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.
Replacing R600a with R134a is very poor practice. This also means that when removing the R134a for repairs you should recover the R134a from the system, something which I am reasonably sure does not happen.
R600a has been used to replace R134a because R134a is an HFC. HFCs are currently being phased down. Why? R134a has a high potential with regards to global warming and releasing R134a into the atmosphere is detrimental to the environment. In contrast, R600a has a very low impact on global warming. Fridge manufacturers are producing environmentally safe units running on R600a, but all the good work is being destroyed when a technician replaces R600a with R134a.
South Africa signed the Montreal Protocol which primarily addressed the ozone depletion issue. The subsequent amendments, in particular the Kigali Amendment (featured elsewhere in this issue) deals with global warming substances. This means that as a country we are committed to the phasing down of global warming substances such as R134a.
Margaret, it is true that there exists an additional safety issue when working with hydrocarbons (HCs). They are flammable, but with basic knowledge and easy to follow processes and precautions this risk can be reduced to low levels. There will always be some risk, but this also applies to R134a and in fact all refrigerants. Therefore, you should conduct a risk assessment before you start work to assess the possible risks and to take the necessary action to make the workplace safe.
Margaret, let us begin with what is R600a?
R600a is an HC and as such is flammable. R290 is also an HC and should you run into a light commercial fridge or beverage cooler you will, in most newer models, find that the unit utilises R290. The same safety rules apply. R600a is pure iso-butane and has a boiling point of -12°C at atmospheric pressure; R600a is used in most, if not all new domestic refrigerators in South Africa.
All refrigerants must be extremely pure. They must have extremely low levels of moisture and other contaminants.
The use of impure HCs will cause the following problems:
- High levels of moisture may saturate the filter drier, freeze in the capillary tube and can lead to compressor damage and failure.
- HC refrigerant manufacturers do not add a stenching agent and thus concentrations of HC refrigerant cannot be smelled.
- HCs when used as a fuel are not the correct composition for a refrigerant. It will not give the correct refrigeration capacity, and its use may result in higher running costs and poor reliability.
Therefore, only use refrigerant grade R600a.
HCs are flammable when mixed with air and ignited. The concentration of HC in the air must be between the lower and upper flammable levels as shown below.
- If the concentration is below the lower flammability level (LFL) of approximately 1.8%, there is not enough HC for combustion.
- If the concentration is above the upper flammability level (UFL) of approximately 8.9% there is insufficient oxygen for combustion.
- The LFL is approximately equal to 35 g/m3 of HC refrigerant in air. For safety reasons a practical limit of 8 g/m3 of HC in air should not be exceeded in a closed space.
Consider the fire triangle – oxygen, fuel and an ignition source – all three have to be present for fire to be maintained. Remove any one of the three and combustion is not possible. For combustion there must be an ignition source. The ignition source must be hotter than 460°C to ignite the R600a refrigerant.
The following represent potential ignition sources:
- Static electricity
- A flame, such as from a brazing torch, halide torch, match or cigarette lighter
- A spark from an electrical component such as a switch, thermostat, starting relay, overload protector or loose wiring connection
We need to realise that combustion will not occur inside the system as there will not be enough oxygen present. Even if a system is not evacuated before charging, there will not be enough oxygen for combustion. Combustion can occur if a leak of HC results in a flammable mixture and there is an ignition source.
Refrigerant R600a leakage can be dangerous if:
- Refrigerant leaks into a closed cabinet (or other sealed space) and there are electrical components inside the cabinet. Consider those custom kitchens with the fridges built in
- Refrigerant leaks into the air around the system and there are sparking electrical components on the system
- Refrigerant is lost during servicing (for example, when venting, flushing or charging a system), and there are sparking electrical switches and / or flames
Margaret, the flammability aspect requires some simple workplace precautions:
- Work in a well-ventilated area, or outside
- No smoking
- Demarcate the area using applicable signs
- No flames within 2m of the charging / venting area
- Do not use switches or any ignition source within 2m of the charging / venting area
- Use tools and equipment designed for use with HCs
- Have a fire extinguisher (dry powder type) on hand
- Use your personal protection equipment (PPE)
- Remember that HCs can accumulate in chest cabinets and basements
Handling R600a cylinders
Cylinders containing HC refrigerants should be clearly labelled to show the type of refrigerant and that it is flammable. This label should not be removed.
The guidelines below are similar to the guidelines for any refrigerant cylinder:
- Do not store HCs indoors
- The valve cap should be fitted when the cylinder is not being used
- If a cylinder needs to be heated it should be placed in a container of water no hotter than 45 to 50°C
- The cylinder and its valve should not be modified
- The cylinder should not be re-filled unless it is designed for recovered refrigerant
Design of HC appliances
HC appliances usually have electrical components that are either:
- Solid state
- Enclosed in a sealed box
- Located remotely from the refrigeration circuit
This avoids the risk of combustion if HC refrigerant leaks from the circuit. When replacing these components you must use the same type and fit them in the same position. If you need to open a sealed enclosure, make sure you re-seal it correctly.
Servicing procedures with HC refrigerants
Servicing procedures for HC refrigerants are similar to those for R134a, except for the additional precautions needed for working with flammable refrigerants.
We will look at:
- Safe venting of HC refrigerants from systems
- Removal of remaining HC refrigerant
- Replacing system components
- Pressure testing
- Leak testing
- Sealing the process tube
- Leak testing of process tube
- Remember that an HC and air are flammable and can be ignited by any ignition source.
- The HC refrigerant should be vented to an area away from ignition sources such as flames and sparks, preferably outside.
- The best tools to open the system are piercing pliers or a piercing valve, with a long hose connected and vented outside.
- Run the compressor, piercing pliers or a valve are not necessary if the process tube already has a connection on it.
- When pliers or a valve are used, make sure they are properly adjusted for the tube size, and make sure that if a rubber seal is needed, it is correctly located and is in good condition.
- To vent the HC safely, follow the procedure outlined below:
- Run the compressor, if possible, before venting refrigerant – this heats up the compressor oil so that less refrigerant will be dissolved in it.
- Do not open the system in an enclosed area – work in a well-ventilated area with windows and doors open and/or fan running, or outside and not underground.
- The vented refrigerant must not be drawn into a building or underground area. R600a is heavier than air.
- Before you use the piercing pliers or valve to open the system, put the other end of the hose outside or in a well-ventilated area. The area where you are releasing the refrigerant must not have any ignition sources such as flames and sparking electrical components.
- Pierce the process tube: take care to ensure that the pliers or valve are adjusted so they clamp firmly onto the process tube and that refrigerant does not leak from this connection.
- It can take up to 15 minutes for the refrigerant to be vented from an appliance in this way. Check that no more of the refrigerant is coming out of the hose before proceeding further, for example by putting the end of the hose in a container of water and looking for bubbles. Most of the refrigerant will be vented by this procedure, but some will remain in the oil and the system.
- Connect a vacuum pump and draw vacuum on system. The remainder of the refrigerant will be removed by the vacuum pump. Use a service line on the pump outlet to vent outdoors if needed.
- Your vacuum pump probably has an on/off switch which can spark when used. Do not use this switch when you use the pump to evacuate an HC system. Switch it on and off at the mains.
- You may assume at this point that all the HC refrigerant has been removed from the system. But if a blockage has occurred in the beginning of the capillary tube the entire high side of the system will contain HC refrigerant.
- Should you feel that the system has no HC refrigerant you may decide to remove the drier using an oxy acetylene flame. Stop!! Before doing so consider: If the capillary tube is blocked would you expect to find refrigerant in the pencil drier? Well, in reality the drier will be full of liquid HC refrigerant.
- Should you at this point try to remove the drier by heating up the drier with a flame the pressure inside the drier will rapidly increase and the drier will explode, spraying desiccant, copper pieces and highly flammable burning HC refrigerant close to your face. Yes, this is very dangerous.
- Rather first pierce or cut a hole in the drier. Trapped refrigerant will be released and as you are in a ventilated area the refrigerant will disperse, causing no damage or injuries.
- The piercing pliers or valve do not usually give a good enough seal for evacuation and charging, so they are removed at this point.
- If the process tube is not long enough to fit a valve, you will need to braze on an extension tube – remember to have drawn a vacuum to remove refrigerant absorbed in the oil. You can make a flare at the end of the process tube and connect a valve to it.
Replacing system components
You must use the correct electrical components if you need to replace these items, and you must replace them in the correct way.
In most HC appliances:
- The compressor relay is solid-state and the overload protector is a sealed device, to prevent sparking.
- The thermostat is either located in a sealed electrical box or a solid state/sealed type is used, to prevent sparking.
- On/off and door switches are sealed types, although usually they are not fitted.
- Standard capacitors and induction type fan motors are safe to use with HCs as they do not spark.
If you need to replace a sealed or solid-state device, use the correct safe type. If you need to replace devices which are mounted inside a sealed enclosure, make sure you put them again inside the electrical box and seal it properly, including the cable entries. Make sure any wiring connections cannot work loose – loose wires can cause sparks.
Margaret, in the next issue I will continue with pressure testing, leak testing evacuation and charging R600a systems.
Thank you for the question, Margaret. Let us understand hydrocarbons, they are the future.
Thanks to everybody for the overwhelming response.
Looking forward to hearing from you.
- The Fridge Factory
- merSETA training
- USFDA / FEMCO
About 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.