[Ol'Jim]

I wanted to post an update to this thread. The original "fix" was to replace the cabin air filter. I bought the truck used, and didn't know it had one, until that problem came up a few years ago. It has a pair of filters in there, and they were dirty. Replaced them, and it was fine. Changed 'em yearly after that. Well, it recently started a very similar problem. About every 30 seconds, I could hear the "recirculate" air inlet open up, then close after about 5 seconds. (Any vehicle always gets a louder noise in recirc mode, as you hear it sucking in air from down under the glove box). So I changed the cabin filters again, (not too dirty), and it is still doing this. Normal for 30 sec, recirc for 5 sec, back to normal for 30 sec, repeating consistently. I switched it from floor/heat mode to dash vent/AC mode, hit the recirc button, to manually put it in recirculate. After a minute, I went back to normal floor vent/heat, and it is again doing the cycling of the air inlet. Any ideas would be appreciated. Or some guidance as to where that gate is located, and is there any way to lock it in fresh air mode? Thanks.