Yes the blower controls is just a set of resistors, but that same control also loops back into the compressor to cylce it on and off depending on what the blower motor is set to. I.e. fan on 1 might mean 75*, fan on 4 might mean 60*.
But as far as the evap temp switch goes. You first need to find out what is the lowest
temp that it trips at. And then you will go up from there. If the evap gets down to 40* before it trips the thermostat, then you need a switch that will trip at 40*. Then you would adjust up.
And it all depends on the temp switch. If you have one that outputs at a programed temped then yes. I.e. you set it for 60* and when it hits 60* it outputs a ground(or power). Then you could use that to trip a relay for the thermostat, it would then cut off the ac compressor till the temp with up.
The only thing with doing it that way is you will get a false temp. The evap is much colder then the temp out the vents. So setting it to 60 might mean 70* out the vent. It would take some getting use to and they would have to be an override so the temp doesn't get set to low.
I could probably help with making the wiring. Its just right now I'm replying from my cell so I'm not at home with my diagrams and software.
But just know fan controls are tied into temp on the civcs.
Also explain what all u want from this system. Could be over thinking the whole thing.
If your wanting to hit ac and set temp. Then all you might need is just a digital temp controller and some relays
The ac would be wired up that when it come on the fan spend would be 2 and then you set the temp and it will blow out cold air till that temp relay is triped. Then it could cut the compressor and just blow out air till the temp goes up, then the compressor would kick back on. Migt need a time delay so the compressor wouldn't be cycling on and off to fast.