My 99 EB Expedition has had some strange AC problems from day one. It will get to where it just cools very slowly and the Compressor cycles at idle. It does cool, and given enough time will cool outlet air to the low 40's, but very slowly. Sounds low on gas, right. Dealer checks it, pressure checks it finds no leaks, gas is maybe 1/4 to 1/2 pound low. Works fine now for six to eight months. Again same drill, not low on gas, pressure check, no leaks, but works fine again.This has happened four times since the truck was new. the latest, was this morning, again trip to the dealer, warrantee is now over, as of last month, they pressure checked it again, no leaks, not low on gas, now works great again. I know they didn't do much as they didn't charge me, and the whole thing only took about 10 to fifteen minuets. Though I'm not an AC expert, I do understand the basics of how it works, and for the life of me I can't get a handle on this. It just doesn't follow the rules as I understand them. Any ideas, anyone? Also the system has been completely evacuated twice and refilled.

 

Sounds like you have a VERY VERY slow leak. Back when you had your warranty they should've pumped in a greenish dye with the new refrigerant. It would've eventually leaked out and shown them where the leak was. They obviously didn't want to be bothered and just sent you down the road with a full load of refrigerant. If you plan on keeping the Expy, I'd go to a shop that services A/C systems exclusively and let them find it. They will do the dye test there.

 

They did put the dye in, and have gone over it twice with the black light, once let the AC run long enough to really dump water out of both the front and the rear coils, checking the water with the black light. I still have three years of extended warrantee left on it, so I keep hoping they are putting forth the effort, but you centainly could be right. The dealer has had at least two different techs work on it!!!! I agree it behaves like a very slow leak!!! This particular dealer has a fairly good track record for attacking major problems, at least on a friends F150!!!