The Evaporator sensor located on heater unit detects the core temperature. It is a negative type thermistor whose resistance is inversely proportional to temperature. Evaporator sensor transforms measured temperature into voltage value and delivers it to A/C ECU. when core temperature is blow threshold value, A/C ECU interrupts compressor relay power, in order to prevent evaporator freezing by excessive cooling.
The ECM sets DTC B1242 if there is an open circuit in evaporator sensor signal harness or the measured voltage value of the sensor is more than the threshold value(4.9V)
Item | Detecting Condition | Possible Cause |
DTC Strategy | ● Voltage check | ● Open Circuit in harness ● Faulty Evaporator sensor ● Faulty A/C Control Unit |
Threshold value | ●< 4.9V | |
Detecting time | ● 0.3sec | |
FAIL SAFE | ● Control with the value of -2℃ |
※ Resistance value of evaporator sensor as a function of temperature.
Temperature(℃) | Resistance(㏀) | Temperature(℃) | Resistance(㏀) |
-10/-14 | 43.3 | 20/68 | 12.1 |
0/32 | 27.6 | 30/86 | 8.3 |
10/50 | 18 | 40/104 | 5.8 |
