Max AC is not Max any more - any ideas?

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It's HOT here in Phoenix these days so I've been using the AC more than usual. My normal routine when getting in a hot truck is to crack the windows and put the AC on "normal" until the cab is about the same temp as outside. Then I roll up the windows and switch to "Max" (re-circulate).

The last couple days I've noticed that when I switch to "Max" the fan makes more noise (as usual) but the air volume coming out of the vents actually goes down (used to go up). It's like I switched it to bi-level or something. I've checked the defroster and floor vents but there's not much air coming out of there so where's all my air flow going?

Any ideas on this one?

Any help would be most appreciated. Did I mention it's HOT here?

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1999 24V, NV4500HD, QC, 4x4, 3. 54, 8' Bed w/ Rhino Lining, 285/75R16s on 16x8 Eagles, Glasstite high topper

 

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Ive got the same problem, seems like a blockage in the duct work,I can't figure it out either,can you blow air back through the vents?or will it damage something?

 

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There is a flapper door in the ductwork that opens to admit outside air or closes to recirculate the air in the cab. You can see it through the glove box opening. You might check to see if it's closing and sealing correctly with the control set to "Max" (my best friend in the summertime!).

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Bill Lins Wharton, TX 98 2500 QC SLT,12 (the CORRECT # of)valves,NV4500,3. 54 LSD,Manik grille guard,Psychotty Air,Amsoil everywhere, Reading aluminum utility body and bumper,Optima yellow tops- silencer ring, cat,& muffler all stolen.

 

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Bill,
Thanks for the input. Because of a similar experience with a F#@d I was looking in the wrong place for the return air duct. After reading your post I went out and discovered the back of the glove box is not covered. Consequently the return air duct sucked a fast-food napkin out of my glove box and blocked the air flow.

CAW440,
If you just open the glove box (you don't have to remove it) and look through the crack on the top-right-hand side you can see a plastic grate with about 3/4" square grating on it. There's a foam-covered flapper behind this grate that's closed when your AC is on normal and opens when on Max to allow inside air to be sucked into the fan. You can also see the vacuum diaphram and arm that moves the flapper. It's on the right-hand side of the grating. While looking through the crack beside the open glove box, you can reach up behind the glove box with your hand and clear away any obstructions. You can also keep an eye on that control arm while you switch from normal to max and see if it's working.

What a simple fix to a simple problem!!!!!

The service advisor at my EX-dealer wanted to schedule an appointment for 5 days from now and keep my truck for 2 more days so he could "have a look at it. " I don't want to get into the whole dealer thing here so I'll post another subject on the conversations I had with the dealers in my area. If you're interested, it's a pretty good story. Especially if you live in the Phoenix area.

Thanks again for you input. You showed me how to solve the problem and I didn't even have to deal with my dealer-phobia.