Custom Automotive HVAC System

Hello To ALL

I’m new to ardunio and this forum. So far I love messing around with the ardunio and the more I do the more my mind goes crazy with possibilities.

A quick background I own a shop that works on restoring and customizing old cars. My personal skill background is in car audio and electrical. I got this from my days working at Circuit City car audio install department. I have done a lot of Audio and Remote Start system installs. From this I have a pretty good understanding of electrical systems in a car. My computer skills are moderate but my programming is very minimal. I am eager to learn and enjoy putting the energy into figuring things out. My bow hunting skills are pretty good too

What I need is just to be pointed in the right direction. I hope this is the right place

The Project:

I have a 1975 Grand Prix I am customizing I want to control all of the electrical components on the car with a central control unit like a cool switch panel and/or a android based tablet. The fist challenge is the HVAC (heater and air conditioning). I have to figure this out in order to finish metal work on the firewall. My plan is to eliminate the original heater box and control due to the fact they use cable to control the flapper doors for Mode (defrost, Vent, etc) Temp, and Air Inlet. I have a donor Vehicle a 1989 Chevy Truck that uses a Digital Heater & A/C control unit and electrical a motors on the flapper doors. I’m going to retrofit the truck HVAC System into the Grand Prix. The truck is my daily driver and I can use it to test and mock up before I finalize the design.

If anyone could give me any insight to help with this project, things I need to learn, or smaller project to put together to help me understand more I would be very appreciative. Maybe someone has done something like this and I can learn from what they did.

I am including a Description of the control system and motors that are in the Chevy Truck, and Wire Diagram. If any Info/Pics are need let me know. Thanks to all that are will to help me make this Grand Prix A cool project. I will update on the progress.

89 chevy Descrip.pdf (97.6 KB)

Door motor Descrip.pdf (53.3 KB)

Your question is too general to give very good answers. If you ask "how do I control the door motors" and provide some essential information like motor type, motor voltage, stall current and type of control (bi-directrional or one way) then we have a question that we can answer. "How do I make this work" is not easily answerable. Best that I can say is to study the examples in the IDE (File menu), check the playground on this site for topics of interest and use Google ("arduino dc motor control" or "arduino temperature sensing").

like any project, break it down into parts.

you have a lot of analog inputs. water temperature, cabin temp, outside air temp, hot wate temp... etc.

learn how to monitor all of those things. get sensors that will withstand your application.

learn about power supplies for Arduinos in vehicles.

once you have some of the basic understanding, you will be able to easily add on motor control. opening a vent or a valve to get a proper mixed air temperature is more about sensor placement than motor movement. a poorly placed sensor can skew the readings and make control impossible. often the cause of endless hours of hardship and loss of hair. not to mention the lost time spent at the bar trying to figure it out.....

some notes on temperature. temperature moves slooooooowlllly.. you open the valve and in a few minutes you start to feel the heat. also, temperature will overshoot. the best you can do is start to back off well in advance of reaching temperature in the cabin.

in all practicality, getting GOOD sensor input is 90% of the problem. control is easy. motors are easy.

the other 90% is the learning curve on learning how to program.

another 90% might be getting your display to work in your dash. fit and function and all that.

and remember the first 90% of the work takes 90% of the time. and that last 10% of the work takes another 90% of the time.

and when you get really stuck, the words of Homer Simpson might help.

alcohol : the cause, and cure of all problems.

Looking at those diagrams, I think you're in the right area. Those door motors look like 12v servos. The potentiometer that it talks about is electrically identical to what's in a model plane servo.

But you don't have the servo's electronics to drive it for you. I think you should look for an Arduino "motor shield" that will have enough H-bridge outputs to drive the number of motors you need. The current should not be very high, but you should measure the DC resistance of your motors to ensure that the stall current will be within the capability of the motor shield. Connect the potentiometer to 5v and an analog input on the Arduino and you should be OK. Try to get one working on the bench first, not in the car.

Do you still have the blower relays? You can't drive them directly from the Arduino without a few extra components like a MOSFET or a relay shield.

Don't attempt to do climate-control, at least in your initial version of the project. That's a surprisingly difficult problem to solve.

Thank you all.

MorganS I think you have a great point. I think I'll start with getting one motor to move correctly on the bench. That will be a good starting point

I do have the blower relays. The whole system is still in the truck and is working. I am not interested in automatic climate control just being able to move the motors turn on the blower on different speeds and turn ac on and off

Basically replace the old control unit.