There are vehicles that the HVAC control is no longer available or cost prohibitive. Most of them work very similar. I am interested in developing a control unit that could be universal with different variations.
I have knowledge of how they work and can make a list of requirements that would include reading 1 to 5 thermistors, servo or stepper motor control, PWM blower control and can bus.
From reading similar post on here it is misunderstood that the sensors, motors and controllers are all in place. They need a controller that is otherwise unavailable or $1000 for a 20 year old used one with the same problem as the one being replaced.
Please read and use the topic "How to get the best out of this forum."
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I suggest you do some research into the environment your project will be installed in. You will find it is one of the worst environments for electronics, and normal designs may work they will probably not survive especially when you get lots of them out there. Look at this link for a start: There is a good app note AN2689 by ST on automotive electronics. reading it will help you a lot.https://www.st.com/resource/en/application_note/cd00181783-protection-of-automotive-electronics-from-electrical-hazards-guidelines-for-design-and-component-selection-stmicroelectronics.pdf
Also take a look at this: Distilled Automotive Electronics Design | Analog Devices This will get you started in the path of automotive elctronics. You will also need to validate how they control various parts such as cabin air flow.
I do automotive repair. I diagnose vehicles with 50 modules on 6 networks but the service information makes sense. I know how the sensors work and what I am interested in is only the controller that would be in the passenger compartment. All of the sensors and controlled devices are OEM from the vehicle manufacturers. I just need a touch screen that can for example increase fan speed at a temperature threshold by increasing the duty cycle.
I could do it easy if I could make any sense out of this arduino software and the random layout.
I looked at that but what you are thinking is not what I am interested in doing. For instance the device I would be controlling already has a diode built into it. The relay that supplies power to it is activated at key on. It only has to supply PWM and read the position. It would activate a relay that is already there and already protected because the controller that is unavailable needed and did the same thing. There just are no new ones and a very nice vehicle has no climate control because of that.
That is great, and with that background you know you are describing a multitude of possible vehicles that have different controllers and communications busses. We both know the logic for the HVAC (Heating Ventilation Air Conditioning) was distributed to several different locations depending on make and model.
Having been around these for many years from your description I do not have a clue as to what your "controller" needs to do. From my memory the PWM generally would control the fan speed, a heavy duty switch or relay would be required for the compressor clutch. When they tried PWM on the clutch the clutch would not last.
Generally a message would be sent to the ECM (Engine Control Module) that an additional load is being applied which in turn would increase the engine speed. This message could come from the CCU (Climate Control Unit) but there are other sources depending on the vehicle. The ECM could send a signal to the CCU to back down a heavy load is being placed on the engine such as fast acceleration.
The sensors (they are not all the same) could be measuring ambient in the cabin, engine compartment, atmosphere, return and delivery air through the heat exchanger. Then there is the safety's on the refrigeration unit and associated hardware. There is a lot more going on, again it is make and model dependent. I would like to help but I do not have the hours free to make a guesstimate and or solve this project.
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