I recently had the battery changed on my 2003 suburban and now the air only blows from the defrost. When i start the car up it cycles through the floor board, then the normal "face" vents and then ends up only blowing from the defrost. It does not matter what i change the air flow position to (feet, face, defrost).
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The problem is with a servo that opens & closes the flap that redirects the air. It is located directly above the accelerator pedal (there's 2 identical servos).What happens is when the computer recalibrates the servo to find the min & max servo travel, it puts alot of stress on the gears that control the servo arm when it reaches the min & max of the travel.After repeated calibrations (ie: disconnecting battery) the gear gets pushed away from the toothy portion of the shaft the main gear is connected to, therefore it slips. Becuase the gear slips, the computer cannot determine the min & max travel, so it drops back to the furthest position (where it directs the air to the footwell & defrost).
You can fix this 2 ways.
#1 and probaly most common, replace the servo.
#2, the free way, open up the servo (real easy) & push the gear back into place. Removing & installing the servo is difficult, and requires a small ratchet with a very long arm. Aligning the gearswheninstalling the servo is also difficult. The servo arm has a notch, and the gear has a pin that must go into the notch. Install the servo loosly and get your fingers in there and feel the pin & notch into place. Since the gear's been pushed out once,I guess there'sprobably the possibility of it not lasting as long as new, but its a great way to buy you some time (maybe another 4 years!)
I must say that it almost looks like it was designed to fail.
Thanks for posting, you saved me $$ and time! I had the same problem and thought it was the control module, but when I put in a new module it did nothing. So, I did an internet search and found your posting. Then I went out and removed the servo unit (not the easiest thing to do!), opened it up and found that the main gear was cracked. I returned the control module, bought a new servo and we are back in business! Thanks again.
I have a similar problem, and this looks like it may be the issue but I could use some help. I have a 95 tahoe. My A/c wasn't blowing cold anymore, so a buddy and I attempted to fix this. During the process something happened and as a result, now the vent air only blows out the middle no matter which direction the switch points to (defrost, feet, face, etc) any way the switch isset, the air only blows from the middle area.
Additionally, the small orange lights inside of the buttons (rear defrost, circulate, A/c) don't light up anymore when the button is pushed in for the circulation and a/c. The rear defrost button still lights up orange when the button is pushed in, it's just the other two that don't work.
Both of these issues occured simultaeous. Can anyone offer any insight? Also, if it is the servo, can someone walk me through in more detail how to fix this. I'm pretty green when it comes to fixing these types of things.
on the 95s there's a diode that needs to be replaced on the control head. a dealer will tell you the control head is not serviceable and try to sell you an entire new control head. I went to an electronics shop near me and bought a pack of diodes for $1 (only needed one) and with some desoldering/soldering got mine working again.