My 99 F150 yesterday started to make a clank noise with the AC on. I’ve heard clicks before on various cars but never a clank. I looked at it this morning and it seems to make the noise when the clutch disengages. Is the clutch going and if it is do I have to pull the compressor to change the clutch out. I have a 5.4 in the truck and the compressor is way down there.

Sounds like it is coming from the front or the hub.

 

The front hub on your compressor may be made of 2 pieces, isolated by rubber "pucks". You can see 3 "*****" on the front hub. The rubber starts to disintegrate, causing the "clank". You're lucky, many folks don't notice the noise until the compressor clutch flies apart.
If so, you need to replace the compressor clutch and pulley. (they wear together and must be replaced as a pair) This can be done without opening the system. A clutch kit, including the clutch coil that doesn't really need to be replaced, is about $80-90.
If your front hub doesn't have the 3 *****, look close for damage or play when wiggling the hub. If there is play, the hub is bad and the info above also applies.
Good Luck

 

The clutch plate may be replaced by itself. The wear on the pulley's face can be accommodated via shims.

Chances are, his clutch plate is separating.

 

It is the type that looks like it has three ***** and nothing feels loose by hand. I did notice that last Sunday it felt like warm air was blowing for about 15 min and then it kicked in cold. Is that the clutch slipping?

Just hit 100K last month and in that month I have replaced 4 ball joints, 4 tie rods and did the brakes. Whats another $90 if it will keep me cool.

 

Yes, it "can" be replaced by itself, but most times both clutch faces have corresponding grooves worn into them. Putting a flat clutch plate against a grooved pulley face severely reduces the contact area. I've seen many instances where the clutch won't hold after only replacing the plate.

 

So if the clutch slips how can I tell? Also what indications would I notice inside the cab?

 

The clutch will be moving noticeably slower than the pulley, possibly not at all. You might see smoke or hear noise. It all depends on how badly the pulley face is grooved.
If the grooves are minor, replacing just the clutch can work, but you won't know until you put it all togeher and try it. Personally, i would just replace both pieces and be done with it.