TRY THIS STUFF FIRST!
After some diag I got the A/C to blow out the front vents. There are million threads on this issue half of them are never figured out. This is the second time I have come across this problem so will make this really informative for those who have this problem. If you A/C blows to defrost, yes most of the time its going to be a vacuum leak issue. Step 1) turnkey on engine off, stand by passenger fender and listen.. can you hear the pump running? If it is your pump insn’t dead. Step 2) does the pump run for 30 seconds then shut off? GOOD! You may not have a vacuum leak. If keep’s running for ever you have a leak. Inspect all lines, especially those going down to the hubs for cracks. Also inspect vacuum lines under passenger glovebox. Step 3) can’t find a leak? Disconnect the line going to the ESOF solenoid and plug it, if you pump stops running then your ESOF solenoid has an internal leak. That was my problem 6 months ago, replaced ESOF, A/C blows normally.

TRY THIS SECOND!
So my AC isn't blowing through my front vents again.... (more diag)

AC not blowing through vents and can’t find a vacuum leak? Take off glove box door, turn AC control switch to floor/defrost/front vents, watch the metal arm connected to the side of the big black box move up and down into various positions. I noticed on mine the arm will go down in positions (floor or defrost) But it will not move up! Which needs to happen to switch to front vents. If I push the rod up by hand manually, the ac will blow through front vents, and stay blowing through front vents even after I let go.
PIC of metal arm thing connected to diaphragm, which changes air flow by moving flap inside the big black box:




I am guessing the Diaphragm is the issue? The truck will continue to blow from the front vents even when the truck is shut off and restarted, it will stop when I switch the ac to a different position, it will not return back to front vents.

 

Good to know information that I had not read on here before. Do you plan to take pictures and notes for all of us when you replace the required parts?

 

Thanks for the info. This is the first non-ESOF "defrost only" issue I've seen. Reps sent.

If you are getting the defrost only issue it is a good idea to look into it immediately. I've been through three vacuum leaks (All @!#$% ESOF) and the third one I let go for a bit before tackling. The vacuum pump is not designed for continuous operation and it got fried. That was a $200 mistake. You can get an OEM on-line a little cheaper (+ shipping) but I was going camping that weekend and it would not have been a good weekend in the desert at 90+ degrees with only defrost cooling the cab.

 

Great info and THANKS for sharing! Our Excursion just started doing this. Blows out the defrost for about 15-20 seconds on start-up and then slowly starts blowing out the front vents like it should. ESOF all good on mine. Pump stops running after about 30-45 secs.

Reps your way.

 

i have never seen one of those diaphragms go bad before, but there is a first for everything.
99.9% of the time when i see defrosters only it is due to a cracked or disconnected vacuum line.
i don't know about ESOF because i refuse to own a vehicle with it.

 

subscribing

 

So, mine ended up being the line to the Max A/C assist getting knocked off the last time I worked on the electrical issues with the alternator. It was a leak the pump was able to overcome after about 20-30 seconds, and the vacuum system would then redirect from the defrost back to the vents where it should have been. It could maintain the vacuum (with the pump running way too much), but as soon as the truck was turned off, it would revert back to defrost until vacuum built back up.

So, my scenario fits Tom's experience. However, I have had no problems with my ESOF, because I maintain it properly and keep it in working order.

 

I gave up after three ESOF failures and capped them off. Even with proper maintenance and OEM parts it still hated me. I sunk too much Christmas money over the years into it and finally conceded to manual hub operations from here on out.

I've also had my rubber caps on the vacuum lines get old and crack too letting air in. It's always nice to dive into troubleshooting to find out it's a $3 fix. I wish it happened more!

 

I’m back, I decided to put a 11” inch lift, 40’s, traction bars, cross over steering, mile marker hubs on my truck, and ignored my vent problem. Today I removed all 4x4 air lines, I took out the 4x4 solenoid, and pluged the ac vacuum line directly to the reservoir where the 4x4 solienoid air line use to plug in. I can now eliminated the 4x4 system as a culprit. Pulled the air line out of the reservoir to where the pump’s line is the only line connected to it. I plugged the other line coming out of reservoir, pump still won’t shut off. I am guessing I need to buy a new reservoir before trouble shooting any further. Will report back.

 

Yes I am now determined to figure out this BS problem.

 

i chased a bad vacuum line for 5 months on my 04. it ended up being the tree INSIDE the cab. someone with big feet kicked the tree breaking one of the lines off under the carpet directly below the glove box where the line comes through the firewall.

 

I checked that spilter back in the summer, no leaks. Need to buy reservoir first.

 

There was someone recently that had the common "defrost only" feature on their A/C and it turned out to not be a vacuum leak. I cannot remember for sure what the problem was, but this was the only time I remember it not being a vacuum leak.

Dangit, someone help me out with this...

 

Bad blend door in the box IIRC

 

Varro, I have a spare reservoir on the shelf you can have.