This isn't a complaint, just wondering-when I turn my defrost on, my idle jumps up a bit. I know that it's supposed to for the a/c, but why for defrost? Also, every once in a while, it'll make a strange noise, almost like a rolling pop. Tough to describe, hopefully someone knows what I'm talking about. Why? What's wrong? Thanks.

 

The defrost kicks the A/C on as well.

From what I was told once, the defrost runs the A/ to keep the crap in the system circulated. Since one is inclined to not run the a/c during the winter months, having the a/c work w/defrost assures that it will keep regular use all year 'round which is supposed to help avoid premature failure of the compressor & comps.

Weather this person who (is a mechanic, not specifically for a/c tho) explained it to me was merely blowing smoke up my postierior or not,, it sounded logical.

As for as the 'rolling pop' (I'm guessing w/the A/C running),, that's the compressor cycling. The 'pop' or 'clack' is the magnetic clutch engauging.

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That actually makes a lot of sense to me. Back to the strange pop, it's not the clutch-I know how that sounds. This noise is definitely not supposed to occur.

 

It turns it on to dry the air. Blowing humid air at the windshield is gonna make it worse.