Car air conditioning system operation

Air conditioning is a system used to create and maintain a comfortable driving environment inside a vehicle. It does this by transferring the heat from inside a vehicle to the outside keeping the temperature down inside the car.The system cools, dries and cleans the air.

The most basic systems have manual temperature control but systems are becoming more and more complex with full climate control on a lot of modern cars which rely on a lot of sensors to maintain the selected temperature.

Air conditioning system schematic diagram-basic system

Common Air conditioning problems

Air conditioning system not cold enough

The Air Conditioning system in your vehicle is not usually covered by most manufacturers servicing schedules and the refrigerant gas that is used to operate the system depletes over time. On average most vehicles lose up to 15% per annum this problem can be caused when then system is not used during the winter months allowing the small “O” ring seals to dry out resulting in a gradual deterioration in system performance eventually resulting in the system being too low to operate at all.

Most problems of this type can be put right fairly easily by a leak check of your system followed by a complete refill of your air conditioning refrigerant, this is sometimes referred to as a re-gas. Please contact usfor your air con annual service or re-gas if you live in the Cardiff,Swansea, Bridgend or Newport area.

Air conditioning system smells odd

If you notice any strange smells when you put your air-con on then this could be signs of bacteria build up on your system.

As systems become older or are used infrequently the air conditioning system can start to develop bacteria, micro organisms and even mould or fungi growing especially behind the dash panel on the evaporator, this can lead to some very unpleasant odours. Some even claim this can result in headaches and flu like symptom sometimes referred to as sick car syndrome.

Don’t suffer any longer air con systems can be treated effectively with an anti-bacterial treatment that destroys the bacteria growth and leaves your car smelling fresh again.

The earlier this is treated the better you will feel!

Please call for a quote. from one of our mobile air con repair technicians.

If your air-con system suddenly starts making noises you have not heard before it is very advisable to have a qualified vehicle air conditioning specialist to have a look at it.

Some noises could be early symptoms of a compressor failure (the compressor is the air conditioning pump).The compressor is usually the most expensive part on the system ranging from approximately £230 to £600+ and if the bearings in your compressor break down or if the compressor seizes up it also means that other components can become contaminated with metal particles A flush of the system would then be needed as well as replacement of the compressor, the receiver / drier and the expansion valve - quite a hefty repair bill!
Its not all bad news however - some noises are quite normal

There are 2 different types of air-con system operation some vehicles use a system where the compressor (pump) cycles on and off which means that there is a clicking noise heard every few seconds this is normal, however if this switching cycle changes noticeably or the air con is not very efficient this could be an early symptom of low refrigerant or low gas pressure.
Pool of water underneath the car after using air-conditioning
You will sometimes see a water puddle on the ground, usually under the passenger footwell area, this is a normal feature of the air conditioning system as it is only water dripping from the air conditioning evaporator which has a drain tube fitted to allow the condensation from the evaporator to drain away from the vehicle.
Damp carpet in the footwell or excessive misting of the windscreen

Sometimes the drain tube from the evaporator may become blocked or detached allowing the condensation to build up inside your evaporator if this occurs water will just build up inside your car to a point where there are damp carpets or misting / high humidity type problems.

Heating System (Cooling system 11)

You may have heard the advice that if you car is overheating, open all the windows and run the heater with the fan going at full blast. This is because the heating system is actually a secondary cooling system that mirrors the main cooling system on your car.

Heater plumbing

The heater core, which is located in the dashboard of your car, is really a small radiator. The heater fan blows air through the heater core and into the passenger compartment of your car.

A heater core looks like a small radiator.

The heater core draws its hot coolant from the cylinder head and returns it to the pump -- so the heater works regardless of whether the thermostat is open or closed.

For more information on car cooling systems and related topics, check out the links on the next page.

Fan (Cooling system 10)

Like the thermostat, the cooling fan has to be controlled so that it allows the engine to maintain a constant temperature.

Front-wheel drive cars have electric fans because the engine is usually mounted transversely, meaning the output of the engine points toward the side of the car. The fans are controlled either with a thermostatic switch or by the engine computer, and they turn on when the temperature of the coolant goes above a set point. They turn back off when the temperature drops below that point.

Cooling fan

Rear-wheel drive cars with longitudinal engines usually have engine-driven cooling fans. These fans have a thermostatically controlled viscous clutch. This clutch is positioned at the hub of the fan, in the airflow coming through the radiator. This special viscous clutch is much like the viscous couplingsometimes found in all-wheel drive cars.

Thermostat (Cooling system 9)

The thermostat's main job is to allow the engine to heat up quickly, and then to keep the engine at a constant temperature. It does this by regulating the amount of water that goes through the radiator. At low temperatures, the outlet to the radiator is completely blocked -- all of the coolant is recirculated back through the engine.

Once the temperature of the coolant rises to between 180 and 195 F (82 - 91 C), the thermostat starts to open, allowing fluid to flow through the radiator. By the time the coolant reaches 200 to 218 F (93 - 103 C), the thermostat is open all the way.

The open and closed positions of a thermostat

If you ever have the chance to test one, a thermostat is an amazing thing to watch because what it does seems impossible. You can put one in a pot of boiling water on the stove. As it heats up, its valve opens about an inch, apparently by magic! If you'd like to try this yourself, go to a car parts store and buy one for a couple of bucks.

The secret of the thermostat lies in the small cylinder located on the engine-side of the device. This cylinder is filled with a wax that begins to melt at around 180 F (different thermostats open at different temperatures, but 180 F is a common one). A rod connected to the valve presses into this wax. When the wax melts, it expands significantly, pushing the rod out of the cylinder and opening the valve. If you have read How Thermometers Work and done the experiment with the bottle and the straw, you have seen this process in action -- the wax just expands a good bit more because it is changing from a solid to a liquid in addition to expanding from the heat.

This same technique is used in automatic openers for greenhouse vents and skylights. In these devices, the wax melts at a lower temperature.

Pressure Cap (Cooling system 8)

The radiator cap actually increases the boiling point of your coolant by about 45 F (25 C). How does this simple cap do this? The same way a pressure cooker increases the boiling temperature of water.

The cap is actually a pressure release valve, and on cars it is usually set to 15 psi. The boiling point of water increases when the water is placed under pressure.

When the fluid in the cooling system heats up, it expands, causing the pressure to build up. The cap is the only place where this pressure can escape, so the setting of the spring on the cap determines the maximum pressure in the cooling system. When the pressure reaches 15 psi, the pressure pushes the valve open, allowing coolant to escape from the cooling system. This coolant flows through the overflow tube into the bottom of the overflow tank. This arrangement keeps air out of the system. When the radiator cools back down, a vacuum is created in the cooling system that pulls open another spring loaded valve, sucking water back in from the bottom of the overflow tank to replace the water that was expelled.

Radiator (Cooling system 7)

A radiator is a type of heat exchanger. It is designed to transfer heat from the hot coolant that flows through it to the air blown through it by the fan.

Most modern cars use aluminum radiators. These radiators are made by brazing thin aluminum fins to flattened aluminum tubes. The coolant flows from the inlet to the outlet through many tubes mounted in a parallel arrangement. The fins conduct the heat from the tubes and transfer it to the air flowing through the radiator.

The tubes sometimes have a type of fin inserted into them called a turbulator, which increases the turbulence of the fluid flowing through the tubes. If the fluid flowed very smoothly through the tubes, only the fluid actually touching the tubes would be cooled directly. The amount of heat transferred to the tubes from the fluid running through them depends on the difference in temperature between the tube and the fluid touching it. So if the fluid that is in contact with the tube cools down quickly, less heat will be transferred. By creating turbulence inside the tube, all of the fluid mixes together, keeping the temperature of the fluid touching the tubes up so that more heat can be extracted, and all of the fluid inside the tube is used effectively.

Radiators usually have a tank on each side, and inside the tank is a transmission cooler. In the picture above, you can see the inlet and outlet where the oil from the transmission enters the cooler. The transmission cooler is like a radiator within a radiator, except instead of exchanging heat with the air, the oil exchanges heat with the coolant in the radiator.

source http://auto.howstuffworks.com

Engine (Cooling system 6)

The engine block and cylinder head have many passageways cast or mach ined in them to allow for fluid flow. These passageways direct the coolant to the most critical areas of the engine.

Temperatures in the combustion chamber of the engine can reach 4,500 F (2,500 C), so cooling the area around the cylinders is critical. Areas around the exhaust valves are especially crucial, and almost all of the space inside the cylinder head around the valves that is not needed for structure is filled with coolant. If the engine goes without cooling for very long, it can seize. When this happens, the metal has actually gotten hot enough for the piston to weld itself to the cylinder. This usually means the complete destruction of the engine.

One interesting way to reduce the demands on the cooling system is to reduce the amount of heat that is transferred from the combustion chamber to the metal parts of the engine. Some engines do this by coating the inside of the top of the cylinder head with a thin layer of ceramic. Ceramic is a poor conductor of heat, so less heat is conducted through to the metal and more passes out of the exhaust.

 

source: http://auto.howstuffworks.com

Water pump (cooling system 5)

A water pump is an important part of the engine cooling system. It provides circulation of the engine coolant (antifreeze) through the cooling system (see the top picture).

A water pump pushes the coolant through the passages (water jackets) in the engine cylinder block and cylinder head and then out into the radiator. This helps to keep the engine from overheating; the hot coolant passes through the radiator where it cools down and then returns back to the engine.

A water pump is usually driven by the engine through the drive belt. Sometimes it's driven by a timing belt. A water pump consists of the housing with the shaft rotating on the bearing pressed inside.

At the outer side there is a pulley mounted on the shaft. At the inner side there is a seal to keep the coolant from leaking out and the impeller that acts like a centrifugal pump (see the lower picture).

Fluid (Cooling System 4)

Cars operate in a wide variety of temperatures, from well below freezing to we ll over 100 F (38 C). So whatever fluid is used to cool the engine has to have a very low freezing point, a high boiling point, and it has to have the capacity to hold a lot of heat.

Water is one of the most effective fluids for holding heat, but water freezes at too high a temperature to be used in car engines. The fluid that most cars use is a mixture of water and ethylene glycol (C₂H₆O₂), also known as antifreeze. By adding ethylene glycol to water, the boiling and freezing points are improved significantly.

	Pure Water	50/50 C2H6O2/Water	70/30 C2H6O2/Water
Freezing Point	0 C / 32 F	-37 C / -35 F	-55 C / -67 F
Boiling Point	100 C / 212 F	106 C / 223 F	113 C / 235 F

The temperature of the coolant can sometimes reach 250 to 275 F (121 to 135 C). Even with ethylene glycol added, these temperatures would boil the coolant, so something additional must be done to raise its boiling point.

The cooling system uses pressure to further raise the boiling point of the coolant. Just as the boiling temperature of water is higher in a pressure cooker, the boiling temperature of coolant is higher if you pressurize the system. Most cars have a pressure limit of 14 to 15 pounds per square inch (psi), which raises the boiling point another 45 F (25 C) so the coolant can withstand the high temperatures.

Antifreeze also contains additives to resist corrosion.

source: http://www.howstuffworks.com

Plumbing (Cooling System 3)

The cooling system in your car has a lot of plumbing. We'll start at the pump and work our way through the system, and in the next sections we'll talk about each part of the system in more detail.

The pump sends the fluid into the engine block, where it makes its way through passages in the engine around the cylinders. Then it returns through the cylinder head of the engine. The thermostat is located where the fluid leaves the engine. The plumbing around the thermostat sends the fluid back to the pump directly if the thermostat is closed. If it is open, the fluid goes through the radiator first and then back to the pump.

There is also a separate circuit for the heating system. This circuit takes fluid from the cylinder head and passes it through a heater core and then back to the pump.

On cars with automatic transmissions, there is normally also a separate circuit for cooling the transmission fluid built into the radiator. The oil from the transmission is pumped by the transmission through a second heat exchanger inside the radiator.

source: http://auto.howstuffworks.com

The Basics of Car Cooling Systems (Cooling System 2)

Inside your car's engine, fuel is constantly burning. A lot of the heat from this combustion goes right out the exhaust system, but some of it soaks into the engine, heating it up. The engine runs best when its coolant is about 200 degrees Fahrenheit (93 degrees Celsius). At this temperature:

• The combustion chamber is hot enough to completely vaporize the fuel, providing better combustion and reducing emissions.
• The oil used to lubricate the engine has a lower viscosity (it is thinner), so the engine parts move more freely and the engine wastes less power moving its own components around.
• Metal parts wear less.

There are two types of cooling systems found on cars: liquid-cooled and air-cooled.

Liquid Cooling

The cooling system on liquid-cooled cars circulates a fluid through pipes and passageways in the engine. As this liquid passes through the hot engine it absorbs heat, cooling the engine. After the fluid leaves the engine, it passes through a heat exchanger, or radiator, which transfers the heat from the fluid to the air blowing through the exchanger.

Air Cooling

Some older cars, and very few modern cars, are air-cooled. Instead of circulating fluid through the engine, the engine block is covered in aluminum fins that conduct the heat away from the cylinder. A powerful fan forces air over these fins, which cools the engine by transferring the heat to the air.

source: http://auto.howstuffworks.com

How Car Cooling Systems Work (Cooling System 1)

Although gasoline engines have improved a lot, they are still not very efficient at turning chemical energy into mechanical power. Most of the energy in the gasoline (perhaps 7 0%) is converted into heat, and it is the job of the cooling system to take care of that heat. In fact, the cooling system on a car driving down the freeway dissipates enough heat to heat two average-sized houses! The primary job of the cooling system is to keep the engine from overheating by transferring this heat to the air, but the cooling system also has several other important jobs.

The engine in your car runs best at a fairly high temperature. When the engine is cold, components wear out faster, and the engine is less efficient and emits more pollution. So another important job of the cooling system is to allow the engine to heat up as quickly as possible, and then to keep the engine at a constant temperature.

source: http://auto.howstuffworks.com