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ac/heater stuck on defrost

ac/heater stuck on defrost

Postby neildavis [OP] » Jan 03 2013, 3:55am

i have a 99 sierra and the heater and ac work but only blow out of defrost vents. My first thought was the actuator. After replacing the the part it remains the same. Switch is the next suspect but the lights on the "re-circulation and outside air" lights switches as i move from face vent to defrost vent making me assume switch is good. I've read that a vacuum hose could also be a issue. Any thoughts?. thank you
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Related Topics  2005 Silverado Stuck on Defrost???   Rear defrost   Defrost not working   defrost/heat help   windshield will not defrost   AC won't blow out defrost   Air only blowing out defrost?   Defrost blows debris in cab   truck won't run with ac or defrost on   Air noise from defrost vent   Air noise from defrost vent   Rear Window Defrost stays on 08 Silverado   Aftermarket rear window defrost grid   Rear Defrost / Heated Mirrors and Radio Issues 
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Re: ac/heater stuck on defrost

Postby Critter119 » Jan 03 2013, 5:21am

that is what i suspect, defrost is the default location for the HVAC system to blow out of. you could get lucky and here it if it is in the cab, i believe that there is a group that runs to the back of the switches on the control panel, 1 feed in and several that go to close or open doors as needed, it sound like to feed line is leaking.
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Re: ac/heater stuck on defrost

Postby neildavis [OP] » Jan 03 2013, 2:13pm

Well doesn't that sound fun. Hopefully I it will be close to control panel and not any farther. Thanks
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Re: ac/heater stuck on defrost

Postby neildavis [OP] » Jan 05 2013, 11:10pm

Well found out that there are two actuators. One for temp control and one for mode. I only replaced the temp control. After a frustrating tight space battle with the mode actuator the inside gear had a crack in it. Was able to turn gear enough to leave on face mode till the new actuator is shipped
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Re: ac/heater stuck on defrost

Postby D3Creations » Jan 05 2013, 11:26pm

My 03 is still stuck on defrost. I replaced the mode actuator and is still not working. I'm interested in your results.
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Re: ac/heater stuck on defrost

Postby neildavis [OP] » Jan 06 2013, 12:08am

D3
i know that on my 99 that the 5 prong clip and wires hold a certain volt and amp. Also that my light blue wire is a feedback line that holds 5 volts and a dark blue holds 12. One of the 5 is a feedback line and it is my understanding that if the feedback isn't right that the mode will switch to defrost which is the default. I've also read that on models with the digital temp control that if you pull the hvac fuses while on and insert again it will reset the computer that controls mode. Maybe your need to reset it after replacing the actuator. If not turn the fan on and manually move door to face mode and see if blows. I let actuator hang with connection in and switched controls to test actuator. If it moves you know actuators good. If not maybe be in the wiring. That's what i try but i'm kinda learn as you go.
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Re: ac/heater stuck on defrost

Postby D3Creations » Jan 06 2013, 12:13am

My actuator goes through its cycles but always stops on defrost and starts clicking. My understanding is it needs to be recalibrated, but I have been unsuccessful in my many attempts to do so.
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Re: ac/heater stuck on defrost

Postby neildavis [OP] » Jan 06 2013, 12:39am

my brother cracked mine open and found that one of the gears was cracked and was causing the feedback line to send default. i'm not to sure about re-calibrating it
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ac/heater stuck on defrost

Postby Machster69 » Jan 06 2013, 12:55am

D3Creations wrote:My actuator goes through its cycles but always stops on defrost and starts clicking. My understanding is it needs to be recalibrated, but I have been unsuccessful in my many attempts to do so.

contact Benz604, he has posted the reset/recal procedure here b4
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Re: ac/heater stuck on defrost

Postby D3Creations » Jan 06 2013, 1:09am

Yeah, I tried his instructions several times very carefully. Not sure what's going on.
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