Frequently asked questions

Q. How does my A/C work? – If you are the inquisitive sort this explanation might be right up your street.

Figure 1

A. There are five main parts to the Air conditioning system on most cars and they are:

• · The Compressor
• · Condenser
• · Evaporator
• · Receiver Drier
• · Expansion valve.

The engine drives the compressor, which sucks the refrigerant gas through the pipe from the evaporator and compresses it to a high pressure. The evaporator also known as the heat exchanger is located next to the heater matrix in the centre of the dashboard inside the Air Distribution Unit.

As any Physics student can tell you; Compressed gas heats up considerably and this is where the condenser fits in (that’s the large radiator in front of the cooling radiator) the gas, typically compressed to 250psi, enters the top of the condenser where it is cooled and like cooled steam turns to water (condensation) the gas in the condenser turns to liquid refrigerant and passes on its way to the Receiver drier which removes any moisture through the use of desiccants and also filters out any contaminates..

With every thing still under high-pressure this side of the compressor (High side) the liquid refrigerant moves to the expansion valve which has a small opening in it into the evaporator. Through this small opening the liquid refrigerant is metered and squirted into the evaporator where it meets a low pressure. As the liquid now has room to expand in this low-pressure area (something it will want to do) it turns back to gas. The energy created in turning the liquid to gas will absorb heat. Hence the evaporator starts to remove the heat from the inside of the car – thus making it feel cooler. Many people are under the impression that the Air con is blowing cold air but the truth is it is using up the warm air it needs to metamorphosis back to gas and the result is a cooler interior. Then the cycle starts again as the compressor is sucking the gas in the evaporator, which is, where we started.

Some of the most overlooked benefits from this process are that not only does your cars interior feel cooler but the A/C is also drying the air and most pollutants are captured in the water formed by the air travelling through the evaporator as it does its thing That is why it is important to make sure the two drain tubes are clear in the bottom of the distribution unit.

Apart from the system needing to have the correct amount of oil (Mineral based in R-12 and ether Glycol or Ester based in R-134a) and refrigerant, it must also be leak free. One of the most overlooked faults though is a blocked Condenser. By blocked we are talking about an air flow restriction caused by faulty fan couplings or electric fan failure together with blocked fins (often accompanied by an over heating engine) For those interested in Jaguar XJS and XJ6/12 Delanair Air con distribution units we have detailed the differences on a separate page. and further information is available on our sister site skjagtech.co.uk

Q. What about fuel consumption?

A. Well yes it is true that your AC will increase fuel consumption but it largely depends on how you drive. If you are popping to the local shops, your AC will be on all the time trying to get the interior cool. Just as it achieves it you park up for an hour or so and the car heats up again in the sun, now when you return and come home it’s working hard again resulting in more fuel being used. On the other hand if you are winging it up the motorway or going for a run around the countryside for half an hour then the cost is negligible, as once reached, the cool temperature just needs to be maintained. Some are of the mind that it would be cheaper just to open the windows. They are wrong. This considerably disturbs the aerodynamics of the car that the manufacturer went to such lengths and expense to improve, thus increasing the fuel consumption.

Q. I've heard that AC is the cause of global warming

A. This is not strictly true. There are many pollutants that have caused depletion of the stratosphere and AC, although one of them is only a culprit through miss-use. In the early days there was no knowledge of the harms that CFCs did, and unlike today, where the refrigerant is recovered and recycled using specialist equipment, AC’s were just recovered to the atmosphere as some manuals of the time suggest. No one is to blame, as no one knew how damaging these gases (CFCs) were.

The term “mis-use” applies to incorrect maintenance and routine checking. You should find yourself a good AC shop and get them to regularly check your system especially if you are finding the system is not cooling like it used to.

The home mechanic can help himself or herself out by having an Ultra Violet (UV) additive put in on the next recharge. You can then purchase a UV light, which are available all over the place these days for a few £/$/E, and use it to check over the pipes and fittings. At this point if you spot the dye leaking out don’t use the system until you have the shop repair it.

If you suspect or find a fault, we would strongly recommend that you disconnect the compressor clutch ether by removing the drive belt or simply unplugging the electrical connector on the compressor. Older Harrison (actually a GM A-6) compressors have a sensor that fries a fuse on the compressor mounting plate and does this by using a probe in the rear of the compressor body, which detects the excess heat; now these fuses aren’t cheap, so better to disconnect that compressor before the system does it for you. Later types had pressure sensors and did not require the fuse as they just interrupted the electrical flow. Most others have an electrical plug that can simply be disconnected and taped over to prevent short circuits

Q. What refrigerant should I use?

A. Since around 1995 R-12 production has been banned in EU countries. R-12 (dichlorodifluoromethane) was the refrigerant used in most vehicles built before 1993 and is a CFC (chlorofluorocarbon). It was the most popular choice of refrigerant for decades; developed in 1928 it was widely used in a number of appliances that needed cooling. In 1974 research by Prof. Sherwood Rowland and Dr Mario Molina from the Dept of Chemistry, University of California at Irvine first theorised that CFCs were causing damage to the Ozone layer. No one had realised until this research that these CFCs were harmful to the environment and that’s when alternatives were sort after. Enter R-22 (chlorodifluoromethane). R-22 is a HCFC (hydrochlorofluorocarbon) and the Hydrogen molecules help it to decompose in the atmosphere because HCFC’s are less stable than CFCs (which being stable converts O³ to O² (Ozone to Oxygen)). This was still not perfect as HCFC still has the harmful Chlorine content the same as CFCs. Today we mostly use a safe refrigerant known as R-134a (1,1,1,2-tetrafluoroethane) and most AC shops recommend that you have your R-12 system retrofitted to R-134a, which is a HFC (hydro fluorocarbon) refrigerant. Retro fitting is a little complicated, it requires ideally a larger condenser due to R-134a operating at a higher pressure than R-12 thus requiring a larger cooling area and You will also need different high and low side service ports (R-12 are screw on, R-134a are quick connect (which also helps stop cross contamination). It is recommended that you fit a new compressor (typically, around £200.00 to £400.00). These are often found to be a reason the system isn’t working or performing well as they dry out and the seals degrade. This is a common fault often introduced by the user not using the A/C throughout the year in a misguided attempt to save fuel and not realising the benefits of A/C even in the depths of winter. As always when ever the system is opened for servicing you should have a new Receiver Drier (RD) fitted, as the desiccants will be water logged after a time. Ideally you want to have it changed every 2-3 years. receiver driers are cheap (Yes that’s right you did read that correctly – Cheap) costing around £35.00 and when you consider that an oil filter or fuel filter can cost £10.00 each and you change them every year (you do change them every year don’t you?) the receiver driers is cheaper requiring replacement less often. It has come to our notice that there are a lot of USED receiver driers being offered for sale on internet auction sites - Avoid these they are probably passed there best by date and now that the seller has removed it from the car its odds on favourite they did NOT seal the ends with in 5 minuets of removing the pipe fitting. and desiccants, being what they are, absorb moisture in the air real quick. These used units are a waste of money.

Q. With all these high pressures and gases, could my A/C explode?

The short answer is, yes it can, but normally in the rare case that this happens it is due to a road traffic accident whilst the system was running. The rupture is instant and normally at the front of the car away from the passengers. A 250+psi rupture in the car is extremely if not impossibly, rare as the passenger compartment only has low-pressure refrigerant. Modern cotton wool legislation would have banned Air Con if there were a danger of it causing injury to the occupants of the car, remember the evaporator, the only component of the refrigeration system that is in the car, is a low-pressure component. Given the fact that the components would leak before completely braking apart the chances of an explosion in normal circumstances would be extremely minimal due to gradual failure of the systems ability to maintain pressure. The main danger from refrigerant is from inept technicians and there are reported cases of death due to asphyxiation, as refrigerant gases being heavier than air, have removed all the Oxygen from the work area, well what can we say they should have been trained better and had better working practices the fault surely lays firmly at the feet of their employers. There is no excuse for not knowing; any half intelligent, responsible adult knows that refrigerant is dangerous. Not to provide correct training/knowledge to those in your employ is criminal to say the least.

Q. I need to do some work on my car and need to remove a part of the AC system, what should I do?

Simple – Get your AC evacuated by a professional outfit first and disconnect the compressor if you need to drive the car. Most, including us, Air Con equipped workshops will come to you so there should be no need to drive the car. You MUST be a responsible human being and have the gas evacuated properly, letting that refrigerant (EVEN R-134A) into the atmosphere is just dame right irresponsible. This planet is the one your children and their grand children are hoping to inhabit. Never evacuate to the atmosphere it’s just not going to help things for them. We have been irresponsible, thus far, due mainly to lack of knowledge but now EVERYBODY knows about global warming and the death of the planet. Please DON’T add to that destruction. We know this sounds like we are tree huggers (not that we have anything against that practice we are sure its very rewarding for those that do and they should by all means carry on) but there is no excuse on this earth for evacuating to atmosphere. If you are local to us we can do this for you. The charges we would make are for the recycling of the gas, a small labour charge and relevant call out fee– moan over but seriously this is no joke.

Once evacuated it will be safe for you to remove whatever component(s) you need too. Please be aware that there will be oil in the system after evacuation and this needs to be carefully removed and saved, most but not all should come out of the Harrison compressor. Hand this quantity of oil to your AC technician when you have the system recharged so that she/he knows how much to add back in when performing the over haul and recharge.

Q. I have a question?

A. Drop us a line –. We will be glad to answer your questions and it may even appear here in order to help other owners. On the other hand, if we don’t know the answer, we will ask someone who does know for you. It is not worth speculating where air conditioning is concerned

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