Inspection Procedure

WARNING: This page is about a different car, the 2004 Lexus ES 330. However, it is still accessible from the selected car via links, so may be relevant.

INSPECT HEATER CONTROL HOUSING SUB-ASSY(TR, SG-5)

Remove A/C amplifier with connector.
Turn ignition switch ON.
Measure voltage between terminals TR and SG-5 of A/C amplifier connector at each temperature.
Voltage:

at 25°C (77°F): 1.8 to 2.2 V

at 40°C (104°F): 1.2 to 1.6 V

Fig 1: Measuring Voltage Between Terminals Tr And Sg-5 Of A/C Amplifier Connector At Each Temperature
Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

HINT: As the temperature increases, the voltage decreases.

Result:

PROBLEM SYMPTOMS TABLE - ROOM TEMPERATURE SENSOR

A	NG
B	OK (when checking from the PROBLEM SYMPTOM TABLE)
C	OK (Checking from the DTC)

B: PROCEED TO NEXT CIRCUIT INSPECTION SHOWN IN PROBLEM SYMPTOMS TABLE

C: CHECK AND REPLACE HEATER CONTROL HOUSING SUB-ASSY (SEE PROBLEM SYMPTOMS TABLE )

A: Go to next step.

INSPECT COOLER (ROOM TEMP. SENSOR) THERMISTOR
1. Remove cooler (room temp. sensor) thermistor.
2. Measure resistance between terminals 1 and 2 of cooler (room temperature sensor) connector at each temperature.
  Standard
  
  Fig 2: Measuring Resistance Between Terminals 1 And 2 Of Cooler (Room Temperature Sensor) Connector At Each Temperature
  Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
  
  Fig 3: Identifying Tester Connection Specified Condition Chart
  Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
NOTE: Even slightly touching the sensor may change the resistance value. Be sure to hold the connector of the sensor.

HINT: As the temperature increases, the resistance decreases (see the chart below).

Fig 4: Identifying Graphic Of Resistance (Room Temperature Sensor Circuit)
Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

NG: REPLACE COOLER (ROOM TEMP. SENSOR) THERMISTOR

OK: Go to next step.
CHECK HARNESS AND CONNECTOR(BETWEEN COOLER (ROOM TEMP. SENSOR) THERMISTOR AND HEATER CONTROL HOUSING SUB-ASSY)
NG: REPAIR OR REPLACE HARNESS OR CONNECTOR

OK: CHECK AND REPLACE HEATER CONTROL HOUSING SUB-ASSY