Arduino-Uno

//Pinouts
  int THERM_pin = 3;
  int AC_pin = 9;
  int PWM_pin = 3;
  int CAR_pin = 8;
  int CAR;
  
//Circuit Constants  
  float R2 = 200;
  float A = .001454437;
  float B = .0002335551;
  float C = .0000000872799;
  
//Fan Settings
  float MIN_fan = .15;
  float MAX_fan = 1;
  int MIN_temp = 82;
  int MAX_temp = 92;
  byte FAN_speed = 0;
  
//Calculation Settings
  int ADC_depth = 1023; //This is the default depth of an arduino Uno, different boards may have different depths. 
  int PWM_depth = 255;  //This is the default depth of a PWM driver for an arduino, this may change from board to board. 
  byte FAN_trim = 0;
  byte ALG_trim = 0;     //This is part of the learning algorithm that finds the optimal fan speed for your desired temperature range. 
  float COOLANT_temp;
  float TEMP_prev;
  byte FAN_speed_prev;
  
//DEBUGGING PINS
  int CAR_on = 12;
  int AC_on = 13;
  
void setup() {
  //Set pin modes
    pinMode(AC_pin,INPUT);
    pinMode(CAR_pin,INPUT);
    pinMode(PWM_pin,OUTPUT);
    digitalWrite(CAR_pin,HIGH);
    FAN_speed_prev=128;
  //DEBUGGING
//    Serial.begin(9600);
//    pinMode(CAR_on,OUTPUT);
//    pinMode(AC_on,OUTPUT);
}

double Thermister(int RawADC) {
 double TEMP;
 TEMP = ((1024*R2/RawADC) - R2);
 TEMP = log(TEMP);
 TEMP = 1 / (A + (B + (C * TEMP * TEMP ))* TEMP );
 TEMP = TEMP - 273.15;            // Convert Kelvin to Celcius
 return TEMP;
}
 
   
   
void loop() {
  CAR= digitalRead(CAR_pin);
  digitalWrite(CAR_on,LOW);
  digitalWrite(AC_on,LOW);
  FAN_speed= FAN_speed_prev; 
  if(CAR == 0) {

//  Serial.print("Car is On  ");      //DEBUGGING LINE

    digitalWrite(CAR_on,HIGH);
    COOLANT_temp = Thermister(analogRead(3));
 
//Serial.print(COOLANT_temp);         //DEBUGGING LINE
//Serial.print(" C  ");                //DEBUGGING LINE
    if(COOLANT_temp > MIN_temp) {
           
       if(COOLANT_temp > MAX_temp) {
         FAN_speed=MAX_fan*PWM_depth;
         analogWrite(PWM_pin,FAN_speed);
         delay(1000); }
       else {
           
           if (TEMP_prev < COOLANT_temp) {
              FAN_speed = FAN_speed_prev++;
            }
           else if(TEMP_prev > COOLANT_temp) {
              FAN_speed = FAN_speed_prev--;
            }
           else {
             FAN_speed = FAN_speed_prev;}
        
//Serial.print(FAN_speed-FAN_speed_prev);            //DEBUGGING LINE
//Serial.print(" TRIM  ");                            //

            analogWrite(PWM_pin,FAN_speed);
            
//Serial.print(FAN_speed+ALG_trim);  //DEBUGGING LINE            
//Serial.print(" Speed  ");          //DEBUGGING LINE
              
            TEMP_prev = COOLANT_temp;
            delay(1000);
       }}
       else {
         FAN_speed = MIN_fan*PWM_depth;
         analogWrite(PWM_pin,FAN_speed);
       }}
  else {
  analogWrite(PWM_pin,0); }   
//Serial.print(FAN_speed);          //DEBUGGING LINE
//Serial.println(" bits");          //DEBUGGING LINE
 }