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A/C And Heat Systems Overview #166862 Apr 27, 11:30pm Apr 27, 11:30pm
Joined: May 2002
Posts: 6,007
Los Angeles, CA
2001 Absolutely Red Toyota Celica GT
isaac OP
ECelica Admin
2001 Toyota Celica GT
isaac OP
2001 Absolutely Red Toyota Celica GT
ECelica Admin
2001 Toyota Celica GT

Joined: May 2002
Posts: 6,007
Los Angeles, CA
A/C And Heat Systems Overview
The Air Conditioning and Heating System

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 return 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.

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-12 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.

Heater/AC Blower Motor
The blower motor is the motor that turns the electric fan in an air conditioning or heating system.

Air Ducts
The air ducts control the passage of hot or cold air into the interior of the car. They are operated by a control on the dash, either manually or automatically.

Most air conditioning/heating systems have three possible air settings. One is to recirculate the air that is in the car, a second is to use only air from the outside of the car, and a third is to mix some of the outside air with the air recirculating inside the car.

Low Pressure Line
The low pressure line is a hose, or tube containing refrigerant that connects the evaporator to the air conditioning system's compressor. The compressor draws the low pressure refrigerant from the evaporator in through the low pressure line in order to compress it.

High Pressure Line
The high pressure line is a hose, or tube containing refrigerant that connects the air conditioning system's compressor to the condenser. The compressor forces the compressed refrigerant into the condenser through the high pressure line.


Re: A/C And Heat Systems Overview [Re: isaac] #166863 Apr 27, 11:40pm Apr 27, 11:40pm
Joined: May 2002
Posts: 6,007
Los Angeles, CA
2001 Absolutely Red Toyota Celica GT
isaac OP
ECelica Admin
2001 Toyota Celica GT
isaac OP
2001 Absolutely Red Toyota Celica GT
ECelica Admin
2001 Toyota Celica GT

Joined: May 2002
Posts: 6,007
Los Angeles, CA
A/C concerns & proper usage
When and if your A/C works real well, depending on the humidity, the system will create lots of water. For the first time in my memory, we are having problems created by that excess water.

The problem is inside the evaporator case which has the evaporator in it. The evaporator case is behind the glove box, it looks like a small radiator and it gets very cold. There is a fan behind the evaporator that blows air across the evaporator where it gets cold and is sent out the vents. The evaporator case is often two pieces of plastic screwed together and a foam gasket is often used.

Some say the mold or green slime that causes the stink is caused by the foam gasket. Others say the plastic is the problem and others simply say it's the water. To me, it really makes no difference, we know what makes it happen and we know how to make it better. I'm not a chemist nor can I explain why this is a problem today and has never been in the past.

I think that many of the A/C systems we have today work much better than years ago. Because of that, I think folks get cool faster and turn the fan down to a lower speed. Because the A/C works so well and because it is working so efficiently, the occupants will turn the fan down because they get colder faster.

This causes less air which causes wetness that otherwise would have been blown dry by the higher fan speed. The car ends up being parked with a very wet evaporator case and mold grows. The slime gets a foot hold in the case and this baby starts stinking.

As most of you know, you can choose air from two different places using your A/C controls. "Recirculate" or "maximum" air means the air from inside the car is drawn up through a vent near the passengers feet and run back over the ice cold evaporator core. "Outside" air is brought in from the vent just under the wipers just in front of your windshield.

Recirculating the air inside the car is exactly how your home A/C works. It draws the cool air in and cools it more and through attrition, you get the temperature you asked for.

When you choose outside air, you MUST drop a window a tad or your A/C will not work very well. It would be like pushing air into a closed car. You must give it a place to vent.


Knowing where the air is coming from helps you use your A/C the most effective way. Here is a few examples:

Car very hot, been sitting in sun all day
Hi blower, outside air and both front windows down about 3-4 inches for 5 minutes or so. That will help move all the real hot air inside the car up near the roof (because hot air rises) outside. Once you replace it with cooler air, which should take about 5 minutes or so, switch to "recirculate" or "maximum" and that will bring the inside temp down further.

A/C system stinks
Use outside air all the time and the highest fan speed you can stand. Make sure you have a window open to vent the car. This gives warm air to the evaporator case, keeps the moisture down and the high fan speed keeps the evaporator case dry.

Another thing you can do to keep the smell away is shut the A/C off when you get close to home, but put the blower or fan on high to dry the evaporator case before you park your car for the night.

Smoker sitting in the front passenger seat
Hi blower / outside air / drop the passengers' window 3-4 inches. This way you are venting the entire car out that window . . . along with the cigarette smoke.

Some tips on how to increase air flow can be found at...

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