I have exactly the same problem. I checked under the dash and when I
twist the temperature control knob, I can see the lever that controls
the blend door move at its full range. When switching from cold to hot,
I get warm air for a few seconds, but then it slowly cools until it's
cool air, but not quite as cool as it is when it's on full cold.
I wondered if the heater core might be clogged, but in my past
experience with clogged heater cores, the windshield defogger wouldn't
defog the window effectively, yet this one does. It just does it with
cold air, but very quickly.
I just can't seem to figure this one out.
I have a '00 Taurus that I've recently had A/C problems, and in my
investigations, I found that the A/C compressor would engage when the
blend selector was set to include the windshield defrost vents
irrespective of the temperature control knob. I was told that this
was a feature so that any air going to the windshield would pass over
the evaporator and therefore be drier. My hypothesis would be that
even though you have poor heating of your defrost air, you are at
least passing _drier_ air onto the glass and therefore forcing
evaporation by virture of the humidity differential.
That doesn't really gel with your previous anecdotal experience,
Yes, this is all true.
My friend always gets mad at me when I run his A/C through the normal
dash vents with the temperature set to warm. He says I'm going to mess
up his air conditioner that way. I've explained to him a dozen times
that the only difference between running the defogger and the A/C is
that A/C comes out of the dash vents while the defogger comes out of the
windshield vents. The compressor runs on both, precisely for the reason
you describe. If my body is cold, then running "warm air conditioning"
from the dash vents keeps me warm while also keeping all the windows
His Oldsmobile Alero actually has a feature I wish I had on my Taurus.
He can run the compressor on ANY setting, including the foot heater
vents. His has a button to engage the compressor on any blend setting.
That would be nice in my Sable.
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