A Cars HVAC System by Kevin Schappell

A Cars HVAC System by Kevin Schappell

Not only do we depend on our cars to get us where we want to go, we also depend on them to get us there without discomfort. We expect the heater to keep us warm when it's cold outside, and the air conditioning system to keep us cool when it's hot.
We get heat from the heater core, sort of a secondary radiator, which is part of the car's cooling system. We get air conditioning from the car's elaborate air conditioning system.
Despite its relatively small size, the cooling system has to deal with an enormous amount of heat to protect the engine from friction and the heat of combustion. The cooling system has to remove about 6,000 BTU of heat per minute. This is a lot more heat than we need to heat a large home in cold weather. It's good to know that some of this heat can be put to the useful purpose of keeping us warm.
Air conditioning makes driving much more comfortable in hot weather. Your car's air conditioner cleans and dehumidifies (removes excess moisture), the outside air entering your car. It also has the task of keeping the air at the temperature you select. These are all big jobs. How do our cars keep our "riding environment" the way we like it?
Most people think the air conditioning system's job is to add "cold" air to the interior of the car. Actually, there is no such thing as "cold," just an absence of heat, or less heat than our bodies are comfortable with. The job of the air conditioning system is really to remove the heat that makes us uncomfortable, and returns the air to the car's interior in a "un-heated" condition. Air conditioning, or cooling, is really a process of removing heat from an object (like air).
A compressor circulates a liquid refrigerant called Refrigerant-12 (we tend to call it "Freon," a trade name, the way we call copy machines "Xerox" machines). The compressor moves the Refrigerant-12 from an evaporator, through a condenser and expansion valve, right back to the evaporator. The evaporator is right in front of a fan that pulls the hot, humid air out of the car's interior. The refrigerant makes the hot air's moisture condense into drops of water, removing the heat from the air. Once the water is removed, the "cool" air is sent back into the car's interior. Aaaaaah! Much better. Newer cars have R-134 as the refrigerant, but work in the same way as R-12.
Sometimes we worry when we catch our car making a water puddle on the ground, but are relieved to discover that it's only water dripping from the air conditioning system's condenser (no color, no smell, and it dries!).
Note: Refrigerant is extremely dangerous. Many special precautions must be taken when it is present. It can freeze whatever it contacts (including your eyes), it is heavier than air and can suffocate you, and it produces a poisonous gas when it comes in contact with an open flame.
The above information is directly from the Auto Insight program, which you can buy online from AutoEducation.com.
Common Problems:

From time to time the A/C system needs to be recharged to bring it back up to maximum efficiency. Sometimes a leak may cause loss of refrigerant and will need to be fixed before refilling. It's difficult to tell if a leak is present without specific test equipment so let it up to a professional.
Corrosion will cause the heater core (secondary radiator) to leak. This will manifest itself by leaving steam into the passenger compartment and fogging your windows. You will know there is a leak by the sweet smell coming from your vents. Unfortunately changing the heater core is usually not the easier job in the world, as engineers tend to squeeze them into some pretty tight spaces under the dash.

About the Author
Kevin Schappell maintains http://www.carbuyersclub.com where he gives advice on buying, selling, insurance, and financing. A mechanical engineer and car guy, Kevin has decided to spend his online time helping others learn about automobiles. To learn more about how your car works, Kevin has createdhttp://www.mycarwizard.com

Your Drive Train Explained by Kevin Schappell

Your Drive Train Explained by Kevin Schappell

The drive train serves two functions: it transmits power from the engine to the drive wheels, and it varies the amount of torque. "Power" is the rate or speed at which work is performed. "Torque" is turning or twisting force. Multiple ratio gearboxes are necessary because the engine delivers its maximum power at certain speeds, or RPM (Rotations Per Minute). In order to use the same engine RPM's at different road speeds, it is necessary to change the "Gear Ratio" between the engine and the drive wheels. Just like a bicycle, the car has to switch gears in order to move at a wide range of speeds. Unlike your bicycle, the car's drivetrain also has to allow you to back up. (Well, you could push it backwards if you ate your Wheaties)
There are actually two sets of gears in the drive train; the transmission and the differential. The transmission allows the gear ratio to be adjusted, and the differential lets the drive wheels turn at different speeds.
Manual transmissions usually have four or five speeds, and often have "overdrive", which means that the output shaft can turn faster than the input shaft for fuel economy on the highway. Some use an electric clutch and a switch that controls whether the overdrive is engaged or not. An interesting development on a few cars is the "clutchless" manual transmission, which uses a stick shift and an automatic electric clutch. Speed and position sensors, mini computers, and throttle controls keep the engine from over-revving when the driver shifts gears. As with many automotive "inventions", this is an old idea, which may now reach feasibility due to the computer revolution.
Automatic transmissions commonly use three forward gears to blend speed and torque. In the case of a three-speed transmission, first gear delivers maximum torque and minimum speed for starting. Second gear offers medium torque and speed for acceleration and hill climbing. Third gear allows maximum speed with minimum torque for highway travel. A reverse gear permits backward movement.
A transmission is a speed and power-changing device installed at some point between the engine and driving wheels of a vehicle. It provides a means for changing the ratio between engine RPM (Revolutions Per Minute) and driving wheel RPM to best meet each particular driving situation.
Some types of drive train layouts use a "Transaxle", which is simply a combination of the transmission and the differential. These are usually found on front wheel drive cars, but are also used on mid- and rear-engine cars. Some exotic cars have their engine in the front, and a transaxle in the rear of the car for better weight balance.
Torque is derived from power. The amount of torque obtainable from a source of power is proportional to the distance from the center of rotation at which it is applied. It is logical, then, that if we have a shaft (in this case, the crankshaft) rotating at any given speed, we can put gears of different sizes on the shaft and obtain different results. If we put a large gear on the shaft, we will get more speed and less power at the rim than with a small gear. If we place another shaft parallel to our driving shaft and install gears on it in line with those on the driving shaft, we can obtain almost any desired combination of speed or power within the limits of the engine's ability. That is exactly what an automobile transmission does by means of gears and other devices.
There are two types of transmissions; manual and automatic. If you have a manual transmission, you have to shift the gears yourself, usually with a stick located on your console and the clutch pedal. If you have an automatic transmission, the mechanism changes without any help from you. This is accomplished through a system that works by oil pressure. Each shift of the gears is controlled by a shift valve; the gears shift change depending on speed, the road, and load conditions.
Another basic component of all drive trains is some form of a clutch. it allows the engine to continue rotating while the gears and wheels are stationary. Automatic transmission cars use a "torque converter" in lieu of a clutch.
The last component in the drive train is the axle. In a rear wheel drive car the axle is in the rear. Engine power is transmitted from the transmission to the axle via the drive shaft. The drive shaft is basically a metal tube with joints on each end called universal joints. These joints allow the tube to move in relation to the suspension and keep power flowing to the rear. In front wheel drive cars the axle is integrated into the transmission thus the term transaxle.
From the back of the engine to where the rubber meets the road, the drive train encompasses one of the most complicated systems of your car. Some people say looking at a transmission "makes their brain hurt".
The above information is directly from the Auto Insight program, which you can buy online from AutoEducation.com.
Common Problems:

Manual transmissions suffer from wear mainly in the synchronizers. The synchronizers make shifting easier and help to prevent gear clash. Over time the synchronizers, which are made of brass, can wear out causing hard shifting and grinding.
Automatic transmissions can also wear out, causing slipping and uneven shifting patterns. Universal joints can wear and cause vibrations while driving. Many newer universal joints are sealed and cannot be lubricated, leaving replacement as the only option.
Preventive Maintenance:

Change the fluid in your transmission at recommended intervals. Your owners manual will give you a time schedule in miles and or months. If you tow a boat or trailer be prepared to change the fluid even sooner. Most owners manuals will give you recommend intervals for severe use like towing or off-road use.
Do not "ride" the clutch if you have a manual transmission. Learn to release the clutch in a smooth motion without revving the engine too much. Revving the engine too much while pulling out can cause premature wear on the clutch.
If you do tow a boat or trailer, consider getting a transmission cooler for your automatic transmission. Temperatures can approach the boiling point in severe conditions. Most newer trucks come equipped with transmission coolers if sold with a towing package.
Make sure your universal joint is lubricated at oil changes if they are the type, which can be lubricated. When replacing universal joints try to find replacements with lubrication fittings so you can lubricate in the future.
If you have a front wheel drive car, avoid applying the gas to the floor while the wheels are turned at full lock. This puts stress on the universals and can cause premature failure. This can happen when stuck in the snow and trying to get out.
What to discuss with your mechanic:

If you are noticing a vibration in the car while driving, make sure to describe when it happens. While accelerating? braking? maintaining speed? when turning?

About the Author
Kevin Schappell maintains http://www.carbuyersclub.com where he gives advice on buying, selling, insurance, and financing. A mechanical engineer and car guy, Kevin has decided to spend his online time helping others learn about automobiles. To learn more about how your car works, Kevin has createdhttp://www.mycarwizard.com