[rickyrickeric]

Greetings All. Eric here, new to the forum, so I hope I have this in the right category. I just bought a 2003 Trailblazer LTZ, and I love it....except I'm not crazy about the auto climate control. I was researching options, and noticed there are what appears to be two different options for the control panel. This is what is currently in the vehicle:

But then I see these:

So my questions are, what is the difference? Are they interchangeable? Am I correct in that the second unit is manual? Would it allow me to simply turn the different functions on and off at will? I appreciate the help.

 

[chem_man]

Welcome to the Forum!

The top HVAC controller (has the digital temperature readout) is for the automatic HVAC system. The second one with just the temperature sliders is for the manual HVAC system. To the best of my knowledge, they are not interchangeable.

The automatic HVAC controller relies on several different interior temperature sensors to maintain the passenger compartment at the temperature that is dialed into the system. Let's say you set the temperature for 72° F and the controller is set to automatic. If the temperature outside is 92° F, the HVAC controller commands the AC compressor to turn on, and it also commands the HVAC actuators to send most if not all of the air out of the dash vents. Now, if the outside temperature falls to 40° F, the HVAC controller commands that the temperature HVAC actuators to move to allow heated air from the heater core to blend with the cooled air from the AC evaporator to so that the air coming out of the HVAC vents is at a warmer temperature such that the passenger compartment is maintained at 72° F.

Now, with the manual HVAC controller, you have to choose what temperature you want when you want it. You are the one who has to adjust the temperature sliders in order to stay comfortable. Also, you have to manually select if you want only the heater or only want AC.

Now to complicate matters a little more, before the HVAC controller can do it's job (whether automatically or manually), it has to receive the OK for HVAC command from the Body Control Module (BCM). If the BCM does not see the proper HVAC controller present, then it assumes that the HVAC controller is malfunctioning.


Now, I may be wrong in the end and discover that the two controllers are interchangeable, but I doubt it. But, if I am wrong, I will be the first one to admit it.

Good Luck and enjoy your new ride!!!

 

[Diamond193]

Welcome to the forum

 

[metalmike187]

Welcome aboard.

I was going to do something similar with my 2002 LTZ, as it would have been similar to what I had in my 2008 Impala. chem_man is correct that the harnesses are different for the analog style temperature control, versus the digital one. Not to mention the number of sensors connected to the automatic one, as previously mentioned.

You can disable automatic mode and have full control of your current setup, should that be the reason you want to change them.

 

[The Shark]

Yes, as stated above, just don't use auto. Use the air direction button to get it flowing where you want and then adjust to your desired interior temp. By default, the driver side temp selector will do both sides together. This will only change if you adjust the passenger side temp selector independently.

 

[metalmike187]

I went through the process of fixing the ambient air temp sensor to get the numbers to read right as well as the auto HVAC to work properly. Didn't like it. Haven't used the auto HVAC since with no issue whatsoever.