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  #1  
Old 07-25-2009, 06:55 PM
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Default A/C blend door motor

Hi guys. I have a 99 Blazer and the door that diverts air across and away from my heater core oscillates open adn closed constantly; even with the air/heater off. If i turn on the A/C, that cold air is blown right across the heater core, except for the few seconds the door closes that path off. Where it the control/motor for this thing? There has to be a way to fix without taking it to a mech. Someone please help.
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Old 07-28-2009, 05:10 PM
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That's for the quick response. I tried the "B+ Rest". I understand that I just disconnect the positive terminal and the systm recalibrates. Either it didn't work, or it takes much longer to calibrate than I am allowing for. Pulled the RDO BAT fuse and followed those directions. Didn't work. The door starts out at max hot. Moves a little toward the cold side, not much, then goes back to max hot. Moves a little further toward the cold side, then back. This continues till it is oscillating from max hot to max cold, spending most of the time on the max hot side. Did I do the steps wrong? Is there something else to try, or am I left with only one option... a highpriced mechanic?
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Old 07-29-2009, 12:51 PM
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You could also try pulling the dash trim so that you can remove the HVAC control module. Once you have the control module unbolted, with the key on, disconnect the wiring harness from the back of the controller. Turn the key off on the truck and walk away for 10-15 minutes. Come back and turn the key back to the ON position (not running) and then plug the module back in. You should hear the temperature actuator move through its positions amongst other things going on. Turn the radio off for this.

I am not sure if the control module needs to be in AUTO mode on each of its settings for this to work, but that is how I have had it set in the past when performing this.
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Old 08-27-2009, 06:55 PM
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The History, Root Causes and Repair of Blend Door Problems

http://www.heatertreater.net/Final%2...fo.htm#History
Click the image to open in full size.
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Old 08-28-2009, 05:19 PM
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Quote:
Originally Posted by Katmandu View Post
The History, Root Causes and Repair of Blend Door Problems

http://www.heatertreater.net/Final%2...fo.htm#History
What you are doing is borderline SPAM. That site has nothing related to the s-series truck. The failure mode and what they recommend for a fix is not related to what goes wrong on these trucks and A LOT of time would be wasted if the advice on that site were to be taken.
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Old 08-30-2009, 08:17 PM
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Originally Posted by swartlkk View Post
What you are doing is borderline SPAM. That site has nothing related to the s-series truck. The failure mode and what they recommend for a fix is not related to what goes wrong on these trucks and A LOT of time would be wasted if the advice on that site were to be taken.
So why isn't there any heat coming out of my Blazer's heater ?????

The heater hoses are BOTH HOT which rules out a clogged heater core, the motor on the blend door operates when the temperature control is turned and the vents operate just fine as well.

And you're saying the blend door is NOT a problem ?

Please tell me what's wrong with my truck's heater and I'll go away.

BTW, I followed the Blend door Recalibration procedure to no avail...

Quote:
Originally Posted by swartlkk View Post
That site has nothing related to the s-series truck.

The failure mode and what they recommend for a fix is not related to what goes wrong on these trucks and A LOT of time would be wasted if the advice on that site were to be taken.
I wrote and asked their opinion as well. For what it's worth, here's their reply.

Quote:
The Chevrolet design is much less susceptible to failure than the Fords and Chryslers, but they are not immune. Two things help the Chevy.

1. The actuator motor has built-in limits and the motor is capable of turning only ~160 degrees. The motor cannot continue to spin and cause an immediate breakage. While the motor moves 160 degrees, the doors only have about 120 degrees of movement, so the motor does apply excessive force after the door closes, but it is limited by the internal motor stops. The door will "bend" but the motor stops before it breaks.

2. Chevy plastic blend doors are better designed and are stronger than Ford or Chrysler. The plastic will still break, but since it's stronger, it takes longer.

The same basic fail mode that we address on other automobiles exists on the Chevy, but because of the motor and plastic, it takes a lot longer to fail and we don't see the same immediate market as the other vehicles. We have prioritized other product development over Chevrolet because the market hasn't really developed yet.

All that said, your '99 could easily be on the leading edge of what will eventually become a common failure. A few things to check:

1. The heater hoses will get hot whether coolant is circulating or not. Try feeling the hoses from a cold start and check that they warm up at about the same rate and get uncomfortably hot at about the same rate as the radiator does. You can always disconnect the heater hoses and flush with a garden hose to be sure. On a vehicle this age, it wouldn't be a bad idea to do a good radiator flush anyway. You'll get better cooling efficiency and clean out the system. Prestone makes a good DIY kit that you can find at Wallmart.

2. You can remove the actuator motor and get to the blend door axle directly. You should be able to turn the door with your fingers and switch between heat and no heat manually. If the door feels spongy or you see cracks in the connector, the door is the problem.

3. We have also seen problems with the re-circ door on the Blazer and it has the same electronic control as the blend door. If this is broken or leaking, it will allow external air into the system and can significantly affect heating efficiency, but won't kill heat completely. Check FAQ #2 for some simple diagnostics for the re-circ door. It's written for the Jeep GC, but the operation is the same on your Blazer.


The heater system is fairly simple. If air is blowing out of the fan, the heater core is hot, and the blend door is directing air through the core...you have heat. It has to be one of those three elements that is causing any problem.

We would greatly appreciate any feedback on what you find and of course, digital photos are gold to us. We are in the mode of assessing the Chevy market and any information would be great.
BTW, I am in NO WAY affiliated with that website, nor am I promoting that website. I'm strictly sharing information on the issue at hand.
  #8  
Old 08-31-2009, 07:57 AM
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The door itself is not the problem. The gear inside the actuator is. kiwiblazer had a post with pictures showing the gear. This is by far the most common failure.
Old 08-31-2009, 07:57 AM
 
 
 
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1974, 95, 99, ac, access, air, blazer, blend, blender, chevy, door, doors, heater, located, location, motor


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