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.
Air conditioner Control Module sets DTC B1242 if Evaporator sensor has been detected over 4.9V for 4 seconds.
Item
Detecting Condition
DTC Strategy
Voltage check
Open in signal circuit
Short to battery in signal circuit
Faulty Evaporator sensor
Faulty Air conditioner control Unit
Enable Conditions
IG KEY ON
Threshold value
Evaporator sensor has been detected over 4.9V for 4 seconds
Failsafe
Control with the value of -2?(28.4?)
Temperature(?/?)
Resistance(?)
-10/-14
18
20/68
4.8
0/32
11
30/86
3.3
10/50
7.3
40/104
2.3