KEEPING COOL: AIR CONDITIONING

Transcription

1 TECH NOTE KEEPING COOL: AIR CONDITIONING Words: Dougie Photos: Steve McCann As the weather gets warmer, we take an in-depth look at all the gas and gubbins that keeps you feeling cool when you re out cruising the streets. A working air conditioning system is a nice thing to have. Not so long ago, air con was almost exclusively the preserve of high-end luxury cars in this country, but in the last ten years or so it s become almost standard across the ranges of most manufacturers. The problem with it, though, is that most owners are unaware of what exactly it does (yes, we know it blows cold air out on hot days) and how it should be maintained. A result of this is that many cars now have systems that operate poorly, or even worse, not at all. If systems are left in a state of disrepair, it can mean failure of components such as the condenser and compressor and you don t want this, because it means big bills. On older cars, it can sometimes become financially impractical to get the climate system fixed, which isn t good as a car with a fully working air con system will always be worth more when you come to sell it, not to mention it making your car a much nicer place to spend the summer months. In short, it s best to keep air con in fine working order. The good thing, though, is that keeping your air con system in good condition and even getting it repaired need not break the bank. You can buy a tin of air con gas over the internet and try and re-gas your car on the cheap, but really it s a false economy because it can be hard to gauge exactly how much gas is in the system to start with. So, it s better to get an expert to take a look at it for you. Air conditioning systems require specialist knowledge and equipment, so we ve enlisted the services of Brian Sibbald of automotive air con experts, Freez Breez. The company uses state-of-the-art equipment to repair and re-gas just about anything you can think of that has wheels and air con. According to Brian, simple annual maintenance procedures should mean that you avoid any major problems, so let s have a look at what this entails. We ve taken the Cavalier GSi 2000, which was fitted with air con as an optional extra at the factory, and passed it onto Brian to have the system checked and re-gassed. Over the next few pages, we ll take you through the procedure step by step. Because the car was registered before 1993, the system contained old CFC R12 gas, which is no longer used for environmental reasons. We had the car converted to the new R134a gas in accordance with all regulations currently in force check the boxout on the next page for more info. C t t v 118 TOTAL VAUXHALL TOV59.tech /5/06 8:39:25 pm

2 HARDCORE REFRIGERANT GASSES As mentioned, there are two kinds of air con gas. The first is R12, which was used up until This gas is a CFC (chlorofluorocarbon) refrigerant and was outlawed as a result of the Montreal Protocol a study into reports of depletion of the ozone layer. Cars that have air con still operating on R12 gas are legal, but since October 1, 2000 it has been illegal to charge a system with the gas and it has no longer been available since that date. The main advantage of using R12 gas was that it could mix well with inexpensive mineral oil. The disadvantage of R12, apart from its ozone-depleting qualities, is that when it s heated to a high temperature with a flame present, the resultant chemical reaction produces phosgene which is a nerve gas. Ouch. The second gas is R134a, which was developed to comply with the Montreal Protocol. This gas is a HFC (hydrofluorocarbon). It s been used in car air con systems since about 1992, but like R12, it also produces a deadly gas if burnt. R134a will not mix with mineral oil like R12, so synthetic oil must be used. This oil, which is called PAG (polyalkalene glycol), has three different grades: ISO46, ISO100 and ISO150. Your car s compressor will determine which grade is necessary. There are also universal oils available, which we re using here. One problem with R134a is that its molecular structure is very small in comparison to that of R12. This means that any leak on a system, no matter how small, can result in refrigerant loss in a very short period of time. This also presents a problem for R12 systems that have been retro-gassed with R134a, because the old-style pipes and tubing on the system will not be fitted with a nylon-lined barrier hose. On an old car, it s likely that replacing the hoses will not be cost-effective (probably over 500) and it d be cheaper just to get it re-gassed annually. AIR CON DIAGRAM Here s the kit that keeps you cool. COMPRESSOR The refrigerant in the system is present in two forms. The purpose of the compressor, which is driven from a belt from the engine, is to convert the refrigerant gas from an LP vapour (suction) to an HP vapour (discharge). Once the process is complete, the vapour is passed to the condenser. CONDENSER The condenser is the second radiator at the front of the car, and you ll find it sitting behind the bumper. The HP vapour is passed into the condenser, where it is converted into HP liquid. The condenser is fitted with a fan which will engage should the system start to overheat. The HP liquid is then sent out of the condenser and passed into the orifice tube. ORIFICE TUBE This component drops the pressure and temperature of the HP liquid so it can be passed to the evaporator as LP liquid. EVAPORATOR The evaporator is a set of tubes under the dashboard that is made icy-cold by the LP liquid. The outside air is passed over these tubes, making it cold in the process, and then piped into the car interior. Inside the evaporator, the liquid starts to turn back into LP vapour but still contains fluid, which leads us to the final step in the cycle. ACCUMULATOR Any leftover liquid from the evaporator is converted back into LP vapour here, before it s passed back into the compressor ready to be pumped round the system again. SAFETY FEATURES Pressure switches protect the entire system. There are two problems that can cause component failure, namely a loss of refrigerant or a blockage in the system. If either of these two faults occurs, the compressor must be stopped. In the case of the GSi, the system had no refrigerant left and the lowpressure switch detected this, so the power to the compressor was cut and the air con button on the dash was deactivated. Had there been a blockage, the highpressure switch would have done the same thing. LP vapour and liquid Accumulator HP vapour Compressor Cool Air to cabin through vents Internal fan LP vapour Condenser External Ram Air Evaporator LP Liquid Orifice tube HP Liquid HP = High Pressure LP = Low Pressure TOTAL VAUXHALL 119 TOV59.tech /5/06 8:39:37 pm

3 TECH NOTE HOW TO RE-GAS AN AIR CON SYSTEM 1 As mentioned previously, R12 gas is banned. So, the gas existing in the system must be recovered by connecting a suction machine to the HP and LP ports on the accumulator. 2 The suction machine removes the gas from the system and transfers it into the grey bottle, which sits on a charging scale. R12 must be recovered into a separate bottle to R134a, because they do not mix. The scale ensures that a bottle cannot be overfilled with gas. 3 The next step is to check that the system is capable of accepting a charge without leaking. To do this, oxygen-free nitrogen is used. If oxygen becomes present in the system, it will mix with existing gas and oil and start to eat away at the pipes. The OFN is pumped into the system via the accumulator to a pressure of 120 psi, which is displayed on the gauges. The system is left for some time while the pressure is monitored. The compressor is then checked to see if it operates properly by switching on the air con very briefly via the switch on the dash. 4 The gauges are checked and it s clear that the system has held pressure way in excess of what it actually needs to operate. OFN is harmless and can now be vented to atmosphere. 5 The service adaptors on the accumulator must be changed to the new R134a type before we can proceed any further. Note the different sizes of the new adaptor on the left. 120 TOTAL VAUXHALL TOV59.tech Sec3:120 25/5/06 8:39:43 pm

4 HARDCORE 6 The system is then connected to the Bosch ESI Tronic Mobile Air Con Recovery And Recharge machine to start the process of re-gassing. First, a deep-vane vacuum is created that breaks up any leftover moisture in the pipes and removes it. In the summer this can be done fairly quickly, but as it was freezing cold when we were working on the car, it was left to vacuum for 15 minutes. When complete, the screen on the machine displays a vacuum of 940 millibars. Anything less than 870 millibars means that the system is losing vacuum and will not allow gas to be put in. 7 The next phase is to add the oil to the system. There is a bottle attached to the side of the machine that sucks the oil in, ready for it to be entered into the accumulator. 8 Retrofit Pro gas is added via the LP port to allow the R134a to mix with any residual mineral oil. The can is screwed into the adaptor, which pierces the lid and causes the gas to be sent in. THANKS RCA Garage Services and MOT Centre Stoneyburn West Lothian TOTAL VAUXHALL 121 TOV59.tech Sec3:121 25/5/06 8:39:49 pm

5 TECH NOTE 9 The LP side is then reconnected, and we find that the system requires a certain amount of gas to be inserted. Autodata states that 800g of gas must be entered. This information is punched into the machine and the gas is then pumped in. Once this is done, the taps are shut to prevent the compressor on the from car firing the gas back into the machine. 10 All that remains now is to start the car and check that everything works. The dash switch now illuminates because the pressure switches have detected the correct pressure in the system. After a minute or so, cold air is blowing through the vents and the system is operating nicely. 122 TOTAL VAUXHALL TOV59.tech Sec2:122 25/5/06 8:39:54 pm

6 HARDCORE One of the advantages of R134a gas is that it is treated with a UV dye, which means leaks can be detected with a UV light. We checked out the condenser with the light just in case anything showed up. Finally, the scuttle panel is stickered-up with the relevant information about what we ve done, so there s a clear reference point for anyone carrying out work on the air con system in the future. QUICK AIR CON FAQs How do I test the air con system on a car that I m about to buy? Set the temperature to Cold, switch the air con on and the fan to stage II. The air should become noticeably cold within a couple of minutes and stay that way. If it doesn t get cold, there s a problem. This could mean it just needs a simple re-gas, but it could also signify a new compressor and condenser, which can mean huge four-figure bills if you re unlucky. Why do I need my air con serviced? All vehicle air con systems leak to some degree. Refrigerant is lost through pipe joints, rubber hoses, O-ring seals and the seal on the front of the compressor shaft. Vibration and old age also take their toll on the components. Systems should be serviced once a year. Is it a good idea to run the air con regularly, even in winter? Yes. This helps keep the system well lubricated and free from leaks. Why is looking after the compressor component so important? This is the main unit of the air con system and replacements typically cost plus labour. A seized compressor can also cause damage to other components. Why can t I service the system myself? Specialist equipment is required, but most importantly the refrigerant in the system must be recovered. It is illegal to vent it to the environment. The system is also under a high pressure and needs pulling into a deep vacuum to remove any moisture. In addition, the refrigerants have a very low boiling point and can cause freeze burns. How much does it cost for a service? Freez Breez will re-gas systems for 50 upwards. A conversion from R12 to R134a (as seen here) will cost about 170. For an example of repairs, a common fault on the Vectra B is the pipe at the manifold that comes off the compressor. This can split, normally behind the heatshield. The pipe costs about 80 on its own and about 180 to have it supplied, fitted and re-gassed. An OEM condenser for a typical Vauxhall costs about 150, including VAT. Supply, fit and re-gas costs around 250. CONTACTS Freez Breez engineers are certified to City And Guilds 6048 in Motor Vehicle Air Conditioning and CITB-qualified in Refrigerant Handling. Freez Breez Vehicle Air Conditioning Services 45 Harvie Gardens Armadale West Lothian EH55 8BP TOTAL VAUXHALL 123 TOV59.tech Sec2:123 25/5/06 8:40:00 pm