I have had my F-150 4.2 for about 2 years now and recently I have been noticing a loud clicking sound coming from my engine. I recently put a high flow Specter intake in place of my stock intake and it helped with the clicking sound. I noticed when I opened the hood, and found out that it was my air compressor (or at lest I think it was) making that horrible racket in my engine. It doesn't make a sound when it is off. And I have no idea how long it's been since the last Freon charge, but it still blows cool air on normal A/C and chilly on Max A/C. Now I got to ask, why is it making this sound whenever it's turned on?
If this is the wrong place to post this please let me know

 

watch closely....when it is "clicking"....is the clutch for the A/C engaging and disengaging??
does it go away with A/C turned off?

if so it is a sign the A/C system is needing some attention.

or maybe it is a bad spot on the serpentine belt itself?

look over the vacuum lines.

if it isn't any of those you might be wise to get it checked out, for a bigger gremlin maybe lurking

 

Yes it does go away when I turn it off. I may need a combonation of both a new serpentine belt and some work on the A/C. Even though the truck has been garage kept most of it's life (lest until I got it). So stuff had time to leak and dryrot.