Why does a/c comp run on defrost?
 

I have never understood this and figured I would ask! But why does the a/c compressor run with the defroster? Any particular reason?

On an old gasser of mine I had unplugged it thru the winter and never seemed to have any problems & it didn't affect it any way...I haven't done it yet to the ol dodge but sure thinking about it...if nothing else, it helps relieve the engine a little....

Just curious!!

Keeps the AC system from freezing in the winter. :tu:

Thats a minor part of it. The main reason it runs is to dry the air that will be blown on your windshield, preventing it from fogging up.

Exactly. The A/C system collects condensation. Ever notice all that water dripping out of your truck on a hot day? Where do you think that water comes from? While the air is usually drier in the winter than the summer(also varies a good bit by location) there is still water in the air.

When that warm air hits the cold windshield that water would drop out and condense on the windshield if the A/C didn't run. Like I said, depends on your location and humidity levels as to how bad you need it.

Yep, this is the main reason...dry air speeds the defogging.

+ it keeps every thing in the ac lubed :tu:

^^^ The reason. To keep the AC compressor clutch lubed in the winter.

moisture removal!! it will fog up without it