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Understanding your automobile heating, ventilation and air condition systems


Understanding your automobile heating, ventilation and air condition systems

Some people enjoy driving and others do it as a necessity. Either way we want to be comfortable when we drive. There are many accessories on vehicles that need our attention. The most important is your auto HVAC system. On a hot summer day, we want a nice, cool car and on a cold winter morning, we enjoy a toasty, comfortable car.

Regular maintenance and an understanding of your automobile HVAC system will help you circumvent expensive repair costs. From time to time the car's HVAC system needs to be recharged to bring it back to maximum efficiency. Leaks in your AC system may cause a loss of refrigerant. You MUST have it fixed before refilling it with Freon or refrigerant. Corrosion will cause the heater core (secondary radiator) to leak. This is easily detected when you see steam in the passenger compartment that fogs your windows. You will know there is a leak by the sweet smell coming from your vents. Unfortunately changing the heater core is difficult because it is usually squeezed into some pretty tight spaces under the dash.

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Your car's heater core creates the heat for your car's AC system. The heater core is a secondary radiator and it is part of the car's cooling system. We get cool air from the conditioning system of our car.

The first car produced with an actual refrigeration system was the 1940 model year Packard. Those AC systems were crude by today's standards. Since the 1940's, many improvements have been added to automobile HVAC systems, like automatic temperature control (ATC) that allow you to set the desired temperature and have the system adjust automatically.

You will hear of 2 different types of vehicle air conditions systems, the R12 and the R134a-based systems. R-12 systems contain ozone-damaging chlorofluorocarbons (CFCs). In 1992 a new type of refrigerant for automotive air conditioning systems began to appear. R-134a is ozone-friendly because it contains no CFCs. It is also nontoxic and nonflammable, and meets all of the Environmental Protection Agency's criteria for alternative refrigerants. R134a was adopted, and many say it was adopted solely because DuPont had a patent on it; Australia, incidentally, uses a cheaper and more efficient hydrocarbon-based system.

Your car's air conditioning system's main function is not to push cool air into the car, but rather to displace the hot air with cool air. Like any refrigerating system, its efficiency is based upon how well it removes the heat. Your car's AC system has to remove about 6,000 BTU of heat per minute. The AC compressor circulates a liquid refrigerant called Refrigerant-12 (Freon) or R-134a. R-134a is tetrafluoroethane, which is a refrigerant that has zero ozone depletion potential and thermodynamic properties similar to R-12. It has the formula CH2FCF3 and a boiling point of -26.6 °C (-15.88 °F). promotes the use of efficient, environmentally safe refrigerants.

Be careful if you decide to review or look at your car's HVAC system. 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 compressor moves the R-12 or R-134a from an evaporator, through a condenser and expansion valve. Then, it goes back to the evaporator. The evaporator is right in front of a fan that pulls the hot air out of the vehicle interior. The refrigerant makes the hot air's moisture condense into drops of water, removing the heat from the air. You will notice this water dripping under your vehicle, after you stop on a hot day. Once the water is removed, the cool air is sent back into the car's interior.

To make it simpler (or more complicated), you have a compressor. Its primary function is to compress and pressurize gaseous refrigerant. It takes in cool gas into its suction port and pressurizes it at its discharge port.

The compressor is powered by a drive belt from the engine. The compressor has an electrically operated engagement clutch to either turn the refrigeration operation off or on.

Then, the condenser is located in front of the radiator. Through the use of cool air flow provided by the engine fan, the condenser cools the hot gas and converts it to liquid. The liquid is still under considerable pressure and is warm, but not as hot or as high pressure as when it exited the compressor.

The expansion valve system handles the exiting liquid. It is sent via a small tube (also called a liquid line) to a drier (sometimes called a receiver).

The drier is a can with a desiccant bag inside. It looks about the size of a coke can, and is usually located very near the condenser outlet pipe. There is no pressure change or temperature change at the drier.

As the high pressure, warm liquid exits the drier; it passes through the expansion device, the pressure is reduced considerably; and the temperature drops also.

The next step is evaporator operation. As the cold liquid exits the expansion device, it is fed to a heat exchanger type device under the dash that blows warm air from the car interior across it.

The cold liquid refrigerant is what cools the air you feel coming out of the ducts. As the air is cooled in the heat exchanger, the liquid refrigerant is heated in the other side of the heat exchanger and then it evaporates.

The accumulator contains a desiccant bag also. The accumulator provides a similar function as the drier in the expansion valve system, but is located in the evaporator outlet instead. This positioning allows the accumulator to collect any un-evaporated refrigerant that may still be in the liquid state. It protects the compressor from liquid lock damage. The evaporated gas then returns to the compressor "suction" port to begin this whole process again.

If your auto's AC system is not cool enough it could be any number of things, these are the most common"

Dirty condenser - As you learned above, the condenser is the heat exchanger mounted in front of the radiator. It cools the high pressure refrigerant vapor after it exits the compressor so it can condense into a liquid. If the condenser is full of leaves, bugs and debris, air flow through the unit may be blocked to the point where little cooling occurs. Cleaning the condenser is an inexpensive, easy fix to your car's AC problem.

Low refrigerant - This cost is a little more, especially if there is a leak. Most states do not allow you to add refrigerant to a leaking system. The EPA regulates this.

Condenser cooling fan failure - The condenser often has its own separate electric cooling fan. This fan should come on and remain on when the A/C system is operating. If the fan motor, motor relay or wiring is defective, the fan may not be working.

Air or moisture contamination - For the refrigerant inside the system to do its job properly, it must not be contaminated with air or moisture. Air reduces the cooling efficiency of the system while moisture can freeze and form ice that causes blockages in orifice tubes and metering valves. Air and moisture contamination may be the result of un-repaired leaks in the system, or failing to vacuum purge the system prior to recharging it with refrigerant.

Blockages - Debris, rust or debris in the system may plug up the orifice tube or metering valve that admits refrigerant into the evaporator.

Mechanical problem - These include things like metering valve failures, compressor wear, a compressor clutch that fails to engage, bad pressure switches, etc. Pinpointing the problem will require the skills of a competent A/C technician

Good luck with your car HVAC system.


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1 Responses to "Understanding your automobile heating, ventilation and air condition systems"
  1. renaldhenares

    Of course everybody wants a comfortable trip. HVAC systems service of this country can helps us to have this.