No T7. Day after charging I went to Iceland for two weeks. Returned with cold that turned badazz on me. Am setting lifetime record for being horizontal. Think few more days in record setting mode and I'll be free. Will do long haul then---am interested to see how long it takes to evacuate 88 or more ambient down to 70 in cabin. That includes monitoring icing in evap.

30 degree evap temps don't do you any good once the evap freezes up.
I have to run my temp on min or 1.

Agreed. Running 23-24 dF at vent is only interesting, not practical. This AC project started as a black death sort out. It turned into an experimental journey to test a few ideas.

Karl, I just read this and the big mo-fo thread about building the system. A/C principles are something I have to concentrate on to get any comprehension ... decidedly non-obvious to me. Happy to now know what hystereris means!

"At the end of the day", so to speak, what ballpark range of system performance improvement did the digital control system yield/enable?. As in, did it make your car's A/C hardware operate more efficiently, allowing the same amount of interior cooling with less compressor engagement time? Or, did it yield cooler temps vs ambient than would have been possible with just the stock controls?

I'm not asking "Was it worth it?" because the learning/develoment experience and the car's ability to keep you comfortable in FLA are obviously two different kettles of fish.

Cheers, John

Hey John… cool that you picked up this old thread.

Digital add to this 911 AC system does 3 things, and does them well. It gathers temp & humidity info from sensors around car and inside evap. It presents that info on a display so monkey in charge can see, in real time, WTFs going on (and learn from it.) Finally, compressor is controlled based on collected sensor info that’s compared to parameters programed in brain (that in this case is an Arduino UNO.) All this is wonderful stuff but doesn’t---in any way---directly improve the cold producing aspect of this AC. Indirectly, it can be said that improvements result from monkey continuing to learn new tricks (from data seen) and refining AC & digital setup along the way. Quantifiable? No. As long as things go in the right direction… is good. (Of course they don’t always do so.)

So why bother?

Digital build began as no more than a glorified thermometer stuck inside evap. When Arduino entered hardware mix, all of a sudden capability to control things was presented. Enthusiasm quickly ensued for dumping capillary thermo sensor/setting module and exploring what would come of Arduino’s use. Key advantage being the flexibility to program an idea, then change that idea/program and do so whenever. Adaptability.

At end of day, digital enables insights to be gained, and, much flexibility to experiment with AC control. Does this matter? It does if one cares about this sort of thing. I do.

Digital layer adds much complexity to AC system. Sensors, wires, junctions, Arduino, display, relays, step-downs… it’s a gaggle of hardware and a build that some surly consider obscene. Being an empirical experimentalist and willing to learn the hard way… this stuff is my opium of choice---I believe you know exactly what’s what. Is a “garage & kitchen” thing. More, there are great people along creations way that are met via such experiments that would otherwise not have been known. In this case, John Lafitte, a.k.a. “Dr. J” joined project to attend sketch/programing (the Arduino.) I enjoyed John’s collaboration start to… well there is no end to this. And John appears committed to this abstract insanity just as I am. Collaborations that work well...the magic of life. Priceless.
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Roger that and thanks for the explanation.. It’s a level or two higher of technical understanding than I possess, and therefore an excellent learning opportunity. I do cringe when I read a 911/930 thread that includes “and then I ripped out the A/C”. Each to his/her own but even up in New England a climate control is required in my book. So it’s a bit like another system I admire, CIS/K-Jet: don’t dismiss it, just understand it, then enjoy it. Just my opinion/view.

Best, John

Welcome John. With all you have going on now with your project, you could set AC thinking aside for a while. And, I turned a mole hill into a mountain---for research purposes. No need for this... 911 AC is qiite capable of putting out cold air without taking my path. When you're approaching AC aspect of project, pow wow time.
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Nice arduino project. Are you using the arduino PID library to control the on/off state of the compressor ? Or is it just if/then logic with some hysteresis ?


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Hey Frank... Thanks. Arduino sketch was created by fellow Pelican "Dr. J" / John. Is if/then logic with a few degrees hystersis. 3 as I recall. Ard connects to low voltage relay that switches 12v side ON/OFF to compressor.
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