Fujitsu AB F18LAT Series Service Instruction page 38

Trouble shooting 4
INDOOR UNIT Error Method:
INDOOR UNIT
Indoor Heat Exchanger Temperature
Sensor Error
Detective Actuators:
Indoor Unit Controller PCB Circuit
Heat Exchanger Temperature Thermistor
Forecast of Cause :
1. Connector connection failure 2.Thermistor failure 3. Controller PCB failure
Check Point 1 : Check connection of Connector
Check if connector is removed.
Check erroneous connection.
Check if thermistor cable is open.
>>Upon correcting the removed connector or mis-wiring, reset the power.
OK OK
Check Point 2 : Remove connector and check Thermistor resistance value Check Point 2 :
Thermistor Characteristics (Approx. value)
Temperature
Resistance Value (k )
Temperature
Resistance Value (k )
If Thermistor is either open or shorted, replace it and reset the power.
OK
Check Point 3 : Check voltage of Controller PCB (DC5.0V)
Make sure circuit diagram of indoor unit and check terminal voltage at Thermistor (DC5.0V)
1 2 1 2
1 2
1 2 1 2
CN5 CN7 CN8
If the voltage does not appear, replace Controller PCB.
Indicate or Display:
Outdoor Unit : No indication
ERROR CODE : E : 04
Detective details:
When Heat Exchanger Temperature Thermistor open or short-circuit is
detected at power ON.
0°C 5°C 10°C
176 134 103
40°C 45°C 50°C
25.6 20.8 17.1
THERMISTOR
(PIPE TEMP.)
THERMISTOR
(ROOM TEMP.)
15°C 20°C 25°C
80.3 62.9 49.7
02-07
30°C 35°C
39.6 31.7