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Re: air flow prob
The linkage that runs the blend door isn't working, these are the doors that control hot and cold and air flow to dash floor ect...they are located in the air box behind the dash ................ you may be able to pull the heater controls out of the dash and spot the problem but it's likely that the problem is in the air box itself and removal of the entire dash is required (big job!!!!!!!!!).........if your vehicle uses vacuum to control this (some gms use vaccum and some a cable)you might have a hose disconnected under the hood by the heater fan.........if it's a cable it may be knocked off at the dash controls or at the other end on the heater box..........sometimes removal of the glove box will give you acess to this connection. hope this helps..........thanks fro choosing FIX YA!
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Mode Door 1. a.This door regulates air flow to either the dash vents or defrost/floor. If you have air flowing only through the vents with no defrost or floor, this door is failing. From our experience, this door is usually the first domino to fail. Not sure why, just is.
<!--[if !supportLists]-->4.Mode Door 2. a.When mode door 1 is set to divert air away from the vents and into the second stage of the system, door #2 chooses whether air goes to the defrost vents to the windshield or out through the floor vents in the passenger and driver's side footwells. Failure is indicated by an inability to choose between defrost and floor. b.This door turns out to be the most difficult to replace. In order to replace the door, the dash panel has to be removed. It's still better than the dealer fix because you don't have to evacuate the AC system, drain the radiator, and remove the plenum box. But it is more work than the other fixes. When this door breaks, it falls in the down position, blocking the floor vents and diverting all air through the defrost vents. From a safety standpoint, this is good since you'd most likely rather have a clear windshield than warm feet. We suspect that a large percentage of customers will just leave this door unrepaired. You will have heat through the dash vents and to the windshield, just nothing to the floor. It's inconvenient, but you'll have to make the determination if warm feet are worth the extra work to fix the door. An extra pair of socks is easier.
This is a common problem on this site. In your case I would look for a vac leak or a sticky blend door. Since the direction of air flow changes when you are accelerating, I'm going to guess the blend door or doors are controlled by engine vacuum. There may be a vac leak between the dash and the engine, or the blend door may not be able to move back and forth correctly. Defrost is the default position when a problem occurs, to make sure the windshield is clear of fog or frost.
Sounds like a wiring problem with the harness behind the dash. You have one or more blend doors that open and close to direct air flow thru the vents. If there is a problem, the default position is defrost for safety. A mechanic would check the blend doors for voltage and operation.
i just went thru this problem with my 95 1500. on mine it was the controls just like you discribe on yours one for fan one for temp and one for settings.first i thought it was the heater blend door acturator. its located on left side of heater next to the gas peddel. pulled the wire plug out and test for power theres 3 wires to this plug one white one brown and one black. the brown wire was hot with key on the black is ground and the white is the one that sends a siginal to this electric motor witch redirects air flow from floor to dash vents to defrost. i had to order the controls thru autozone 135.00 with shipping. you might get lucky and find one at a bone yard the ones in my area dident have any. i almost bet you will find thats your problem too. good luck OLD SCHOOL.