Car Automotive

The elaborate system of ducting under the dashboard of your vehicle is designed to put heated or air conditioned air right where you want it. Most vehicles have ducts that allow the driver to direct the heated or cooled air toward the floor, the front seat occupants or the inside of the windshield for defrosting, or a combination of the above. Air is forced through various vents in the dash via a series of cable or vacuum operated doors. Usually, the more expensive the vehicle, the more elaborate the duct system.

The cable system is virtually foolproof. Cables rarely have to be replaced during the service life of the vehicle. The first tip-off that something is wrong with a cable usually occurs when it becomes difficult to move the control lever on the control head for the heater and air conditioner. If this happens, the door at the other end of the cable is probably jammed. Don’t try to force the lever or you’ll probably break the cable. Instead, refer to the Haynes Automotive Repair Manual which covers your vehicle, remove the dash or under dash trim plates and try to free up the door.

Some heating and air conditioning systems utilize vacuum lines instead of, or in addition to, cables for actuating the doors. And the latest designs employ electrically actuated doors, or a combination of electrical and vacuum operated doors . These systems are highly complex and their diagnosis and repair is sometimes even beyond the scope of professional mechanics! Service on such systems is best left to an air conditioning technician.

The compressor is the pump that circulates refrigerant through the system.The suction side of the compressor pulls in refrigerant in a low pressure,low temperature form. The refrigerant is then pumped through the compressor to the discharge or outlet side where it’s compressed, raising its temperature.It’s now ready once more to condense and release heat. The pressurized,heated refrigerant vapor is forced out of the compressor, through the high pressure line, to the condenser.

Basically, all compressors fall into one of two categories: piston type and rotary vane type. As the name implies, piston type compressors have one or more (up to ten) pistons arranged in either an inline, axial, radial or vee configuration.Rotary’vane compressors have no pistons.

Piston type compressors go through an intake stroke and a compression stroke for each cylinder. On the intake stroke, the refrigerant from the low side (evaporator side) of the system is drawn into the compressor. The intake of refrigerant occurs through reed valves. These one-way valves control the flow of refrigerant vapors into the cylinder.During the compression stroke, the gaseous refrigerant is compressed.

This increases both the pressure and the temperature of the heat-carrying refrigerant.The outlet (discharge) side reed valves then open to allow the refrigerant to move into the condenser. The outlet reed valves may be considered the beginning of the high side of the system.

When viewed in its broadest sense, energy takes many forms, manifests itself in many ways and can be transformed from one form to another in many complex ways. But heat is always there in some way. Let’s take a few examples. The sun, obviously, gives off vast quantities of energy, heat being one of the more obvious ones. On a smaller scale, any fire also gives off heat. The connecting rods, crankshaft and drivetrain of an internal combustion engine convert the chemical energy released in the explosion of gasoline vapors into the kinetic energy of the moving automobile, in the process creating a lot of heat because of the friction created by all those moving parts rubbing against one another. And every time the driver applies the brakes to stop the vehicle, the friction generated between the brake pads and rotors, and between the tires and the road, transforms the kinetic energy of the moving vehicle into heat.

But when you hear the word “heat,” do you think of kinetic energy, friction, internal combustion, fires or the sun? Probably not. The first thought that crosses your mind is the palpable effect of heat on your body when you are in close proximity to a heat source. In other words, the word “heat” makes you think of the physiological sensation of being hot. That’s because we humans are pretty sensitive to heat, or the absence of it.