By Grant Laidlaw

Many people ask for assistance in the understanding of theoretical and practical aspects of the industry. I will endeavour to enlighten. I am going back to basics as I have questions coming in which indicate that the basic understanding necessary to work in industry is not in place.

Margaret asks: I am an apprentice, and our company does fridge repair. Could you please explain the service and repair issues when working with hydrocarbon R600a. I have seen people taking out R600a and simply replacing it with R134a where I work, they say it is safer.

Hi Margaret, I would imagine that you work in the smaller capacity domestic refrigeration market where you are running into R600a. Continuing from last month’s feature, we will now look at service procedures beginning with pressure testing.

Servicing procedures with hydrocarbon refrigerants

Servicing procedures for hydrocarbon (HC) refrigerants are similar to those for R134a, except for the additional precautions needed for working with flammable refrigerants.

We will look at:

  • Pressure testing
  • Leak testing
  • Evacuation
  • Charging
  • Sealing the process tube
  • Leak testing of process tube

Service Practice

Remember that HC refrigerants (R600a) are flammable and can be ignited by any ignition source. It is best to work in a well-ventilated area or, if possible, outdoors. When venting, an HC refrigerant should be vented to an area away from ignition sources (flames and sparks), preferably outside. The best tools to open a system that does not have service valves is by using piercing pliers or a piercing valve, with a long hose connected and vented outside.

  • 1: Pressure testing

The HC system can be pressure tested in a similar way to R134a systems. It is preferable to use dry, oxygen free nitrogen for pressure testing. Note – dry, oxygen free nitrogen is 99.997% nitrogen. Testing pressure should be 1.3 times the working pressure, as used previously.


NB: You must use a pressure regulator when working with nitrogen, we see many accidents and even deaths resulting from technical people working with nitrogen cylinders without a regulator.


  • 2: Leak Testing

The refrigeration system must be tested for leaks when fault finding and before charging the system. The safest and most accurate method for leak testing is with an electronic leak tester but one can use soapy water while the system is still pressurised with dry nitrogen.

On a system charged with refrigerant each joint should be checked with the system at the highest practical pressure. What do we mean? The low side of the system should be leak tested when the system is not running; and the high side should be tested when the system is running as this gives the highest pressures in the system under these conditions and gives the best results for leak testing.

  • 3: Evacuation

The system must be evacuated to remove moisture and non-condensable gases such as air. If a system is not evacuated properly the system will not give required performance. With HC refrigerants there is no need to evacuate the system for any longer than you would do for R134a. A system should be evacuated to 500 microns. Again, when you evacuate the system, work in a well-ventilated area or outside. Connect a line to the outlet of the vacuum pump and vent to a safe ventilated area. Use the wall socket switch and not the switch on the vacuum pump to turn your vacuum pump on and off.

  • 4: Charging

Refrigerant should only be charged into a clean, dry, leak free system. You must evacuate the system before charging with refrigerant. When charging HC refrigerant you must not do any work with hydrocarbon refrigerants in confined spaces.

Make sure that:

  • the charging area is very well-ventilated (or outside)
  • the charging equipment is suitable for use with HC refrigerants, that it is safe and accurate
  • you vent as little refrigerant as possible into the air
  • you have a dry powder type fire extinguisher in the charging area
NB: you can take charge from the cylinder in the liquid or gas state. (Not applicable to blends).

The area where you charge refrigerant into an appliance should be very well ventilated or outside. To be safe the charging area must:

  • be a no-smoking area
  • be at least 2m from flames and sparking electrical components
  • never be below ground

Do not store refrigerant in your charging area, hydrocarbons should be stored outside (i.e. as LPG is stored), under cover as previously described.

Charging equipment: There are different methods of measuring the amount of refrigerant charged into a system:

  • By weight, using an accurate digital scale
  • To known suction and/or discharge pressures
  • To a frost line: this is not very accurate and should be used only for small, fixed orifice systems running at the required temperature

The amount of refrigerant charged into a system affects its performance. If too much or too little refrigerant is charged, the capacity of the system will be lower than expected and/or the power consumption may be higher.

Weighing the refrigerant is the most accurate method and should be used for all refrigerants where possible. Use an electronic scale with an accuracy of ±1g when charging systems with less than 100g of refrigerant. For greater charge weights less accuracy is acceptable. Electronic scales are safe to use with HC refrigerants, you do not need to make any changes. The amount of refrigerant that one should charge into a system is found on the system’s data plate. If you do not know the weight of refrigerant, then charging to the correct suction pressure is the next best method.

Whichever method is used, make sure that if your charging equipment is also used with another refrigerant, for example R134a, you do not contaminate the HC refrigerant.  Evacuate or purge equipment such as hoses before using it on a different refrigerant.

Charging to the correct suction pressure: Appliances are often charged with refrigerant while they are running, and the refrigerant is slowly charged in until the correct suction pressure has been reached. This method is not as accurate as charging by weight. Test work has shown that the error in refrigerant amount is ±15%. This can significantly reduce the capacity and efficiency of the appliance.

The equipment used for this procedure usually consists of suitable hoses and a gauge manifold. Typically, the suction pressure for R600a will be close to atmospheric pressure for a chilled food appliance and will be lower than atmospheric pressure for a frozen food appliance.

Summing up the procedure for charging HC refrigerants:

  • The procedure must be followed for safe and accurate charging.
  • The steps are good refrigeration practice.
  • All of your tools, instruments and equipment must be suitable for use with HC refrigerants.

 Ensure the area is ventilated or work outside: This will ensure that any HC refrigerant which leaks will be safely dispersed. There must be no flames or ignition sources within two to three metres of the charging area. Switches within two to three meters of the charging area should not be used. A dry powder type fire extinguisher must be present in the charging area.

Connecting the charging hose(s) and manifold sets: The hoses should be as short as possible to reduce the amount of refrigerant vented; for example, if there is a problem during charging shorter hoses mean less refrigerant being vented. Connect the hose(s) to the charging equipment and system. If there is air in the hoses (or any other gas that is not HC) you must remove it. Avoid purging the hoses if possible. If you can, you should evacuate them using your vacuum pump. If you do purge the hoses, do this carefully using refrigerant from the cylinder. Purging is more hazardous when flammable refrigerant is used, so minimise the loss of refrigerant by venting off the air at the connection to the system by purging for one second. This is sufficient time to push air out of the lines.

Charging the HC refrigerant: Accurately weigh in the HC refrigerant. Refrigerant is charged into the process tube of the compressor so any liquid must be evaporated before it enters the compressor. Once charging is complete remove the charging hose(s) carefully to minimise the amount of refrigerant lost. Do this by closing the cylinder valve and running the system to draw in as much refrigerant as possible from the charging hoses, closing the manifold gauges and sealing the process tube. Do not remove the label (showing refrigerant type) from the cabinet. If it has already been removed or is difficult to read, replace it.

  • 5: Sealing the process tube

To remove the necessity of brazing on the process you can leave the shroeder valve fitted to the system prior to charging but one can braze the process tube closed. The charging connection can be brazed, but care must be taken. It is not possible to ignite the HC refrigerant in the system because it has no air mixed with it. Ventilate the area before you light your brazing torch and while you braze. This will ensure any HC refrigerant that has leaked into the air has been safely dispersed.

To seal the process tube by brazing:

  • Pinch the process tube using pinching pliers or a pinch off tool
  • Leave the pinching pliers or tool in place and use an electronic leak detector or soapy water to check for leaks at the end of the tube
  • Braze the connection
  • Remove the pinching pliers or tool and test for leaks again. Strengthen the area where the pipe has been pinched to prevent bending and later possible leakage at this point
  • Check the process tube for leaks as described
  • 6: Leak testing of process tube

When the system has been charged and sealed, the process tube and the entire system should be checked for leaks as described above. Do not check the low side of an R600a system while it is running, the pressures are too low for accurate testing. If a leak is found the refrigerant should be safely removed and the system evacuated as described earlier before the leak is repaired.

Margaret, thank you for your question on HC domestic systems utilising R600a. Remember that only SAQCC gas authorised refrigeration practitioners may work with refrigerants. Let us understand hydrocarbons, they are the future.

Thanks to everybody for the overwhelming response.

Looking forward to hearing from you.

Grant Laidlaw


  2. The Fridge Factory
  3. merSETA training

About Grant Laidlaw

Grant Laidlaw

Grant Laidlaw is currently the owner of the Air Conditioning and Refrigeration Academy (ACRA) in Edenvale. He holds a Bachelor of Business Administration and an associate degree in educational administration. He has a National Technical Diploma and completed an apprenticeship with Transnet. He has dual-trades status: refrigeration and electrical. He has been involved with SAIRAC for over two decades and served on the Johannesburg committee as chairman and was also president between 2015 and 2018. Currently he is the SAIRAC national treasurer.

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