I've heard that car A/C doesn't work below a certain temperature
because if it's freezing out, the coils might freeze up. Yet the guy
at the dealer says, run the A/C to clear interior fog on the windows,
and doesn't make any exception for freezing weather. Could someone
explain what actually happens?
If the A/C doesn't kick in when it is freezing out, how come the A/C
light still lights up?
Don't know much about A/C's, but I'm pretty sure that the operating
temperature is not at 0 deg C. The coils aren't filled with water,
they're some type of liquid similar to freon. According to a website I
found, the freezing point of freon-12 is -158C. Maybe some other
fluids/lubricants would cause the A/C to seize before the coils would.
The AC will turn on at any temperature but won't cool if the ambient
temp is below around 5 C. At such low temperatures, the evaporator
would cool below 0 C and the water condensing on it would form ice.
Under cold conditions, the AC is useless for dehumidifying the air and
preventing fog on the windows.
While the main purpose of AC is to cool the vehicle in the summer, it
can be used in the winter to help warm it up. That's because the AC
puts a load on the engine, which then warms up faster, and that gives
quicker heat out of the heater. Of course this uses up more gas, so
turn off the AC when the interior is warm enough.
Yeah. So in the summer time, the evaporator runs at around 32F/0C, the
water vapor in the air condenses on the evaporator coils, forms
liquid, and drips out of the car.
But in the winter when it is say 0F/-18C, the water vapor turns to
frost on the evaporator coils. It can't drip out because it is solid
ice. The evaporator ices up. At least this will be true when the car
is first started if the A/C is on.
Ten or 15 minutes later when the interior warms up, the situation may
be different, but by then you won't need the A/C to dry the air,
because the dry air from the outside plus the heat is doing that.
Just trying to understand what is happening....
The best dehumidifier in winter is to turn OFF the recirculate, and pump
bone-dry air into your car, displacing the moisture from your wet floor
mats. Works best in areas where winter is DRY.
Your Owner's Manual says you should use the AC occasionally in the
winter to keep it lubed. It will only cut in above a certain under-hood
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