HVAC acting weird!

[denalianyone]

I noticed more times than a few that my HVAC would reset upon turning the ignition off and on within a 5 min span. The display would act as if the battery died showing both the digital driver and passenger temp on.


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[swathdiver]

I'm not sure what you mean. While my display is different, it always shows the temperature setting for each side the way I have it configured.

 

[denalianyone]

It resets. Just say I have it set for 90 for just the driver side. I go to the store and come back the gauge resets to 74 for each side and the AC snowflake is engaged.


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[swathdiver]

All I can think of Ray is that the control head is bad but to know for sure would want to see the codes stored in the BCM or at least watch it operate with a bi-directional scan tool.

 

[denalianyone]

Ok thx, no codes as of yet


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[swathdiver]

Ok thx, no codes as of yet


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How do you know? These kinds of error codes do not set off the light on the dash.

 

[denalianyone]

How would I check for HVAC codes then?


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[R Fos]

Is your memory settings set to the temp it goes to under remote start and then starting. My older shortly Denali does that always has defaulted to memory setting when key in ignition.

 

[swathdiver]

Is your memory settings set to the temp it goes to under remote start and then starting. My older shortly Denali does that always has defaulted to memory setting when key in ignition.

I forgot about this, I never really move mine off 68 except in the summer when I drop it to 66.

You need a scan tool Ray that can check BCM (body) codes. Tech-2.

 

[Doubeleive]

my hvac has 3 settings
1. with the power off I can set the ambient temp for driver/passenger
2. press the auto button then set the temp I want driver/passenger/rear (a/c is auto on I believe as dehumidifier function regardless if you have it set to warm or cool)
3 press the power button and set the temp driver/passenger/rear/or defrost (with passenger disabled), a/c

when I cycle the key it remains wherever I left it last time I turned the key on, even hours or days later.

if yours does not stay where you left it last time you turned the key off then something isn't right, it doesn't change on it's own.

74deg is what it defaults to if you disconnect the battery for instance or unplug the control then plug it back in, so it sounds like yours is loosing the constant power connection when the key is turned off, I don't think a fuse would cause this but it couldn't hurt to check them and your grounds and maybe the plugs behind the control make sure they are all plugged in all the way
if you everything looks good you might have a bad control unit or it failed internally to keep power.

 

[denalianyone]

Well the past couple days the temp hasn’t reset with key on and off no matter the time frame. So it does it sporadically


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[denalianyone]

74deg is what it defaults to if you disconnect the battery for instance or unplug the control then plug it back in, so it sounds like yours is loosing the constant power connection when the key is turned off, I don't think a fuse would cause this but it couldn't hurt to check them and your grounds and maybe the plugs behind the control make sure they are all plugged in all the way
if you everything looks good you might have a bad control unit or it failed internally to keep power.

Yup defaulting to 74. I’m gonna pull out the unit and check the connections in the back because I have a lot of wires back there after my double din upgrade install.



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[Doubeleive]

Yup defaulting to 74. I’m gonna pull out the unit and check the connections in the back because I have a lot of wires back there after my double din upgrade install.



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let us know so we can utilize the information in the future

 

[t69chevelle]

Hi, I have been having the exact same issue over the last few years, either the Heat or the A/C is set when the truck is turned off and when restarted the HVAC resets to the 74deg. After replacing the small factory battery with a red Top optima and running a much larger Alternator the HVAC resetting did not happen until the battery started to fail, so I replaced the battery with a different brand AGM and just yesterday it did it again and reset to the 74 deg with the pass also on. Now I am in Southwestern Ontario Canada and we are having the same wicked cold that most of the Mid Western States is having, I believe that it has something to do with the Draw of the starter on the electrical system and the HVAC controls are losing their Memory Power for a split second.
I am looking for a fix that will allow the HVAC to have uninterrupted memory power, has anyone figured this out??? Mine is an 07 Denali and nothing else seems to be affected.

 

[Doubeleive]

Hi, I have been having the exact same issue over the last few years, either the Heat or the A/C is set when the truck is turned off and when restarted the HVAC resets to the 74deg. After replacing the small factory battery with a red Top optima and running a much larger Alternator the HVAC resetting did not happen until the battery started to fail, so I replaced the battery with a different brand AGM and just yesterday it did it again and reset to the 74 deg with the pass also on. Now I am in Southwestern Ontario Canada and we are having the same wicked cold that most of the Mid Western States is having, I believe that it has something to do with the Draw of the starter on the electrical system and the HVAC controls are losing their Memory Power for a split second.
I am looking for a fix that will allow the HVAC to have uninterrupted memory power, has anyone figured this out??? Mine is an 07 Denali and nothing else seems to be affected.

no but you could always go with a bigger battery (more cca's) and/or run 2 battery's like some of us have already, using a block heater wouldn't hurt either.

 

[denalianyone]

Yup my problem continues as well. I have the Big3 and two bs batteries from Autozone. The negative wire was also rerouted to the engine block. I will upgrade to two yellow tops soon.


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[denalianyone]

No more issues after purchasing two XS power batteries to replace my die hard gold’s.


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