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 stinkin'.
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:
Smoker 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.
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 "recirc" 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.
My A/C is coming out of the floor vents or the defrost vents instead of the dash vents, why? or "When the AC is running and you press on the accelerator the A/C seems to shut off." --- We use engine vacuum to control the doors in and under your dash that control where the air (warm or cold) comes out. The default position in almost all cars is either the defrost vents or the floor vent. So when you lose vacuum to the vents delivery controls, the air coming out of the vents will go to the default position.
There will be a vacuum line (rubber or colored hard plastic) from the engine. It may go to a round black storage pod, in and out and then into the firewall and disappear. The easiest way to find this circuit is find and follow the vacuum line that goes through the firewall.
The vacuum is delivered to the dash controls or the mode switch. The mode switch is the lever that changes the climate controls to A/C, A/C Max, heater, defrost, etc. If that mode switch is bad, it will leak vacuum and that can cause your vents to go to default.
From the mode switch, the vacuum is delivered to numerous doors and pods that redirect the warm or cold air.
The most common area of concern (60%) is under the hood. The vacuum port on the intake manifold can be plugged with carbon, the storage pod can have a leak or be plugged, the vacuum line can be cut, pinched, broken, split, anything that will allow vacuum to leak and not be delivered to the dash controls.
The second most common area of concern (25%) is a bad mode switch and other areas make up the last 15%.
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