A dangerous mix

One thing is certain: contaminated refrigerant from vehicle HVAC systems can be explosive or easily flammable. But how can you tell if the gas is clean? And how do you remove it without hurting anybody or environment if it does happen to be contaminated? We’ll show you two methods for solving this problem.

A growing risk

The risk that an HVAC system contains contaminated refrigerant has increased. The reason is that since 1 January 2017, two different products have been on the market:

  • R 134a is used in vehicles that were registered before this date.
  • R 1234yf is used in all newly registered passenger cars and delivery vans up to 3.5 metric tonnes of permissible total mass.

Because two refrigerants are used, mix-ups can occur more easily. What’s more, R 1234yf is considerably more expensive than R 134a. This may in future lead to the tendency in certain markets to use other, non-approved refrigerants.

Forewarned is forearmed

That is why you should always analyse the refrigerant before commencing the service. Only extract the refrigerant in the usual way using the A/C service unit if the technical degree of purity is at least 92 or 95 per cent. If it is below this value, two other options are available.

Method 1: “Coolant on ice”


Contaminated refrigerant can be removed from the vehicle HVAC system using dry ice. In this case, you must place a recovery cylinder in a dry ice bath to bring the temperature down significantly. The resulting pressure difference is used to extract the gas mixture from the vehicle. Because this process does not generate sparks, nothing can catch fire.

But the method does have certain disadvantages: Dry ice (CO2) is toxic and because of its extremely low temperature (-78.5°C), it can immediately cause painful burn injuries to unprotected body parts. In addition, if you suspect that the refrigerant is contaminated, the service will be delayed until the ice is delivered by a specialised company. A suitable recovery cylinder must also be obtained.

Method 2: “Recovery only unit (ROU)”


A second option for extracting coolant blends safely and efficiently has recently become available: MAHLE, in cooperation with a number of automobile manufacturers, has developed a purpose-built device: the recovery only unit (ROU). Thanks to the ROU, it is now possible to recover gas mixtures much more easily and safely than with the dry ice method—in around 40 minutes, with virtually no residue!

The benefits of the ROU

  • Safe operation: risk-free, reliable, efficient recovery
  • Easy handling: lightweight, compact, transportable unit
  • Faster service: no additional media required
  • Unique technology: already patent-pending!

How exactly does the ROU work?

The ROU is a compact unit used to recover refrigerant in a separate, closed circuit. It uses no electric components and is operated in conjunction with the existing A/C service unit.

MAHLE A/C service units for R1234yf

That’s how easy it is to do the extraction:

  • Connect the high- and low-pressure hoses from the A/C service unit to the corresponding ports on the ROU using the service fittings.
  • Then connect the high- and low-pressure hoses from the ROU to the vehicle’s HVAC system.
  • You can now switch on the A/C service unit and start the special ROU cycle: the refrigerant flows through the expansion valve into the integrated heat exchanger and begins to evaporate. As the refrigerant expands, the temperature in the heat exchanger drops to approximately -30°C, and the extraction process begins.
  • The refrigerant from the vehicle flows into the integrated tank in the ROU. The process takes approximately 40 minutes (30 minutes cooling, 10 minutes heating), but over 92 per cent of the unidentified refrigerant is extracted during the first few minutes. The pressure in the refrigerant circuit can be monitored with the built-in gauge.
  • The unidentified liquid refrigerant can then be transferred from the ROU into an evacuated recovery cylinder via the drain valve. A sight glass can be used to carry out the transfer.
  • The entire process takes place automatically with instructions from the A/C service unit software.
  • You can now properly dispose of the contaminated refrigerant.


We regularly provide technical tips relating to the powertrain, thermal management, and mechatronics in automobiles.


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