I just noticed this the other day but didn't investigate it until today.
With the heat/AC controls in any position other than "off" the electric clutch on the compressor cycles on and off with an audible click. Sounds like the semi-fast click of a time bomb in a cartoon. You know, tick, tick, tick at rate that increases to about 1 per second. Actually, it starts slower than that then as a few seconds go by, the rate of engagement/disengagement increases.
If I turn the heat selector to "off" it stops completely. If I turn it to A/C it engages fully for about 18-20 seconds, then starts cycling on and off.
I have no idea if this is normal or not, but I am suspecting not because I think I would have heard it before in all the years I've had the truck.
With the engine off, I can spin the compressor by hand. There is some resistance, about what I guess I'd expect from a compressor. But it certainly doesn't feel bound up or abnormally tight in any way.

I have video of it, I just have to figure out how to attach it or otherwise make it available for you guys to see.

It'd be cool to be able to do whatever I have to do in a leisurely manner instead of having to fix it overnight before a scheduled long trip in the middle of a hot summer.

Any ideas/suggestions?

Thanks!

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It's low on refrigerant. That's all. Also you probably have some wires rigged somewhere. These year models only use the compressor in Max ac, norm ac defrost and mix.
It should never cycle on in vent or floor.

 

Thanks.
I'll get it recharged and see if that does the trick.
I may have been mistaken about it engaging on vent or floor. I was flipping the selector back and forth trying to find which ones made it stop, not necessarily which ones made it cycle. I just know it was doing it on mix because that is where I usually keep it in the winter time.

 

EXTRA INFO
Air Conditioning Troubleshooting and Repair

 

Also check the plug on top of ac unit..... A few years back mine was so loose i could wiggle it and disengage the ac clutch

 

It's a heartbeat!

 

That is an excellent summary of A/c troubleshooting info! Thanks!
I am leaning towards the low refrigerant angle because when I turn it off entirely for a few minutes, then re-engage it, the clutch stays engaged for about 15-20 seconds, than starts to cycle.
To me, that kind of rules out the electrical connection on top. I had wriggled that around, too, with no change in performance.

So I'll make a stop at the garage and get it recharged with refrigerant and see how that goes.