A/C Light Question

#1
Just got a used 99 corolla and loving the fuel mpg!

I have a funny question about the ac light. When I turn the vent knob to blow air out the defrost/feet, the ac light comes on. When I push the ac button the light gets brighter.

Why does it do this
 
#2
When the defrost in a car is turned on, it cycles the AC unit on to circulate lubricating oil through the AC compressor so it doesn't rust and seize. Otherwise, during the winter the AC compressor is much more likely to develop rust and corrosion from disuse, causing it to fail.
 
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#3
When the defrost in a car is turned on, it cycles the AC unit on to circulate lubricating oil through the AC compressor so it doesn't rust and seize. Otherwise, during the winter the AC compressor is much more likely to develop rust and corrosion from dis-use, causing it to fail.
so every time i blow air out the upper dash vents/defrost vents, it kicks on the AC compresser and killing my fuel mileage? i like my top vents, guess i could pull the ac fuse. i dont like the ac running when its not needed.
 
#4
It's a feature, not a flaw.

If running in defrost, the designers have decided the AC is needed. Fogged windows are due to humid air, AC removes the humidity.

On older models, a lot of owners cuss their slow, inefficient defrosters, when all they need to do is turn on their AC compressors. Read your owners manual.
 
#5
so every time i blow air out the upper dash vents/defrost vents, it kicks on the AC compresser and killing my fuel mileage? i like my top vents, guess i could pull the ac fuse. i dont like the ac running when its not needed.
Yes, when the defrost is used, the AC compressor is cycling on. If you pull the AC fuse, not allowing the lubricating oil to circulate through the AC compressor, the compressor will eventually fail. To replace the compressor, recharge the AC system, etc., will be approaching $1,000 if not more.
 
#6
If running in defrost, the designers have decided the AC is needed. Fogged windows are due to humid air, AC removes the humidity.

On older models, a lot of owners cuss their slow, inefficient defrosters, when all they need to do is turn on their AC compressors. Read your owners manual.
True that!
 
#7
Yes, when the defrost is used, the AC compressor is cycling on. If you pull the AC fuse, not allowing the lubricating oil to circulate through the AC compressor, the compressor will eventually fail. To replace the compressor, recharge the AC system, etc., will be approaching $1,000 if not more.
Im still confused, sorry lol.

When you say “cycling on” do you mean it runs non stop the entire time the heat is blowing out the top vents?

Also if I run the heat through the floor, the ac does not come on. Does this mean my ac system will eventually fail. Or basically if I use my heat with out the ac compressor running it will damage the ac unit?
 
#8
Yes, when the defrost is turned on, the AC is on, it's just not blowing cold air. When you have the floor heat on, the defrost is off, so the AC is also off. If the AC compressor were never run during the winter months, it would not be circulating lubricating oil throughout the compressor and rust/corrosion would occur inside the AC compressor. Then when warm weather comes along and you turn on the AC, uh-oh! :(
 
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