Inspection of HVAC Control Module and Its Circuits

Precautions: Precautions for Diagnosing Trouble · General safety (00)

HVAC control module and its circuits can be checked at HVAC control module wiring connector by measuring voltage.

NOTICE:

If you connect a voltmeter or an ohmmeter directly to the HVAC control module with the HVAC control module connector disconnected, you can damage the HVAC control module.

Never connect a voltmeter or an ohmmeter directly to any terminal on the HVAC control module with the HVAC control module connector disconnected.

Voltage and Signal Check

1)Remove HVAC control module referring to HVAC Control Module Removal and Installation:Automatic Type.

2)Connect “G20” connector.

3)Check voltage and signal at each terminal.

NOTE:

•As each terminal voltage is affected by the battery voltage, check that battery voltage is 11 V or more with ignition “ON”.
•Normal voltage of circuits with asterisk (*1) cannot be measured correctly with voltmeter because they are pulse signals. Check them with oscilloscope.
•Normal voltage of circuits with asterisk (*2) are reference values corresponding to when control sets the temperature control actuator at max cool position, air flow control actuator at “FACE” position, air intake control actuator at “REC” position and battery voltage is approx. 12 V.

[A]:

HVAC control module connector (View: [a])

HVAC control module

“G20” connector

Terminal No.	Wire color	Circuit	Normal voltage	Condition
G20-1	GRN	Output of 5 V power source for actuator position sensors	Approx. 5 V	Ignition: “ON”
G20-5	BRN	Ground for actuator position sensors	0 – 1 V	Ignition: “ON”
G20-6	YEL	Ground for sensors	0 – 1 V	Ignition: “ON”
G20-11	WHT	CAN communication signal (low) *1	Refer to CAN communication signal.
G20-12	RED	CAN communication signal (high) *1	Refer to CAN communication signal.
G20-13	YEL	Air intake control actuator (RECIRCULATION AIR)	10 – 14 V	Ignition: “ON” Air intake switch: “FRE” to “REC” position
G20-13	YEL	Air intake control actuator (RECIRCULATION AIR)	0 – 1 V	Ignition: “ON” Air intake switch: “REC” to “FRE” position
G20-15	PNK	Air intake control actuator (FRESH AIR)	10 – 14 V	Ignition: “ON” Air intake switch: “REC” to “FRE” position
G20-15	PNK	Air intake control actuator (FRESH AIR)	0 – 1 V	Ignition: “ON” Air intake switch: “FRE” to “REC” position
G20-17	PPL	Air flow control actuator (FACE)	10 – 14 V	Ignition: “ON” Air flow control actuator: “DEF” to “FACE” position
G20-17	PPL	Air flow control actuator (FACE)	0 – 1 V	Ignition: “ON” Air flow control actuator: in condition other than above
G20-18	BEG	Air flow control actuator (DEF)	10 – 14 V	Ignition: “ON” Air flow control actuator: “FACE” to “DEF” position
G20-18	BEG	Air flow control actuator (DEF)	0 – 1 V	Ignition: “ON” Air flow control actuator: in condition other than above
G20-19	RED	Temperature control actuator (HOT)	10 – 14 V	Ignition: “ON” Temperature control actuator: COOL to HOT position
G20-19	RED	Temperature control actuator (HOT)	0 – 1 V	Ignition: “ON” Temperature control actuator: in condition other than above
G20-20	BLU	Temperature control actuator (COOL)	10 – 14 V	Ignition: “ON” Temperature control actuator: HOT to COOL position
G20-20	BLU	Temperature control actuator (COOL)	0 – 1 V	Ignition: “ON” Temperature control actuator: in condition other than above
G20-21	GRY	Air flow control actuator position sensor signal	Approx. 4 V	Ignition: “ON” “MODE” switch: “FACE” position
G20-21	GRY	Air flow control actuator position sensor signal	Approx. 1.6 V	Ignition: “ON” Defroster switch: ON
G20-22	YEL	Temperature control actuator position sensor signal	Approx. 4.5 V	Ignition: “ON” Temperature selector: “MAX COOL” position
G20-22	YEL	Temperature control actuator position sensor signal	Approx. 0.5 V	Ignition: “ON” Temperature selector: “MAX HOT” position
G20-24	BLU	Inside air temperature sensor signal	Approx. 2.4 V	Ignition: “ON” Inside temperature: 25 °C (77 °F)
G20-25	LT BLU	Sunload sensor signal	Approx. 3 V	Ignition: “ON” Amount of sun load: 500 W/m²
G20-25	LT BLU	Sunload sensor signal	Approx. 5 V	Ignition: “ON” Amount of sun load: 0 W/m²
G20-28	BLU	Air intake control actuator position sensor signal	Approx. 3.9 V	Ignition: “ON” Air intake switch: “REC” position
G20-28	BLU	Air intake control actuator position sensor signal	Approx. 1.1 V	Ignition: “ON” Air intake switch: “FRE” position
G20-29	LT GRN	LIN communication signal *1	Refer to LIN communication signal.
G20-30	PNK	Rear defogger switch signal	0 – 1 V	Ignition: “ON” Rear defogger switch: OFF
G20-30	PNK	Rear defogger switch signal	10 – 14 V	Ignition: “ON” Rear defogger switch: ON
G20-33	GRY	Ground for HVAC control module	0 – 1 V	Ignition: “ON”
G20-35	LT GRN	Power supply for backup	Approx. 12 V	Any condition
G20-36	GRN	Blower motor controller *2	10 – 14 V	Ignition: “ON” Blower speed selector: OFF position
			Approx. 8.1 V	Ignition: “ON” Blower speed selector: 1st position
			Approx. 6.6 V	Ignition: “ON” Blower speed selector: 2nd position
			Approx. 5.2 V	Ignition: “ON” Blower speed selector: 3rd position
			Approx. 3.4 V	Ignition: “ON” Blower speed selector: 4th position
			Approx. 2.1 V	Ignition: “ON” Blower speed selector: 5th position
			Approx. 1.4 V	Ignition: “ON” Blower speed selector: 6th position
			Approx. 0.3 V	Ignition: “ON” Blower speed selector: 7th and 8th positions
G20-37	GRY	Blower motor control signal *2	0 – 1 V	Ignition: “ON” Blower speed selector: OFF position
			Approx. 4.5 V	Ignition: “ON” Blower speed selector: at each of 1st to 6th positions
			Approx. 9 V	Ignition: “ON” Blower speed selector: 7th and 8th positions
G20-38	YEL	Power supply	10 – 14 V	Ignition: “ON”

Reference Waveform

Oscilloscope display

Shown below is typical waveform display provided by oscilloscope.

NOTE:

•Display includes the following types of data:

[a]:	Waveform of channel 1	[c]:	VOLT/DIV of each channel
[b]:	Ground level of each channel	[d]:	TIME/DIV

•Waveform varies depending on measurement condition and vehicle spec.

LIN communication signal

Channel	Probe	Terminal No.
1	+	G20-29
1	–	G20-33

Measurement condition

•Ignition: “ON”

1.	LIN communication signal

CAN communication signal

CAN communication signal (High) (1)

Channel	Probe	Terminal No.
1	+	G20-12
1	–	G20-33

CAN communication signal (Low) (2)

Channel	Probe	Terminal No.
2	+	G20-11
2	–	G20-33

Measurement condition

•Ignition “ON”.