Replacing Manual A/c Control Unit

Misawan · October 3, 2007

I have a 2004 Z71 that didn't come with the automatic temp control with the A/C, heater control unit. I need to replace mine and I found one that is the upgrade to the one I have that has the ATC. Does anyone know if this is the only part needed to make this work or will this only work with a truck that originally came with it? I'd like to upgrade if possible.

m0ntecarloss · October 6, 2007

I have a 2004 Z71 that didn't come with the automatic temp control with the A/C, heater control unit. I need to replace mine and I found one that is the upgrade to the one I have that has the ATC. Does anyone know if this is the only part needed to make this work or will this only work with a truck that originally came with it? I'd like to upgrade if possible.

Before anyone responds with the typical negative post on this question I'd like to chime in with some useful information. I have posted this on several forums so far and none of the members on the forums appear to have any useful information or thoughts. I was curious about this as well when I purchased my truck and was sure it would be possible. It's been asked a million times and every response says its not.... I disagree. Here's the post (sorry I write a lot its what happens when you have bad control of the english language hehe.)

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This is just me rambling on here trying to get all my info and thoughts together so bare with me

I have searched the net for info on this and have yet to see any useful info other than 'it cant be done' and 'you should get a new truck that came with it' kind of posts....Oh yea I forgot the classic 'auto controls are stupid why would you want to do that'

I'm curious for those that have looked into this what it is that is so complicated about the swap?

From my research thus far everything points to it being a little tedious but doable swap. I subscribed to alldatadiy for my '03 1500HD which shows all the diagrams/connectors/pinouts for both manual and electronic controls and here is what I have found...(note that I have not physically looked at anything yet)

The electronic controller has two connectors - one is the same as the manual controller connector so that will plug right in. However, the manual control has wires which go to the old school style resistor packs to control the fan speed. These are not used by the electronic controller. The electronic controller uses a single wire (non-existing in the plug for the manual controller) that will control the speed of the fan via PWM. This is the reason the fan won't work when you plug it in. So for the swap you need to add a new wire to connector and get a blower control module ($81 gmpartsdirect)

From memory, all the hardware is the same - actuators, blower motor, etc... Just need the blower control module...

The other new connector on the electronic unit is for the sensors. This guy has inputs for the ambient outside temp sensor, in-car temp sensor, 4 duct temp sensors, and the sunload sensors (pass and driver). You should already have the ambient sensor and sunload sensor. The connector for the sunload sensor may not have pins for the driver/pass sunload (only the light sensor for the headlights.) The 5 remaining temp sensors are all the same part although the housings may be different, haven't figured that out yet. They are $3.98 a piece from gmpartsdirect so my thoughts are its just the sensor not the housing, I dunno... So adding these to the vehicle and running the wiring is the tedious part, but so is tearing your interior apart to do car stereos and people somehow manage to do that all the time...

For those concerned about the BCM, there is only one wire coming from it that tells the unit to turn on and the manual controls have this same wire....

So now we've covered what this unit needs in order to operate correctly. The other issue I have seen people try to scare others off with is the wiring harness. Stating that it costs like $700 from GM. Well I don't know about that but its easy enough to make one....

The info from alldatadiy shows connectors and pinouts for each sensor and control unit. The blower control module connector, temp sensors, and sunload sensor can be purchased from www.mouser.com for somewhere between $.50 to $1 a piece, you will need the appropriate pins and such to go with it but still not terribly expensive. The remaining connector for the dash control unit (this is the guy all the sensors are connected to) I have not yet located, but I spent about 5 minutes last night so who knows.

I should also note that rockauto.com has quite a few pigtail connectors for things like the temp sensor and such if you're lazy and have some extra cash (they are a little on the pricey side.)

So that's where I am at. I'm sure I left some things out but I still haven't seen anything that says this is impossible, difficult or even expensive. I still gotta take things out and have a look in my vehicle. Curious about how those duct sensors are gonna go in, as in am I gonna have to drill into the duct work or what.

Need to get me a used electronic control unit and blower control module first

m0ntecarloss · October 6, 2007

Those thinking about saying its not possible or not worth it read the above post (i know its a lot of words but seriously....) If you think it isn't state why - hopefully its not 'someone told me it wasnt'

Also, try to keep it to useful information maybe? This could end up a good how to at some point. Your opinion of automatic temp controls are totally irrelevant.... As is your opinion of whether or not its worth doing. What matters to one person does not matter to another, who cares...

m0ntecarloss · October 20, 2007

Lots of helpful posts here So anyway, rather than retyping everything silveradoss.com has my posts on this subject and all that really needs to be said here is it is completely and totally doable. Buying BRAND NEW parts for everything it will still be under $300 when I am finished.

At my current phase I have the new auto head unit installed, controlling the blower motor, temp door, mode door, ac compressor, rear window defrost without issue.

Its actually not a difficult job.... Ok that is all.

GatorFan · October 20, 2007

I just wanted to add my $.02. It seems that you have done extensive research into this and I am glad to see you are making progress. I really think that anything is possible if you have the patience and time (well, research does help too). I bet that since you have posted this more people will try. I remember when I changed to LEDs in my manual HVAC controller I had to do extensive research and actually found the info when someone posted how they did it. When I used their advice (and instructions) I was able to pull it off. It was tedious but accomplished.

I say good job on posting your findings and doing all the research. Post your completed project when you are done so we can see it in action. That way you can say, "I TOLD YOU SO!"

m0ntecarloss · October 20, 2007

Thanks for the words of encouragement. I really appreciate it. Right now I essentially have a manual control setup with the automatic unit - just need to add my sensors so the thing knows what to do when I set it to a temp : )

rt4x4 · November 6, 2007

please tell us what all you did plus pictures

FREAKENHYE · November 6, 2007

Cant be done.

I had to say it but yes i like to do jobs that people say it cant be done. I thank you for the information. And who ever says something cant be done just doesnt want to try it or got the wrong information.

m0ntecarloss · November 6, 2007

please tell us what all you did plus pictures

Hey bro, didn't forget about you guys I have not spent much time lately on this swap but will be shortly. I have a problem where my projects interfere with my other projects... I can tell you that right now I am operating without sensors which means its either all heat or no heat - BUT the important part is the blower motor is controlled perfectly. The other neat thing is if I put it on auto when the truck is cold, the blower motor speed only increases as the coolant temp increases - what that means is that it seems to be communicating with the BCM no prob (otherwise it wouldn't know when to turn the fan up...)

Cant be done.

I had to say it but yes i like to do jobs that people say it cant be done. I thank you for the information. And who ever says something cant be done just doesnt want to try it or got the wrong information.

Thanks bro, the surprising part to me is I still can't see where its even that challenging a project. For instance - to supply power and ground to the 'new' blower control module I was able to pull the pins out of the 'resistor' connector used by the manual controller and plug them right into my new controller... Even the pins were the same!

m0ntecarloss · November 6, 2007

Just out of curiousity (and I should probably start a new post for this) - does anyone happen to have their top dash pad off? Or pictures of a truck with it off? This is of course for trucks that DO HAVE the automatic temp control...

I am trying to determine where I need to drill holes and mount the sensors in the upper ducts - I can make a good guess but the factory location would be sweet

Also wanting to know if the sun sensor in your dash has 2 wires or 4...

m0ntecarloss · November 8, 2007

Ok, as promised I started an info site on whats involved. I have A LOT to add yet but figured it'd be nice for those of you who are at work, bored, and need something to do besides what you are supposed to be doing and stuff..... I may try to put this into a forum post but honestly I find it really annoying - wiki's are so much easier/faster for this kind of thing

Anyway, if you can handle my smartass/sarcasm here you go:

http://montecarlo.homedns.org:8080/wiki/in...erado_Auto_HVAC

HotRodV6 · November 29, 2007

man just the other day i was thinking i wish my truck had the auto a/c, my old car a 2K Olds Bravda had it and i loved it.

Thanks for doing all the research and such, and this will def be something im gonna do in the future. Im also going to add the steering wheel controls and an SS guage cluster, got any info about that??

m0ntecarloss · November 30, 2007

Thanks for doing all the research and such, and this will def be something im gonna do in the future. Im also going to add the steering wheel controls and an SS guage cluster, got any info about that??

Hey bro, don't have any info yet but the steering wheel controls are next on my list. There's tons of info about that in all the different message boards but would be nice if it was consolidated at least into one location... I am still debating whether to buy a steering wheel and go through all that or save a bunch of money and just wire 4 push buttons into the BCM.... Not sure where I'd locate them yet though if I did that....

I apologize for complete lack of updates on the auto temp thing - I have been driving for like a month+ now with no control over temp (either full heat or full cold), surprisingly it hasn't bothered me that much considering its like the complete opposite of 'auto' right now hehe. It helps I can control fan speed and where the heat comes out of...

HotRodV6 · November 30, 2007

would you mind posting up the part numbers of all the connectors and pins you ordered, as well as the part number for the blower control module, on my 03 one of the temp slider lights is burned out, and ive heard its hard to replace the bulb, so im just going to start gathering parts and do this swap to the auto setup.

Thanks