Compressor running when not turned on?

[bradleyheathhays]

I have an '02 Taurus with 85k miles on her that I just bought. Today when I was checking something under the hood I noticed this metal
line cold and dripping with water...

See the pipe with a white box around it.


I had the air on but turned to the position of arrows pointing out of the dash and floor vents only. The defrost or a/c function was
not selected. It seems to be doing it consistently. I haven't traced all the parts of this car's a/c system yet but I don't know
of anything else under a hood that turns cold and sweats. Why would my compressor be working when it's not selected? What
tests should I run?

[yuccales]

I always thought the a/c compressor would turn on when defrost was on to keep it lubricated during cooler weather. Thinking it's normal.... but what do I know.

[Steeveedee]

The AC runs during the defrost cycle to further dry the air, since defrost takes in only outside air, which could be saturated, if it's raining, for example.

[Andy4639]

All AC systems run when in defrost mode to dry the inlet air of moisture to keep the windshield clearer, they started this in early 90's on GM products. Not sure about fords.

[hairball]

Originally Posted by bradleyheathhays

I have an '02 Taurus with 85k miles on her that I just bought. Today when I was checking something under the hood I noticed this metal
line cold and dripping with water...

See the pipe with a white box around it.


I had the air on but turned to the position of arrows pointing out of the dash and floor vents only. The defrost or a/c function was
not selected. It seems to be doing it consistently. I haven't traced all the parts of this car's a/c system yet but I don't know
of anything else under a hood that turns cold and sweats. Why would my compressor be working when it's not selected? What
tests should I run?

There may be a relay in the clutch circuit that is stuck closed. It is usually located in the engine compartment fuse/relay panel. Others are correct saying that the compressor runs in defrost mode.

[bradleyheathhays]

Thanks everyone for the advice, but I'm not sure why I've gotten this many responses explaining why the compressor runs in defrost mode because my post indicates a condition where the compressor is running when selected for a vent only mode.

hairball you've got the jist. Thanks for the relay suggestion.

[68C15]

First with engine off I would try spinning the clutch face by hand. It should spin freely. Next I would hook up my scanner and see if the ECM is being told to engage clutch. But not having a scanner I would unplug the low pressure cycling switch. It's the one just to the left of your hose in question. The dash control sends power through that switch and then to ECM to tell it "driver requests AC, low presssure says it's good to operate safely". Visually look at compressor to see if the clutch face is turning. If it still is then its highly likely your el ctrical issue is upstream

[68C15]

Here is a screen shot from the diagram. The AC request circuit is on the left. Power comes in on red wire and out on violet wire to the low pressure cycling switch. This shows what switch positions it is d signed to operate AC

[hairball]

Originally Posted by bradleyheathhays

I have an '02 Taurus with 85k miles on her that I just bought. Today when I was checking something under the hood I noticed this metal
line cold and dripping with water...

See the pipe with a white box around it.


I had the air on but turned to the position of arrows pointing out of the dash and floor vents only. The defrost or a/c function was
not selected. It seems to be doing it consistently. I haven't traced all the parts of this car's a/c system yet but I don't know
of anything else under a hood that turns cold and sweats. Why would my compressor be working when it's not selected? What
tests should I run?

Just curious as to what you found?