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A/C switches to Heater & Defroster vents
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woody45
Novice
Jun 18, 2017, 11:43 AM
Post #1 of 11
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A/C switches to Heater & Defroster vents
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2007 Chevy Tahoe LTZ
5.3 l Flex fuel
185,000 miles
Intermittently the A/C will switch to the heater & defroster vents (still cold). The only way to get it to switch back is to turn the key off and restart the engine. Then it's fine till the next time could be days or weeks or hours. It's either control,actuator or update program. Any tech had this problem on 2007 or newer truck, Tahoe or suburban
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Hammer Time
Ultimate Carjunky
/ Moderator
Jun 18, 2017, 12:06 PM
Post #2 of 11
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Re: A/C switches to Heater & Defroster vents
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What you need to do is scan the AC module for stored codes. You will need an enhanced scan tool to do this.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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woody45
Novice
Jun 18, 2017, 5:28 PM
Post #3 of 11
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Re: A/C switches to Heater & Defroster vents
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I have a Tech2 which scans all the modules there are no codes in any of the modules. I'm actually a retired tech. I've done the mode door relearn and checked it's operation of course it's working normal when I can check it. There may have been an update don't know or maybe a mode door actuator issue. Trying to figure it out before replacing any parts thanks for the reply.
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Hammer Time
Ultimate Carjunky
/ Moderator
Jun 18, 2017, 5:33 PM
Post #4 of 11
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Re: A/C switches to Heater & Defroster vents
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A mode actuator isn't going to move on it's own without a power supply so unless the door itself is broken, I think you can rule that out. My money would be on the control head, especially since it's not recording any of this malfunction.
I don't think the mode doors do any calibration. Just the blend doors.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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woody45
Novice
Jun 18, 2017, 7:43 PM
Post #5 of 11
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Re: A/C switches to Heater & Defroster vents
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I know all the actuators on the newer automatic systems have a feed back circuit that tells the control module where it is compared to where the module is telling it to go. I know some of the systems would go nuts with the wrong signals. I was hoping someone would have had this experience with a 10 year old Tahoe.
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Hammer Time
Ultimate Carjunky
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Jun 18, 2017, 7:52 PM
Post #6 of 11
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Re: A/C switches to Heater & Defroster vents
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It wouldn't matter if we had. No 2 issues will be the same. You're going to have to troubleshoot the system.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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woody45
Novice
Jun 18, 2017, 8:11 PM
Post #7 of 11
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Re: A/C switches to Heater & Defroster vents
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Very intermittent problems are almost impossible to diagnose unless you can actually have them act up when you are connected. Over 40 years as a new car technician I can tell you that usually if you have a problem with a 2007 Tahoe it's not going to be the only one. As with every other problem I've had there are countless other Tahoes with this issue I was hoping someone on this forum would have run into it. But thanks for your input.
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Hammer Time
Ultimate Carjunky
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Jun 18, 2017, 8:19 PM
Post #8 of 11
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Re: A/C switches to Heater & Defroster vents
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That may be the way dealer techs work but the rest of us in the Independent world don't rely on pattern failures to diagnose a problem.
I've already checked for TSB's so it looks like you are going to have to resort to actual diagnosis.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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woody45
Novice
Jun 19, 2017, 7:06 AM
Post #9 of 11
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Re: A/C switches to Heater & Defroster vents
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Sorry I bothered you. As I said it only acts once in a while never when I can attempt to diag the problem. I was hoping someone on this site may have run into this problem.
Again thanks for your time.
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Discretesignals
Ultimate Carjunky
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Jun 20, 2017, 9:02 AM
Post #10 of 11
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Re: A/C switches to Heater & Defroster vents
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If it is really intermittent, maybe you should go ahead and check the current calibration in the HVAC module and then go and see if there are any updates available. If there are, go ahead and reflash and see if that issue is resolved. Maybe a later calibration will have better diagnostics in the programming.
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
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woody45
Novice
Jun 20, 2017, 9:10 AM
Post #11 of 11
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Re: A/C switches to Heater & Defroster vents
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Thanks I'll check in to module updates, appreciate your help.
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