I was thinking of a way to use touchscreen with proper controls electronics connected to it for the HVAC controls. Since so many people have had issues with the HVAC units it would be great to have a modern interpretation using touchscreen to control HVAC as well. Does anyone have any good ideas on where to start and how this could be implemented?

 

As others have found there are many complexities in doing any updating of the stock HVAC. Building a custom interface on a touch screen that doesn't look "amateur" or have major usability issues is also much harder than almost anyone expects. Yet this is certainly still the easy part of this. The existing HVAC form factor is not large enough for a screen to do this without major compromises (so you'd need a console 'land grab'). If you created such a screen and controls you'd still need an interface back to the analog world of the original HVAC. This is also more complex than most expect. Many of the reliability issues in the current HVAC are related to the vacuum actuator system & mixing flap control motor but replacing that would be extremely complex - so likely you still have those issues in a hybrid system. Personally I have (and have had) vehicles with touch screen HVAC systems - and I dislike all of them. It is OK for displaying airflow status, temperature and controls for infrequently used items (defrosts, defog etc) - though overall I still can't say I particularly prefer that. For fan speed, temperature and airflow control (and seat and steering wheel heating) I much prefer physical ***** (switches) I can use easily without needing to look at them.

Sometimes "just like a modern vehicle" is not really actually an improvement. Could it be done? Yes. But it would be a few orders of magnitude harder than anyone expected to do it well. It would also probably look quite out of place in a 928 even if it was done very very well. Sorry its not a very positive response - but this is a phenomenally hard thing to do - and then we have to consider if the end result is really what we'd want?

Alan

 

And there’s not enough space to arrange the seats that way

I’ve often wondered if a harness could bring all the various controller connectors back to a single central programmable controller to replace the HVAC, cruise control, bulb test, central locking etc. It would need to handle mostly analogue input/outputs but could have some smart features.
It would be an interesting project for fun, and maybe applicable to any car using the VDO components.
I’m not volunteering though.

 

Audi Tech Defined: MMI (Multi Media Interface)

 

Yes its very flashy (and indeed looks good!), they have tried very hard and implemented a lot - but I still don't find it particularly appealing for a 928 (or really at all from a usability perspective). In a new car it's basically inevitable these days, it allows lower costs and more integrated features and similarity between disparate vehicles mainly based on software adaptations (so very good for the manufacturers).

Assuming you are thinking maybe you can just lift this finished solution - It almost certainly relies on a modern communications bus interface to the vehicle and electrically operated actuators, valves, PWM drivers & closed loop sensors. Not exactly compatible with the individual electrics, mechanics & vacuum controls of the 70's vintage 928 HVAC. It also looks pretty definite its just too wide to fit in our consoles! If your HVAC looked this good you'd certainly need at least a media screen to match...?

Generally I think an updated HVAC for a 928 would better leverage a mainstream German system (VW, Audi, etc) from the late 90's or early '00's that is still basically compatible with something like what exists in a 928. It would still need major adaptations but could provide updated rotary controls and better consolidation (integrate AC switch, rear defroster, seat heating) without needing to throw everything else away. Others have tried this approach and even that is very very hard - even to make a one off for a single car (Vs. a generic solution across years).

Alan