, but it requires too much refrigerant due to its large volume. When this refrigerant is evacuated, the reservoir ices up severely and this prolongs the extraction process significantly.
Vehicle with expansion valve and receiver/dryer
-- Remove the receiver/dryer (refer to Heating, Ventilation and Air Conditioning) (vehicle-specific; not required for all vehicles) and connect the refrigerant pipes to each other (for this, use adapters and Hose :VAS6338/31 ). Refer to ADAPTER FOR ASSEMBLING FLUSHING CIRCUIT .
-- Remove the expansion valve (vehicle-specific) (refer to Heating, Ventilation and Air Conditioning) and install the adapter for it. Refer to ADAPTER FOR ASSEMBLING FLUSHING CIRCUIT .
If no suitable adapter for the expansion valve is available in Refrigerant Circuits Adapter Set 1 :VAS6338/1 or Refrigerant Circuits Adapter Set 2 :VAS6338/50 , the removed expansion valve can also be drilled open (the old expansion valve must be replaced with a new one).
Ignore item -3-.
Make sure when drilling that the flow holes -2 and 4- in the expansion valve -1- are offset to each other.
If not paying attention while drilling, the sealing surface on the expansion valve -1- could be damaged and then the expansion valve may no longer be used when installing the flushing circuit.
Several components are to be removed from the expansion valve before drilling open.
There are different versions of the expansion valves. For version -A-, components -B, C and D- must be removed. Then separate the regulating element -E- from component -D-. Then drill open the expansion valve in area -F- using a suitable drill bit (6 mm).
For version -G-, components -H-, -I- and -K- must be removed and then drill open area -L- using a suitable drill bit (6 mm).
Clean the drilled open expansion valve of residue from the work (shavings).
Re-install the components -B, C and D- for version -A-, or component -H- for version -G-.
For vehicles with two evaporators, the circuit to the second evaporator must be disconnected from the circuit of the first evaporator and must be flushed via a separate work procedure. Refer to Heating, Ventilation and Air Conditioning and ADAPTER FOR ASSEMBLING FLUSHING CIRCUIT .
Shut-Off Valve, Drilling Open
Two shut-off valves are required for flushing the refrigerant circuit. If the Shut-Off Valve :VAS6338/42 is not available to flush the refrigerant circuit, than a shut-off valve is to be drilled out, for example.
Remove the solenoid coil -A- and the solenoid valve -B- before drilling open.
Drill open the shut-off valve -C- using a suitable drill bit (drill bit diameter 5.0 mm, for example).
Clean the shut-off valve -C- from the shavings produced by drilling -D-.
Re-install the solenoid valve -B- with the appropriate seal -E- in the drilled open shut-off valve -C-.
Flushing
-- Check the refrigerant quantity in the refrigerant cylinder. There must be at least 7 kg of refrigerant R134a.
If necessary, switch on the heater installed on the refrigerant cylinder for 30 minutes before the first flushing procedure. This increases pressure in the refrigerant cylinder and accelerates charging of the flushing circuit.
-- Drain the A/C Service Station used oil container.
-- Connect the supply hose (high pressure side) of A/C Service Station to the low pressure line leading to the A/C compressor (line with larger diameter) using an adapter. Refer to ADAPTER FOR ASSEMBLING FLUSHING CIRCUIT .
-- Connect the return hose (low pressure- or intake side) of the A/C Service Station to the output of refrigerant circuit flushing device.
-- Connect the input on the refrigerant circuit flushing device to the high pressure line leading to the A/C compressor (line with smaller diameter) using an adapter. Refer to ADAPTER FOR ASSEMBLING FLUSHING CIRCUIT .
Components are always (with the exception of the electrically-driven A/C compressor) flushed in the opposite direction of refrigerant flow when the A/C system is operating. Refer to FLUSHING CIRCUIT BLOCK DIAGRAMS .
While flushing, contaminants from the refrigerant circuit enter the refrigerant circuit flushing device and the A/C Service Station and are absorbed by the filters and dryers installed there. Depending on the contaminant, these components are to be replaced in shorter intervals according to the operating instructions for the A/C Service Station or refrigerant circuit flushing device.
The filter in the refrigerant circuit flushing device depends on the type and degree of contamination in the flushed refrigerant circuit. It should be replaced after two flushing cycles, at the most. If a heavily contaminated refrigerant circuit is flushed (the refrigerant oil from the refrigerant circuit is black and viscous, or there are many shavings in the refrigerant circuit), the filter should be replaced after flushing the refrigerant circuit. With a refrigerant circuit heavily contaminated in this way, it is wise to flush the refrigerant circuit again after changing the filter.
Depending on the type of contamination, dirt (old refrigerant oil and abraded material from the A/C compressor) is deposited on the viewing glass(es) of the refrigerant circuit flushing device. Clean the viewing glass(es) after flushing and flush the refrigerant circuit once more with one flushing procedure as a check.
Fluid refrigerant cannot be directed with the necessary speed through the expansion valve, restrictor and desiccant bag of certain receiver/dryers. Therefore, these components must be removed and replaced by an adapter. Refer to Heating, Ventilation and Air Conditioning.
Adapters for connecting the A/C Service Station and for bridging certain components of refrigerant circuit. Refer to ADAPTER FOR ASSEMBLING FLUSHING CIRCUIT .
-- Switch on the A/C Service Station and flush the refrigerant circuit (duration for one flushing cycle with three flushing procedures is approximately 1 to 1.5 hours for approximately 4 kg of refrigerant R134a).
Flushing the refrigerant circuit is to be performed according to the A/C Service Station operating instructions.
Depending on the A/C Service Station version, the used oil container holds only approximately 125 cm 3 of refrigerant oil. In the event a system with a larger refrigerant oil quantity must be flushed, it may be necessary to empty the used oil container after the first flushing procedure of a flushing cycle.
Observe the refrigerant which flows back from the refrigerant circuit. The refrigerant circuit is only clean when the refrigerant flows clear and completely colorless through the viewing glass(es) on the refrigerant circuit flushing device in the A/C service station.
When flushing, the entire amount of refrigerant oil is washed out of the refrigerant circuit (except for minor remains which can be disregarded).
If contamination is especially severe, it may be necessary to perform the flushing cycle twice (two flushing cycles with three flushing operations each). Before the second flushing cycle, the filter on the flushing device must be replaced.