What is this engaging/disengaging?

[flyin-lowe]

Sorry for the stupid question but as soon as we start my sons ranger (04 3.0) this bottom pulley starts engaging disengaging about every 5-10 seconds. Funny thing is I took this short video because I couldn't tell where the noise was even coming from. Once I got it on my computer I could see the front part of the pulley starting and stopping. If the fan inside (heat/ac) is off it doesn't do this. All the heat and AC functions seem to be working as they should just seems like this should be doing this all the time...

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[Uncle Gump]

That is your A/C compressor clutch

 

[flyin-lowe]

Thx, is it normal for it to cycle like that if the AC is not on?

 

[Uncle Gump]

Short answer... yes

The AC is use to dry the air before it blows into the passenger compartment.

 

[flyin-lowe]

OK thanks. I remember hearing back in the day that the AC would cycle when the defrost was on, that way it wouldn't go all winter without moving, since most use defrost in the winter. Just something I noticed since we have had this truck and not sure if it's louder or what but never really noticed it before on other vehicles.

 

[19Walt93]

The compressor will run in all positions except Floor, off and vent. If it's cycling fast it means the charge is low, yours looks normal. It's a bonus that running the compressor on defrost clears the windshield faster, it was done to reduce the compressor failures we used to see after the a/c wasn't used from October to May.