B1412

HEATING / AIR CONDITIONING: AIR CONDITIONING SYSTEM: B1412/12: Ambient Temperature Sensor Circuit
B1412/12 - Ambient Temperature Sensor Circuit

DESCRIPTION

The thermistor assembly (ambient temperature sensor) is installed in front of the condenser to detect the ambient temperature which is used to control the air conditioner "AUTO" mode. This sensor is connected to the air conditioning amplifier and detects fluctuations in the ambient temperature. This data is used for controlling the cabin temperature. The sensor sends a signal to the air conditioning amplifier. The resistance of the thermistor assembly (ambient temperature sensor) changes in accordance with the ambient temperature. As the temperature decreases, the resistance increases. As the temperature increases, the resistance decreases.

The air conditioning amplifier applies voltage (5 V) to the thermistor assembly (ambient temperature sensor) and reads voltage changes as the resistance of the thermistor assembly (ambient temperature sensor) changes.





WIRING DIAGRAM





INSPECTION PROCEDURE

PROCEDURE

1. READ VALUE USING TECHSTREAM (AMBIENT TEMPERATURE SENSOR)

(a) Connect the Techstream to the DLC3.

(b) Turn the ignition switch to ON.

(c) Turn the Techstream on.

(d) Enter the following menus: Body Electrical / Air Conditioner / Data List / Ambient Temp Sensor.

(e) According to the display on the Techstream, read the Data List.

Air Conditioner





OK:

The display is as specified in the normal condition.

Result





C -- REPLACE AIR CONDITIONING AMPLIFIER Removal

B -- PROCEED TO NEXT CIRCUIT INSPECTION SHOWN IN PROBLEM SYMPTOMS TABLE Problem Symptoms Table
A -- Continue to next step.

2. INSPECT THERMISTOR ASSEMBLY (AMBIENT TEMPERATURE SENSOR)

(a) Remove the thermistor assembly (ambient temperature sensor) Removal.





(b) Measure the resistance according to the value(s) in the table below.

Standard Resistance:





HINT
- Even slightly touching the sensor may change the resistance value. Be sure to hold the connector of the sensor.
- When measuring, the sensor temperature must be the same as the ambient temperature.
- As the temperature increases, the resistance decreases (see the graph).

(c) Reinstall the thermistor assembly (ambient temperature sensor).

NG -- REPLACE THERMISTOR ASSEMBLY (AMBIENT TEMPERATURE SENSOR) Removal
OK -- Continue to next step.

3. CHECK HARNESS AND CONNECTOR (AMBIENT TEMPERATURE SENSOR - AIR CONDITIONING AMPLIFIER)

(a) Disconnect the A18 thermistor assembly (ambient temperature sensor) connector.





(b) Disconnect the H24 air conditioning amplifier connector.

(c) Measure the resistance according to the value(s) in the table below.

Standard Resistance:





(d) Reconnect the air conditioning amplifier connector.

(e) Reconnect the thermistor assembly (ambient temperature sensor) connector.

NG -- REPAIR OR REPLACE HARNESS OR CONNECTOR

OK -- REPLACE AIR CONDITIONING AMPLIFIER Removal