Over the Phoenix summer I have noticed and increasing reluctance on the part of my 2004 6.0 Diesel Limited 4x4 to blow air as directed. For example, quite frequently it insists on blowing AC out the defrost or the floor instead of the panel vents. I took this as a personal preference of the truck and tried to display patience, knowing that eventually it would come around to the course of obedience.

However, the other day, the truck went into defrost blowing mode and simply refuses to accept other input, such as vent or floor. I explained to the truck that this was not very nice and that we "work together" on these things, but I must say, it has been absolutely beligerent about staying on defrost.

Sometimes in the past, as a way of protest to my suggestions I suppose, the truck would make a shuddering sound from under the dash which would last 10 seconds or so before it made the switch from defrost to panel.

I must admit, that in general, I have been unfavorably impressed with the AC's performance in the hot Phoenix summer. I did have the AC pressure checked and it is slightly over charged, so no problem there and I am thinking that it is an inner-dashal problem.

I have expressed my dissatisfaction with the AC performance with the truck, but thus far have only been given the silent treatment by it. It refuses to discuss the matter with me period, so I am thinking of taking it to a "group" therapist aka "mechanic". Hopefully they may get through to it and convince it that I do have it's best interests at heart.

Any suggestions?

 

You either have a problem with a leaky vacuum line or the head unit is going out (I assume you have EATC/Electronic Automatic Temperature Control)..

The vacuum pump is on the pass side fenderwell.. You can check to see if it's working.. You can check the lines to your hubs to see if one's been disconnected or cracked.. There are a few lines right behind the glovebox, but they're pretty reliable.. These are the easiest things to look for..

The HU(head unit/digital controls on dash) was not working correctly on mine and the symptoms leading up to it were similar to yours.. It would struggle to move the little door that directed air to the dash or floor.. It made the shuddering noise you descibe.. Then it finally got stuck blowing to the defroster(default)..

EATC can be a PITA to troubleshoot once you know that you are making vacuum and the lines are good.. There is the EATC HU and a vacuum manifold behind it which takes electrical signals from the HU and mechanically switches the vacuum source to actuate the blend and zone doors in the ducting..

You can try to be more forceful, but the electronics like sweet talk.. Even then, they are fickle..

 

Thanks for the info! That at least gives me a place to start looking or to recommend to the mechanic to start looking!

I'll let you know what I come up with.

 

check the switch under the hood. I got $10 that is where your problem lies..

 

Vacuum pump was completely shot. Replaced the pump and AC works great! Also noticed that my breaks seem a lot more touchy too!

Thanks for the info and replies!