About Your Car Air Conditioner
by Jamie Ruf
AUTO AIR CONDITIONING SYSTEM
Car air conditioning, which was once a great luxury, is now a common feature on most motor vehicles. While the servicing of modern car air conditioning systems is best left to professionals, you can get the most enjoyment from you’re A/C system if you know a bit about how it works and what malfunctions you should be on the lookout for.
1. Why do I need to have my A/C system serviced?
2. How often should the Vehicles A/C system be Inspected/Serviced?
3. Why does my fridge at home not need servicing every twelve months?
4. Is it true that the Vehicles A/C system should be run often throughout the year?
5. What’s involved in a service?
6. Why can’t I service the system myself?
7. Why put Ultra violet (UV) dye in the system?
8. Why use Nitrogen for leaks testing?
9. How do I know which gas is inside my vehicle’s A/C system?
10. Why should my gas be analysed?
11. What is Retro-fitting?
12. What causes the smell in my vehicles A/C system?
13. Does my vehicle’s A/C use more petrol?
14. What are the benefits of air conditioning?
15. What’s the best way to run my vehicle’s air conditioner?
16. Why is there pool of water under my car after using the A/C?
17. Can I use the A/C system to defog my car?
18. Why do I need to use an exact amount of Freon?
19. What is a "Liquid Charge", and why is it dangerous?
20. What causes clutch failure?
21. What causes compressor failure?
22. Why should I use R134a refrigerant?
23. What does humidity have to do with my air conditioner?
24. Where does the "High Side" begin?
25. Just what is this "Black Death"?
26. What exactly does a drier dry?
27. What is your position on flushing?
28. What about system leaks?
29. What does all this A/C jargon mean?
30. What is a ton of refrigeration?
31. How many different condensers are there, and which can be flushed?
32. What causes excessive clutch cycling?
33. Why should I worry about ESD?
34. Can compressors take all that heat?
35. Does it matter what oil I use?
36. What are the "Three laws of air conditioning"?
37. What should be done when installing a compressor?
38. How does an automotive A/C system work?
39. What about "Low Air flow"?
40. My clutch (or switch) does not function, what can I do?
41. Is a little moisture in the system really such a big deal?
42. What are the basic A/C systems?
43. How are clutch cycling switches different?
44. Are your compressors compatible with R134a?
All vehicle air conditioning systems leak to a lesser or greater degree. The losses occur through refrigerant escaping through the pipe joins as a result of vibration and ageing of rubber hoses and 'O' ring seals, as well as through the seal on the front of the compressor shaft.
An Annual Inspection is sufficient to check system condition and overall performance. A Service of the system should be carried out at least every two years even if it appears to be working well. It is estimated that you lose between 20-30% of the initial gas charge over a two year period and this figure is based on new vehicles. Keepin Cool Auto Air Conditioning Specialist can provide a comprehensive list of all checks carried out and produce a report on the condition of the system.
A domestic fridge has no rubber pipes and no seal on the front of the compressor shaft; all piping is copper therefore there is no leaking through pipe walls.
Yes, this helps to keep the system well lubricated and leak tight.
Because the refrigerant actually carries the oil that lubricates the system, most importantly the compressor. It also keeps the seals and hoses moist, thus preventing them from drying out andcracking leading to leaks.
We measure the pressures in the system, check quality of refrigerant present with a Gas Analyser and check all functions. Then we recover the refrigerant and vacuum the system down to a very low pressure (Deep Vacuum process) to remove any moisture that might be present. We then Re-Charge (Re-Gas) with virgin or re-cycled refrigerant R134a and also add a measured amount of the correct type of lubricant for your system. We also add Ultra Violet dye to help find any leaks that may develop in the future.
This is difficult not only because specialist equipment is needed but most importantly the refrigerant present in the system must be recovered. It is ILLEGAL to vent the refrigerant into the environment. Under Australian laws to protect the environment, the use of depleting substances and synthetic greenhouse gases is regulated. The licensing system ensures that only technician with adequate licences are allowed to service the vehicle's AC systems. People operating without licence or authorisation are committing an offence and are subject to prosecution. More information is available at Australian Refrigeration Council Website. The system is also under high pressure and needs pulling into a deep vacuum to remove any moisture. The refrigerants themselves have a very low boiling point and will cause freeze burns if they come into contact with skin or eye tissue. You have been warned!!!.
The UV dye shows up under a bright UV light source. So any leaks present in the system can be easily identified either during fault finding or if future leaks were to develop.
We use Oxygen Free Nitrogen (OFN) for leak testing. It would be illegal to re-gas a system to use the refrigerant as a means of leak detection. The pure form of Nitrogen is a naturally occurring gas in the air that we breathe and so is safe and legal to use. The Nitrogen is inserted into the system under high pressure thus simulating a system in operation and revealing any leaks in the system.
Generally all vehicles manufactured prior to 1994 used R12 and all vehicles manufactured after 1994 use R134a. Re gassing of the vehicles with R12 is prohibited as this refrigerant destroys the ozone layer. If your vehicle uses R12 it needs to be retrofitted to R134a
Our Gas Analyser can reveal whether or not your gas is the correct type for your vehicle air conditioning system and whether or not it is contaminated with other gases or has air in the sample which would strongly suggest a leak in the system.
The wrong type of refrigerant could also bring about the premature failure of the compressor as it may not be able to carry the essential lubrication around the system.
The term Retro-fitting is used to describe the procedure used to convert a car air-conditioning system designed for use with R12 refrigerant, to be modified to operate using R134A.
All retrofitted systems must include refrigerant labels that specify which refrigerant is used. This helps prevent contamination of air conditioning systems and refrigerant supplies.
Replacing service fittings:
All retrofitted systems must use unique fittings that match the refrigerant used.
Adding and recycling refrigerant:
During the retrofit procedure, the original refrigerant (CFC-12) is reclaiming in one of our dedicated recovery cylinders. Once full, these cylinders are then sent off to Refrigerant Reclaim Australia to be destroyed. New refrigerant is then added. Depending on the retrofit, additional parts may have to be replaced or the system components altered.
Note: Technicians handling air conditioner refrigerants must be certified by the Australian Refrigeration Council (ARC tick).
Health Warning: It has been known for systems to be Re-Charged using Hydrocarbon based refrigerants e.g. propane or methane mixtures. This basically means you could be driving around with a potentially lethal mix of gases in your system which in the event of a crash could explode with disastrous results.
Keepin' Cool does not recommend the use of hydrocarbon refrigerants or refrigerant blends of any kind in automotive air conditioning systems that are not designed specifically for their use. Read the Queensland Government safety alert
If you suspect your system may have been Recharged by a less than professional operator have Keepin' Cool run a check for you. Better to be safe than sorry.
Back to the Top
The origin of the smell is caused by fungus, bacteria and other microbes growing inside the evaporator core. The moisture-laden environment is very conducive to the growth of these organisms. As automakers downsize components to save space and weight, this problem has been increased. Because the automakers made the evaporator smaller, they added more fins and packed them closer together to increase the efficiency of the evaporator. While this has made the evaporator more efficient, it has also made it more prone to trap moisture that contributes to the growth of these organisms. We offer a full odour removal service using the latest research, tools and equipment. Contact us to find out more.
The answer to this is 'yes' it does, but not by much. But then think of the alternatives. You could have the windows open but that would increase wind resistance which can add up to 10% to your fuel consumption, especially at speed. And don't forget the extra noise and pollution through that open window. Also, it's worth pointing out that you should run your air conditioning at least once a week, especially in winter as the seals can seize up through non-use potentially costing you more in future in new parts and repair!!!.
- Efficient cool air in summer!
- Warm dehumidified air in winter easily demists steamed up windows!
- Filters pollutants / airborne particles in pollen helping allergy sufferers!
- Pleasant and odour free vehicle atmosphere at all times.
Turn the air conditioning on, ensuring that it's not set to 'economy' mode. When you first get into a hot car, open the windows, ensure that the air vents are set to face level and the system is set up to do the same, not pointed at your feet. Remember cold air falls. Turn the temperature to as low as it will go, and the blower as high as possible. Also make sure that the air is on 'recircle' mode and not taking air from outside. Better to cool already cooled air!! When the temperature is more comfortable, close the windows and increase the temperature to a more suitable level as well as decreasing the blower speed. You should also point the air vents upwards to ensuring the cold air flows down again.
If you see a puddle of water on the ground, usually under the passenger area do not be alarmed. This is a normal feature of the system as it is only water dripping from the air conditioning evaporator. The evaporator has a drain tube fitted to allow the condensation from the evaporator to drain away from the vehicle.
The A/C system is far more efficient than the heater at defogging the windows of your car in damp weather conditions - turn it on along with your heater for clearer views! (Once your car's engine is at normal operating temperature, running the heater and the A/C together will produce warm, dry air).
Today's auto air-conditioning systems use smaller amounts of Freon. No longer is it 900 to 2000 grams, but rather 450 to 1000 grams. With tight compressor tolerances and lubricant mixed with the Freon, the mixture must be just right to enter the compressor as a mist. Wrong mixtures will either under lubricate or slug the compressor causing premature failures. You don't know how much liquid Freon is in a system so you should recover the old Freon, evacuate and add the correct charge. Always check the OEM spec for the correct charge.
A "Liquid Charge" is any charging of the A/C system using Freon which enters the A/C system in a liquid state as opposed to a gaseous or Vapour state.
Warning! Charge A/C System with Freon as Vapour, not Liquid!
If a charging hose is long enough you might get away with using liquid refrigerant because the liquid will partially change to a gas in the hose. The odds are not in your favour. More often you will freeze and shatter the compressors valves when the refrigerant hits the valves as a liquid. This happens in mere seconds, which is why we recommend charging the A/C system with the engine off.
Some common causes for clutch failure:
1. Bearing failure.
2. Air Gap: Between the outer plate (hub) and the belt/rotor (0.406mm -0.762mm) Note! Air gap varies with compressor type - check OEM specs.
3. Shorted Coil - Due to improper polarity or weak/burnt winding.
4. Low voltage at coil will cause coil to overheat due to slippage.
5. Locked Compressor: Excessive discharge pressure - Check for restricted condensers, receiver/driers or an oil over charge
6. Belt is wrong type, wrong size, miss-aligned or loose.
Some common causes for compressor failures are:
LACK OF USE:
Compressors not run regularly will be starved for lubrication when they are turned on. This causes excessive ware until the oil again reaches the compressor. It's best to use the A/C once a week for a few minutes.
FAILURE TO FLUSH SYSTEM:
Compressors and hoses wear causing bits and pieces to mix with the oil. This sludge gets into the compressor and can cause it to seize. Failure to properly flush or using flush that leaves a residue is a primary cause of failure.
EXCESSIVE HIGH OR LOW PRESSURE:
Condenser fans can quit due to bad connections or defective motor winnings that get too hot. This creates excessive head pressure and heat that can lock up or damage a compressor. Loose connections at the coil can cause high resistance and low voltage causing clutch slippage. Low refrigerant charge will cause lack of lubrication getting to the compressor. Painting condensers will insulate them from efficiently removing heat and increase head pressure in the compressor.
IMPROPER FREON OR OIL CHARGE:
Compressors manufactured after 1990 have smaller capacity, therefore use less refrigerant and oil and are extremely sensitive to inadequate amounts of oil. The wrong type of oil may break down in high heat conditions. R134a systems are more sensitive to lubrication than R12 systems. An over charge of oil can clog the condenser, the orifice tube or expansion valve and starve the compressor of oil. R12 systems use mineral oil and R134a systems use PAG 1 or PAG 2 Oil (always check the OEM specs)
They can affect seals and O-rings, causing them to leak, swell or otherwise deteriorate and it can happen relatively quickly.
R12 has the ozone depleting chemical chlorine in it and has been replaced with a refrigerant known as R134a. A boiling fluid absorbs heat and changes its state to a vapour. The expanding vapour/gas has a lower pressure than the liquid and therefore lower temperature. For heated air to be absorbed it must transfer to a cooler surface. The trick is to find a liquid that boils at such a low temperature that the vapour is cold enough to absorb the amount of heat generated inside an automobile. Freon-12 boils at -30º C and its expanding vapour, in the evaporator core, absorbs the heated air circulating around it. Freon-134a boils at about the same temperature as R12 and therefore is a good replacement.
You're A/C unit works to remove heat from the passenger area and in doing so it also removes moisture. We are most comfortable when the relative humidity is closer to 20 precent than 90 precent, therefore the A/C system expends most of its effort wringing moister out of the air. This is what air conditioning is all about - conditioning the air. It's important to check the condensation drain at the bottom of the evaporator. If you see clear water dripping from your car, when parked… it's a good thing…if it's from the evaporator.
Where ever the dam is located is the separation point. We call it a dam because it has high pressure on one side and low pressure on the other. This separator is called an Expansion Valve or an Orifice Tube. Its job is to allow only enough refrigerant through to allow gas expansion in the evaporator. By limiting the flow of gas it creates the high pressure back to the compressor.
Black Death, as it is known by A/C techs, is a result from the breakdown of the refrigerant-lubricant. This causes excessive wear inside the compressor and the excessive wear causes a black residue that is actually a combination of solder flux from the condenser and aluminium shavings from the old compressor. When this sludge cools, it hardens in the condenser. Repeated flushing will not remove it, however, when the system is charged and running it liquefies, flows out into the liquid line and clogs the orifice tube. With less refrigerant flowing, past the orifice tube, the compressor is starved of lubricant and will lock up. The only answer is to replace the condenser.
It's not the Freon!! It's the oil in the refrigerant that absorbs moisture and holds debris in the system. Replacing the drier or accumulator, in addition to evacuation, will assure better performance.
Oil, sludge and debris that are left in the system can clog the condenser, orifice tube or expansion valve and damage the compressor. Flushing can remove excess oil and debris from previous services. You do not want to add yet another charge of oil while leaving unknown amounts of oil in the system.
Only flush a condenser that capable of being flushed. The answer to question #14 deals with this problem in greater detail.
At one time Freon was cheap and a 2oz. per year leak was acceptable in an 800-2000 gram system. Today systems are smaller and 1/2oz makes a big difference in performance. Good halogen leak detectors will show most system leaks, under static conditions, however some will leak only when the system is in operation. This is where the insertion of a florescent dye can help find the leak. Note, to see the dye stain you need a UV lamp and the leak has to be where the light can reach it. Most car manufactures approve the use of trace dyes and some OEM's have been inserting trace dyes on the assembly line. Dye can be inserted either when charging or when the system is charged. The amount of dye used is less than 5 ml. and remains in the system even if the total charge is lost. The dye stains the oil not the Freon and only flushing will remove it.
Glossary of Terms:
ACCUMULATOR: stores & filters Freon (on Low side of system)
BTU: British thermal unit
AMBIENT AIR: outside air
CAPILLARY TUBE: gas filled temperature-sensing tube
CCOT: clutch cycling orifice tube that replaces the TXV
CLUTCH CYCLE SWITCH: evaporator temp controlled switch that cycles clutch
COMPRESSOR: pump that moves the refrigerant.
CONDENSER: heat exchanger-removes heat from refrig
DISCHARGE LINE: compressor outlet line
DRIER: filters refrigerant (located on High side of system)
EPA: Environmental Protection Agency
ESD: Electrostatic Discharge
EVAPORATOR: heat exchanger-removes heat from air
HEAT: anything above absolute zero has heat
HEAT EXCHANGER: device for transferring heat
LIQUID LINE: moves high-pressure liquid through system
MANIFOLD: connects suction & discharge lines to compressor
PAG: Polyalkylene glycol (lube used with R134a refrigerant)
PROM: Programmable Read Only Memory - use in computers
SUCTION LINE: between evaporator outlet and compressor
TXV: Thermostatic Expansion Valve - maintains evaporator
Back to the Top
One Ton of refrigeration is defined as amount of heat (288000 Btu's) required to cause a change in state of one ton of ice to one ton of water at 32 degs. F in 24 hours.
A/C units are rated by Btu/hour ratings. A one ton unit is rated as 12000 Btu's (288000/24) The average factory installed auto A/C unit is rated at 1-3/4 ton.
R134a condensers have more fins/inch than R12 condensers and their fin diameters are smaller.( 6mm)
TUBE and FIN: Oldest industry standard, 3/8-inch diameter round tube condenser. Ok, for R12 but not recommended for R134a. This type of condenser is flushable.
6 mm Multi-Flow: smaller, lightweight and more efficient than 3/8-inch tube and fin and serpentine. Used in many domestic OE applications. This type of condenser is flushable.
SERPENTINE: All aluminium, more efficient than tube and fin, used on smaller imports where space is limited. This type of condenser is not easily flushed, replacement is recommended.
PARALLEL FLOW: all aluminium, this efficient design breaks up flow into tiny streams that give up heat more rapidly. This type of condenser is not flushable, replacement only!
PARALLEL FLOW with SUB Condenser: Oval tube multi-flow and sub-condenser stacked up. Refrigerant flows through the multi-flow into the drier (called a modulator) then continues as a liquid into the sub-condenser. This type of condenser is not flushable, replacement only!
It's common to assume low refrigerant is the cause for excessive clutch cycling and this often leads to adding refrigerant and thereby overcharging the system. Most vehicles have a compressor clutch cut out strategy based on an engine coolant temperature of 140.C–116.C. The vehicles computer relies on a coolant temperature sensor to provide the signal for the compressor clutch decision and if the sensor reads too high the clutch will cycle off. Cooling systems with a 50-50 anti-freeze mix and the proper radiator cap should boil at around 134.C, so the system may not be boiling when the compressor cuts out. Check the actual coolant mix and temperature by using an Infrared thermometer to check coolant temperature and a Scan Tester to tell you what temperature the sensor is actually signalling to the computer.
During the testing and repair of computer controlled vehicles we come in contact with components that may be damaged by ESD or static electricity. When installing new electronic components, the part itself may have developed a charge from contact with the package during handling; therefore you need to ground yourself to the body ground of the vehicle. This is easily done by using a wrist strap that is available at most electronic supply stores.
A compressor can take the heat, but if there's a condenser airflow problem, overcharge, poor lubrication, restriction, etc., the temperature can greatly rise and cause the compressor to seize. Some vehicles have compressors mounted low in the engine compartment and due to poor airflow the compressor can overheat and fail.
The moving parts of a compressor must be lubricated during operation. The oil is absorbed into the refrigerant that carries it through the compressor as a mist. Oil over/under charge can damage the compressor. Compatibility of refrigerant oil is determined by its ability to remain oil when mixed with the refrigerant and not become separated by a chemical reaction. R12 systems use a non-foaming sulphur-free grade of mineral oil 5gs formulated for that refrigerant and cannot be used in R134a systems. R134a systems use either synthetic oil PAG 1 or PAG 2 oil.
Everything has heat except at absolute zero (-238.C)
LAW I: to refrigerate is to remove heat - the absence of heat is cold.
LAW II: heat is ready to pass to anything that has less heat - nothing can stop the flow, you can only slow it down
LAW III: if a change of state is to take place there must be a transfer of heat - If a liquid is to change to a gas it must take on heat.
- Flush, with an approved solvent, to Clean the system
- Replace the Accumulator/Drier or Orifice tube
- Replace manifold sealing washers or O-rings
- Use a Vacuum Pump (20+ minutes) to remove moisture
- Add the proper amount and type of oil. Check OEM spec
- Rotate compressor hub 12 times to oil the shaft seal
- Place a strong external airflow into the condenser
- Check OEM specifications for correct refrigerant charge
- Charge with VAPOR refrigerant and with A/C and engine off
- Do a leak test and check voltage at clutch coil
- Check belt tension and alignment
- Check system operation at 1500 RPM and mid-blower speed
- Use gauges to check the system pressures.
- Only if the condenser is the type that can be flushed.
All matter has a certain amount of heat except at absolute zero 238.C). Ice cubes feel cool to the touch, but actually it just has less heat than your hand. Heat is transferring from your hand to the ice cube. This is the principle behind how an A/C cools the air in a car. Heated air is circulated across a gas filled evaporator and is transferred to the refrigerant gas making the air less hot. The heat-laden refrigerant then is drawn into the compressor, is super-heated by compression and forced through the condenser where the cooler outside air takes the heat from the refrigerant. Its next stop is the expansion device (TXV or Orifice tube), which meters refrigerant into the evaporator where it expands into a gas and it starts over again.
- The complaint: "it used to blow harder". Things to check are:
- Low blower motor voltage due to a poor ground
- Blower wheel loose on motor shaft
- Defective blower relay
- Air leak or obstruction in air duct system
- Air mode door directing some of the flow to the heater outlet
- Icing evaporator core due to condensation.
- Debris in evaporator housing that blocks air circulation.
- Obstruction at the air return
Electronic circuits are sensitive to voltage drops and operate in narrow voltage ranges. Many connectors have small spade or pin type connections and are engineered to have near zero resistance. If the connection is even slightly loose it will affect the voltage. What may seem to be a defective component could be a bad connector. The problem may be corrosion and careful brushing or using an electrical contact cleaner may cure it. Many OEM harness connectors are available as replacement parts.
Moisture causes internal icing that obstructs the orifice tube or expansion valve. This can create excessive high pressures and low cooling. The A/C system is a closed loop system so why does it need a Drier to remove moisture? Here's how moisture gets into the system. Refrigerant charged through service hoses not evacuated after being connected to the system will have air and moisture in them. Hoses left uncapped while replacing components allows moisture to enter. Refrigerant oil is hydroscopic (water absorbing like a sponge) and left uncapped will have moisture in it. Recycling machines with old filters will not remove moisture from incoming refrigerant. Condensation created when the Low side of the system gets cold and then warms up when the system is turned off is absorbed into the system through the hoses. Systems low on Freon will pull moisture into the system when they go into a partial vacuum.
ORIFICE TUBE SYSTEM
Orifice tube systems use an Accumulator located in the Low side of the system.
EXPANSION VALVE SYSTEM
TXV systems use a Drier located in the High side of the system.
Back to the Top
The clutch cycling switch for R134a vehicles has been calibrated for the slightly higher pressure of R134a. The threads, on the switch fitting, have been changed to metric to avoid connecting to a R12 system.
All of our compressors are remanufactured with retrofitting in mind. Each compressor is remanufactured with HNBR seals which allow the compressor to be installed in R134a refrigerant systems.