Prostar ac

[DosGatos]

Changed the arduino set up on my truck. Put a capillary tube thermostat on the evaporator.
thermostat
Also added a setpoint controller for the evaporator while everything was opened up. It could be used instead of the thermostat and is field adjustable. Right now it's a handy temp probe for the evaporator and controls nothing.
Setpoint Controller
side note found the thermistors on amazon for about $12ea but not going that route today.
Calibrated the thermostat in an alcohol ice bath.
Then rewrote the arduino to simulate a trinary switch. Couldn't find the right trinary. Found a binary for the low/high safety but would have had to add a separate switch for the fan. Spent too much time trying to find the parts to add another switch port to the high side so...

/*
DosGatos trinary switch emulator
pressure transducer psi reference voltages taken with gauges attached
45 - 0.67
150 - 1.55
325 - 3.10
360 - 3.40
NOTE: Evaporator temp is monitored by separate capillary tube thermostat wired in series with compressor relay
*/

void setup()
{
//Setup IO pins...
pinMode(A0, INPUT); //pressure transducer
pinMode(8, OUTPUT); //compressor
pinMode(9, OUTPUT); //fan clutch
pinMode(2, OUTPUT); //error led
//set initial state.
digitalWrite(8, HIGH);
digitalWrite(9, HIGH);
digitalWrite(2, LOW);
delay (3000);
}

void loop(){
delay(2000);
int sensorValue = analogRead(A0);
float volt = sensorValue * (5.0 / 1024.0);
if (volt < 0.67) {digitalWrite(2, HIGH);//system low pressure, illuminate error light (led)
for(;;){};//infinite loop of nothingness
}
if (volt > 0.67 && volt < 3.40) digitalWrite(8, LOW);// pressure in range, run compressor
if (volt > 3.30) digitalWrite(8, HIGH);//system pressure too high, shut off compressor
if (volt > 3.10) digitalWrite(9, LOW);//run fan to cool condenser
if (volt < 1.60) digitalWrite(9, HIGH);//condenser cooled, turn off fan
/* the volt values need to be adjusted after seeing the system run with gauges and temp probes to get the right response. */
}

No schematic offered.
Ran the system with gauges and a temp probe in the vent. Compressor shuts off when the evaporator gets cold, fan runs as needed to cool down the condenser. Most of the time the evaporator temp shuts off the compressor before the fan threshold. 85 degree day and vent air is 48-50.
As good as it ever got with the factory controls.