I posted this in the V6 forum because it was a 4.2V6 making the noise, but I guess the more proper place is here. My buddy just got a 4.2L V6 regular cab with less than 20 miles on it (brand spankin' new). He was in my driveway last night showing me the truck (he's a Chevy converter). He loves it - and it's a damn fine truck - but while he had the AC on, it sounded like the compressor was clutching big time to the point that it was making this combo clutch/grind sound almost and it was doing it rather frequently - every 10 seconds or so - maybe even shorter intervals than that. Sound went away when he turned off the AC.

I owned an 02 4.2V6, currently own a Fusion and Explorer, and all of them have distinct sounds when the compressor clutches, but this just sounds BAD. Someone told me that the new F150's are notorious for being low on 134 from the factory? Yet he told me at the same time that the AC system was blowing "cold a** air." Then again, his old Sierra's AC went out at 50,000 miles and GM refused to replace it under warranty, so maybe it's not as cold as it could be? Help - don't know what else to tell him other than take it to the dealership to have it looked over.