Is it any ac filter for 1999 suburban - 1999 GMC Suburban

There isnt a seperate filter for the a/c air that comes into the truck. There is a cabin air filter that filters incoming outside air, but that wont really help you especially if your using the recirculate option when your a/c is on.
That being said, I have encountered many customers complaining of a mildew smell when first turning on the air conditioning, and in some extreme cases, burning eyes and scratchy throats. The problem is mildew building up in the a/c ducts, which happens when the duct temp. fluctuates, ie, driving for an hour with the a/c on, then shutting off the truck for a couple of hours. I would recommend getting a can of Frigi-Fresh. Its an aerosol can, and you spray it into the fresh air intake. Thats located in the cowl, just below the windshield wipers. Have the truck running, a/c on high, recirculate off, and just spray it into the cowl. It kills all the mildew, mold and bacteria thats growing in the ductwork, and it smells nice. You can substitute Lysol instead, as its pretty much the same thing. Try that and see if that helps.