Air Conditioning

We frequently get asked to "regas" an air conditioner when it stops working. Unfortunately its not quite that simple which is why I have decided to write this article.

 

The first air conditioner to find its way into a car was back in 1940 in a very crude form. By 1969 around half of all new cars sold had factory installed air conditioning. Since those first days of air conditioning the refrigerant used, known as R-12, CFC-12, or its brand name in the USA Freon, was found to be damaging the ozone layer (it's a chlorofluorocarbon). It was banned from being manufactured and an alternative, called R-134a or HFC-134a, was required for all cars manufactured after 1994. R134a although not an ozone depleting substance, it is a very potent greenhouse gas. Because of this the handling of R134a is heavily regulated in Australia by The Australian Refrigeration Council (ARC). In short to legally handle R134a the individual must hold a specific refrigerant handling licensed which can only be obtained after specific A/C training. Also for a business to buy and sell R134a a Refrigerant Trading Authorisation is required. Businesses and individuals are audited frequently and any breaches found attract hefty penalties.

 

Air conditioning has worked pretty much the same way for its entire existence: it cools and removes humidity from the air. The main components of an A/C system are the compressor, the condenser, the evaporator, either a TX valve or an orifice tube and a receiver drier, plus all the hoses and pipes that connect everything.

 

    Compressor - An engine run pump which moves and compresses the refrigerant to around 300-450psi. That’s around 12 X the pressure in your tyres, or 27 times the pressure in your cooling system when the engine is at operating temperature.

 

    Condenser - A part very similar to the radiator which sits in front of the radiator. Refrigerant is passed through the condenser where it is cooled and changes from a gas to a liquid.

 

    Evaporator - A part similar to a radiator except much smaller. The evaporator lives with in the dash of a vehicle where air is passed through to cool. Within the evaporator refrigerant changes from a liquid to a gas (it evaporates) which is what creates the cooling effect.

 

    TX Valve/Orifice Tube - The Thermal Expansion (TX) valve is a valve located in the stream of refrigerant close the the evaporator. Its job is to throttle the air-conditioning system. The orifice tube is a small capillary with a fixed opening which does the same job as the TX valve except it is fixed and not variable.

 

    Receiver Drier - The receiver drier has a couple of tasks. It is a place to store excess refrigerant. It filters the refrigerant. It also has a desiccant which removes moisture from the refrigerant.

 

    Other Bits and Pieces - Pressure switch which won’t allow the compressor to turn on below a pre-set pressure, it protects the compressor. Pressure relief valve, designed to release refrigerant into the atmosphere if pressures within the system get dangerously high. Oil, a very specific oil throughout the system for lubricating the moving parts, mainly the compressor. Refrigerant, "the gas" which is used not only to cool the occupants but also the compressor which would operate at melting temperatures otherwise. Refrigerant also moves the oil around the system.

 

The A/C system is a closed loop system where refrigerant gets pumped by the compressor, at extremely high pressure around the system, it absorbs heat from within the cabin as it changes from a liquid to a gas (It evaporates), from there it goes to the condenser where it passes its stored heat to the passing air while changing from a gas to a liquid (It condenses) ready to complete the cycle again. An A/C system will naturally lose small amounts of refrigerant each year, normally around 10-15% for the first year, then the loss will drop off for each subsequent year as the pressure in the system drops. You would expect to see noticeable drops in performance after the third year of service.

 

Around 70% of the complaints we get about inoperative A/C present with no refrigerant in the system, so straight away you can see a problem, if there is no refrigerant in the system then where has it all gone, and the obvious answer is a leak, and with the pressures involved it doesn’t have to be a big leak. So the first problem with that 70% that want a regas is it won’t last, the refrigerant will leak out from the same place it leaked out from originally. So it is a waste of money, and it is illegal for a licensed technician to knowingly recharge a leaking A/C system.

This is from the ARC website:

"...By law, if a leak exists, all faulty parts must be repaired or replaced before it is refilled with refrigerant..."

 

About 15% of the complaints we see present with a failed compressor. Now compressors are quite durable and long lasting in normal service and rarely fail. However they can be fragile if mistreated. Remember from above what job the refrigerant has, apart from keeping the occupants cool, it also needs to cool the compressor and deliver a constant stream of oil to the compressor, now a system that loses small amounts of refrigerant each year will slowly start to lose its cooling ability for the occupants, and the compressor, add to that lower amounts of oil being delivered and soon enough the compressor fails but that’s not the end of the story. A term common in the trade is "Black Death" (see this pic of an orifice tube blocked with black death), a condition where as the compressor is failing it spreads a gritty metallic paste (made up of broken down oil mixed with metal shavings from the compressor)  throughout the entire A/C system. When this happens the repair bill is usually above $1000 at best. The condenser, the evaporator, the TX valve or orifice tube and the receiver drier will usually need replacement. The hoses are usually flushed. Around 5% of the people with inoperative or poor performing air conditioners that we see are due to various faults within the system such as compressor clutch problems (which can be usually repaired without replacing the compressor), electrical problems, blockage within the system, fan and vent problems.

 

The remaining 10% are the lucky ones. They have a functioning A/C system which has just lost a bit too much refrigerant but the compressor hasn’t  yet failed. All is required is a simple A/C system service which in most cases costs less than $200.

So what is a service? A service consist of evacuating the refrigerant left in the system, replacing the receiver drier, fitting new service valves, adding oil and some UV dye to the system, then placing a the whole system under a total vacuum for around an hour, then recharging with the correct amount of R134a. We then do a thorough performance test checking all components of the A/C system and an electronic leak test. This service should be performed every two years so as not to allow the refrigerant to drop to a level where compressor damage can start to occur.

 

So if gas is all it needs then why not just top it up? Firstly because it is illegal, from the code of conduct linked above:

"A.4.1 The addition of refrigerant to an existing system charge to “top up”

must not be carried out."

The real reason is moisture. As an air conditioner slowly loses refrigerant, the oil within absorbs  and holds moisture. The receiver drier is able to remove this moisture initially but as it gets saturated it is no longer able to absorb any moisture. Eventually enough moisture builds up to the point where the internals start to corrode, then as more moisture builds up is begins to freeze with in the A/C and causing blockages.

 

Tips for operating your air conditioner:

 

  • Run the A/C for a minimum 5 mins a week - This prevents the seals in the compressor from drying up from a lack of oil. I use my A/C in the winter time to defog my windscreen, it’s much quicker than using the heater alone and I don’t have to remember to turn the A/C on each week.

  • If you notice a drop in A/C performance stop using it until you have it looked at because the compressor is probably also not getting enough cooling refrigerant and get be damaged very quickly. I have seen a compressor fail in a little as two weeks after the condenser fan stopped working.

  • Use the recirculate function. It will help to keep the cabin cooler and place less load on the A/C. But remember  to switch over to fresh air every now and then to avoid it getting to stuffy.

 

A note on alternative refrigerants:

There are a handful of alternatives to R134a on the market today. These exist due to the high price of R134a and the licensing requirements associated with R134a. These refrigerants have different cooling properties to R134a and have been found to inefficient when it comes to moving oil around the system, and for this reason many new car warranties and compressor manufacturers will not warrant their product unless it used with R134a so use only a licenced establishment to service your cars A/C system. You can find who is licenced on the ARC website. Our authorisation number is AU27624.

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