Best practice: A/C service using the flushing function

The NUNCHI CLIMATE ACEntre20+ allows the workshop to go beyond a conventional recovery, vacuum and recharge service.

By combining normal A/C servicing with refrigerant flushing and compressor-oil management, the technician can perform a more comprehensive service designed to remove old oil and contaminants from suitable parts of the A/C circuit.

A correct service procedure is especially important when working with modern A/C and heat pump systems, hybrid vehicles and electric vehicles.

Important: Always follow the vehicle manufacturer’s service information. Refrigerant type, oil type, oil quantity, flushing procedure, valve positions and component restrictions vary between vehicles.

1. IDENTIFY THE VEHICLE AND REFRIGERANT

Before connecting the ACEntre20+:

• Identify the vehicle.
• Confirm the specified refrigerant.
• Confirm the correct refrigerant charge quantity.
• Identify the required compressor oil.
• Check the specified oil quantity.
• Determine whether the vehicle uses a conventional or electric compressor.
• Check whether the vehicle has an A/C system or a more complex heat-pump system.
• Check the manufacturer’s flushing requirements and restrictions.

Never assume the refrigerant or oil specification based only on the age of the vehicle.

2. PERFORM A VISUAL INSPECTION

Inspect the A/C system before beginning the automatic service.

Check:

• Service ports and caps
• Refrigerant hoses and pipes
• Compressor
• Condenser/gas cooler
• Receiver drier or accumulator
• Expansion devices
• Visible oil traces
• Signs of refrigerant leakage
• Signs of previous repairs
• Damaged wiring or connectors
• Cooling fans
• Airflow restrictions through the heat exchangers

If there is evidence of a major leak or mechanical compressor failure, investigate the cause before simply recharging the system.

3. CHECK SYSTEM OPERATION

If the system can be operated safely, perform an initial functional test.

Record:

• Ambient temperature
• Vent temperature
• High-side pressure
• Low-side pressure
• Compressor operation
• Cooling fan operation
• Airflow
• Any fault codes or abnormal operating conditions

This provides a useful before-service reference that can later be compared with the system’s performance after servicing.

4. CONNECT THE ACENTRE20+

Connect the high- and low-pressure service hoses to the correct vehicle service ports.

Before beginning:

• Confirm that the machine contains the correct refrigerant.
• Check available refrigerant quantity.
• Check the condition of the machine filters.
• Check the waste-oil container.
• Check the fresh-oil container where applicable.
• Confirm that the correct oil is being used.
• Make sure the service hoses and couplings are in good condition.

Prevent Oil Cross-Contamination

Oil control is particularly important when the same workshop services both conventional vehicles and vehicles with high-voltage electric compressors.

Never introduce an incompatible oil into an electric compressor system.

5. RECOVER THE REFRIGERANT

Begin the refrigerant recovery process and allow the ACEntre20+ to complete the full recovery cycle.

Record the quantity of refrigerant recovered.

Comparing the recovered quantity with the manufacturer’s specified charge can provide useful diagnostic information.

A significantly low recovered quantity may indicate:

• Refrigerant leakage
• Previous incorrect charging
• Previous repair
• Refrigerant loss from the system
• 6. MEASURE THE RECOVERED OIL

Inspect and record the quantity and condition of oil removed during recovery.

Look for:

• Discoloration
• Metal particles
• Abnormal contamination
• Excessive oil
• Signs of moisture
• Unusual smell or degradation

The condition of the recovered oil can provide valuable information about the internal condition of the A/C system.

7. DECIDE WHETHER FLUSHING IS REQUIRED

Flushing should be performed for a reason rather than automatically on every vehicle.

Flushing may be recommended when:

• Compressor oil is being replaced.
• The wrong oil has been used.
• Oil contamination is suspected.
• A compressor has been replaced.
• Excessive oil is suspected.
• The system has been opened for major repairs.
• Contamination is present.
• Conversion to the correct oil specification is required.
• The manufacturer’s service procedure requires flushing.

For routine maintenance on a clean, correctly operating system, flushing may not always be necessary.

8. PREPARE THE SYSTEM FOR FLUSHING

This is one of the most important parts of the procedure.

Not every A/C component should be flushed.

Depending on the vehicle and manufacturer procedure, components that may need to be isolated, bypassed or replaced can include:

• Compressor
• Expansion valve
• Orifice tube
• Receiver drier
• Accumulator
• Certain solenoid valves
• Electrically controlled valves
• Components containing fine restrictions

Receiver driers, desiccant elements and accumulators should generally be treated according to the vehicle manufacturer’s replacement instructions rather than regarded as normal flushing passages.

9. OPEN ELECTRONIC VALVES WHEN REQUIRED

Modern A/C and heat-pump systems can contain several electronically controlled refrigerant valves.

If a valve remains closed, refrigerant may not circulate through the intended part of the circuit during flushing.

Depending on the vehicle, it may therefore be necessary to use a diagnostic scan tool to command certain valves into the required service position.

Always follow the vehicle manufacturer’s specified service mode and valve-opening procedure.

This is particularly important on hybrid and electric vehicle heat-pump systems.

10. PERFORM THE REFRIGERANT FLUSH

The ACEntre20+ uses refrigerant as the flushing medium.

During the flushing process, refrigerant circulates through the appropriate section of the A/C circuit to help transport:

• Old compressor oil
• Residual oil
• Fine contamination
• Suspended particles
• Unwanted residues

out of the circuit.

Major Advantage

No separate flushing chemical needs to be introduced into the sections being refrigerant-flushed.

This reduces the risk of leaving incompatible flushing-fluid residue inside the system.

11. MONITOR THE FLUSHING PROCESS

Do not treat flushing as simply an automatic button-push operation.

Monitor:

• Oil being removed
• Contamination
• Flushing progress
• Machine operation
• Quantity of material recovered

If significant contamination continues to appear, additional flushing cycles may be necessary.

The objective is not simply to complete a flushing cycle.

The objective is to achieve a clean A/C circuit suitable for reliable operation.

12. HEAVY COMPRESSOR CONTAMINATION

If a compressor has suffered severe mechanical failure, additional procedures may be required.

Metal particles or other debris can become trapped inside:

• Microchannel condensers
• Parallel-flow condensers
• Expansion devices
• Filters
• Small refrigerant passages
• Complex heat exchangers

Some components may not be possible to clean reliably.

Do not assume that flushing can repair every contaminated system.

Where required by the vehicle or component manufacturer, contaminated components should be replaced.

13. REPLACE THE RECEIVER DRIER / DESICCANT WHEN REQUIRED

Whenever the system has been open for an extended period or following major repairs, evaluate the receiver drier, accumulator or desiccant element according to manufacturer requirements.

The desiccant’s purpose is to absorb moisture.

Once its moisture capacity has been compromised, flushing does not restore the desiccant.

14. PERFORM A DEEP VACUUM

After flushing and completing all repairs, evacuate the A/C system thoroughly.

The vacuum process helps remove:

• Air
• Moisture
• Residual refrigerant vapor
• Non-condensable gases

Do not shorten the vacuum process simply to reduce service time.

Systems that have been open for an extended period may require a longer evacuation.

15. PERFORM A VACUUM LEAK TEST

After reaching the required vacuum level, allow the ACEntre20+ to perform the appropriate vacuum hold/leak test.

A significant loss of vacuum can indicate:

• Leakage
• Moisture remaining in the system
• Incorrect service connection
• Component or seal problems

Remember that a vacuum test alone does not detect every possible refrigerant leak.

16. ADD THE CORRECT COMPRESSOR OIL

Only introduce the manufacturer-specified oil type and quantity.

Depending on the vehicle, this may include:

• PAG
• Double-end-capped PAG
• PAG YF
• POE
• PVE
• Other manufacturer-specified oil
• Never mix oils simply because they have similar viscosity.

For electric compressors, incorrect oil can affect electrical insulation as well as lubrication.

17. CHARGE THE EXACT REFRIGERANT QUANTITY

Charge the vehicle according to the manufacturer’s specified refrigerant quantity.

Modern A/C and heat-pump systems can be sensitive to incorrect charge levels.

Both undercharging and overcharging can reduce system performance and may contribute to component problems.

Always charge by weight, not simply according to pressure readings.

18. RUN THE SYSTEM AFTER SERVICE

After charging, start the vehicle and operate the A/C system according to the manufacturer’s test conditions.

Allow the system to stabilize.

Check:

• High-side pressure
• Low-side pressure
• Vent temperature
• Ambient temperature
• Compressor operation
• Cooling fan operation
• Refrigerant circulation
• Unusual noise
• System fault codes

For heat-pump systems, test the relevant cooling and heating modes when required.

19. COMPARE BEFORE & AFTER RESULTS

Compare the original measurements with the post-service results.

Before Service → After Service

Compare:

• Refrigerant quantity
• Oil condition
• High-side pressure
• Low-side pressure
• Vent temperature
• Compressor behavior
• System performance

This provides a much better assessment of the service than simply confirming that the machine completed its automatic program.