So, I'm in the drive-thru at McNasties . . .
 

. . . just sitting in my truck waiting for the car in front of me to advance forward so I can pay for my Quarter Pounder and fries. While in line, with the window down, I keep hearing this clicking sound from my engine while it's idling. It clicks, kind of makes the engine idle differently, then about a minute later it clicks again and does the same thing. I know it's not my AC running because I don't have the AC turned on. I heard this same sound on Saturday as well while it was idling.

What's going on do you think? Is that normal?

Year of truck? Engine?

its your idler pulley engaging and disengaging. its normal my truck does the same thing.

or your fan clutch

your ac could be running. if you have your selector on either of the two defrost settings your ac will kick on.

idler pulley engaging? what does an idler pulley do when it engages?

It's a 1999 Mazda B4000 auto 4L with 100K on it. I've had it all of just one week.

Thanks.

What's a fan clutch and is it suppose to be doing that?

yup it the AC compressor. if you have the blower blowing on both ur head and feet at the same it will run the compressor. even though it is to the right of the off setting it is still the AC. mine does that too and i have not had it blow up....yet.

Hmmm. That may be it. It could have been in the defrost position. I know I had the heater fan running on low.

That may account for my crappy gas mileage as well.

it turns the fan on and off to cool your radiator

AC pump is off in "floor only" and "off", all others its on.

"its your idler pulley engaging and disengaging." -WTF? Um, no.

You mean there's no "vent" on this truck without also running the AC compressor in any other switch mode than floor only?

I just checked my truck to see what setting I had the fan on while at lunch and it was in the window defrost mode. So, I guess I was running the AC and that's why it was sounding like that. Okay, at least my compressor is working. Again, probably explains why I was getting such lousy gas mileage my first week of owning the truck.

Thanks for all of your input.

You can put a switch inline with one of the wires (Purple I think?) that when you shut the witch off (breaks contact) the AC pumps shuts off too. Search around the forum, i think its something like the G and M ac mod or something like that.

Just to clear it up, it the AC clutch that makes the noise, not the idler pully, not the compressor, not the fan clutch. All those other things are silent (unless broken)

Got it. Thanks.

and there are three positions that dont cycle the clutch, off, vent, and floor.

i have a switch in mine.....

its turns the compressor over a couple times to keep it oiled so it doesnt sieze up when you go to turn it on for the summer if you left it off the whole winter the grease and oil in it would drain to the bottom and it would lock up when you turn it on,