A/c-Heater System - Automatic: Diagnosis Lexus LS II

SELF-DIAGNOSTICS

An Electronic Control Unit (ECU) within A/C-heater control assembly monitors system circuits and stores trouble codes in memory if problems are detected. All codes, except Codes 22 and 23, are stored in memory. Malfunction is current if Code 22 or 23 is displayed. To retrieve stored codes, see RETRIEVING CODES. Codes are displayed at temperature display. see scheme 2

TESTING

ACC POWER SOURCE CIRCUIT TEST

1. Remove A/C-heater control assembly, leaving harness connectors attached. See «A/C-HEATER CONTROL ASSEMBLY»(ref-125187-S19345710212001100400000) under REMOVAL & INSTALLATION. Turn ignition on. Backprobe terminal A21-12 (Red wire) of A/C-heater control assembly connector and ground. see scheme 6
2. If battery voltage exists, no problem is indicated at this time. If battery voltage does not exist, inspect FR CIG fuse, located in instrument panel fuse block, behind parking brake release lever. If fuse is okay, inspect wiring between A/C-heater control assembly and battery. Repair as necessary. Replace fuse if blown, and inspect for short circuit. Repair as necessary.
3. Turn ignition off. Check continuity between terminal A21-11 (White/Black wire) and ground. Repair open White/Black wire if continuity does not exist.

AMBIENT TEMPERATURE SENSOR TEST

Remove radiator grille. Unplug ambient temperature sensor connector. see scheme 1 Measure resistance between sensor terminals while heating sensor. See AMBIENT TEMPERATURE SENSOR SPECIFICATIONS table. Replace sensor if resistance is not as specified.

AMBIENT TEMPERATURE SENSOR SPECIFICATIONS

AIR INLET DOOR POSITION SENSOR TEST

1. Remove heater unit. See «A/C-HEATER UNIT»(ref-125187-S32673217442001100400000) under REMOVAL & INSTALLATION. Unplug air inlet servomotor connector. Measure resistance between servomotor connector terminals No. 4 (Blue wire) and No. 5 (Yellow/Green wire).
2. If resistance is not 4700-7200 ohms, replace air inlet servomotor. If resistance is as specified, apply battery voltage to air inlet servomotor connector terminal No. 5 (Yellow/Green wire). Connect terminal No. 4 (Blue wire) to ground. (Scheme 6)
3. As servomotor operates, measure resistance. Transpose power leads. Again measure resistance. Resistance should be as specified for each door position. See «AIR INLET DOOR POSITION SENSOR»(ref-125187-S05781790632001100400000) SPECIFICATIONS table. If resistance is not as specified, replace air inlet door servomotor.

AIR INLET DOOR POSITION SENSOR SPECIFICATIONS

AIR INLET DOOR SERVOMOTOR TEST

1. Remove A/C unit and blower unit. See «A/C-HEATER UNIT»(ref-125187-S32673217442001100400000) and BLOWER UNIT under REMOVAL & INSTALLATION. Unplug air inlet servomotor connector. Connect battery voltage to terminal No. 5 (Yellow/Green wire). Connect terminal No. 4 (Blue wire) to ground. (Scheme 6)
2. Servomotor lever should move smoothly to recirculated air position. Transpose power leads. Servomotor lever should move smoothly to fresh air position. If lever does not operate as specified, replace servomotor.

Scheme 6

AIR MIX DOOR SERVOMOTOR TEST

Remove heater unit. See A/C-HEATER UNIT under REMOVAL & INSTALLATION. Unplug air mix servomotor connector. Connect ohmmeter positive lead to terminals No. 3 and 4. Connect ohmmeter negative lead, in turn, to each remaining terminal. (Scheme 7) If resistance is not 16-18 ohms at each step, replace air mix door servomotor.

Scheme 7

AIR MIX SERVOMOTOR CIRCUIT TEST

1. Warm engine to normal operating temperature. Perform «RETRIEVING CODES»(ref-125187-S05538850442001100400000) under TROUBLE SHOOTING. After system enters self-diagnostic mode, perform «ACTUATOR CHECK»(ref-125187-S02407909052001100400000) under TROUBLE SHOOTING. Press TEMP (up arrow) button to enter the step mode and display codes. See «AIR MIX DOOR AIRFLOW»(ref-125187-S33987075202001100400000) table. Air mix door operation should be as specified.
2. If air mix door functions as specified, no problem is indicated at this time. If air mix door does not function as specified, test air mix door servomotor. See «AIR MIX DOOR SERVOMOTOR»(ref-125187-S06037270102001100400000) . Replace air mix door servomotor as necessary. If servomotor is okay, go to next step.
3. Inspect wiring harness and connectors between servomotor and A/C-heater control assembly. Repair as necessary. If wiring harness and connectors are okay, substitute known-good A/C-heater control assembly. Retest system.

AIR MIX DOOR AIRFLOW

AIR VENT MODE DOOR SERVOMOTOR CIRCUIT TEST

1. Warm engine to normal operating temperature. Perform «RETRIEVING CODES»(ref-125187-S05538850442001100400000) under TROUBLE SHOOTING. After system enters self-diagnostic mode, perform «ACTUATOR CHECK»(ref-125187-S02407909052001100400000) under TROUBLE SHOOTING. Press TEMP (up arrow) button to enter the step mode and display codes. See «AIR VENT MODE DOOR SERVOMOTOR AIRFLOW OPERATION»(ref-125187-S38554565892001100400000) table. Servomotor door operation should be as specified.
2. If servomotor functions as specified, no problem is indicated at this time. If servomotor does not function as specified, go to next step. AIR VENT MODE DOOR SERVOMOTOR AIRFLOW OPERATION Code (1) Airflow Mode 0-3 Face 4-5 Bi-Level 6-7 Foot 8 Foot-Defrost 9 Defrost (1) Airflow mode should change as display codes change.
3. Remove heater unit. See «A/C-HEATER UNIT»(ref-125187-S32673217442001100400000) under REMOVAL & INSTALLATION. Unplug air vent servomotor connector. Connect ohmmeter positive lead to terminals No. 3 and 4. Connect ohmmeter negative lead, in turn, to each remaining terminals. (Scheme 7) Resistance should be 16-18 ohms. If resistance is not as specified, replace air vent door servomotor.
4. If resistance is as specified, inspect wiring between A/C-heater control assembly and servomotor, and between battery, servomotor and ground. Repair or replace wiring as necessary. If wiring is okay, temporarily substitute known-good A/C-heater control assembly. Retest system.

BACK-UP POWER SOURCE CIRCUIT TEST

1. Remove A/C-heater control assembly, leaving harness connectors attached. See «A/C-HEATER CONTROL ASSEMBLY»(ref-125187-S19345710212001100400000) under REMOVAL & INSTALLATION. Turn ignition on. Backprobe terminal A21-1 (White/Red wire) of A/C-heater control assembly connector to ground. see scheme 6
2. If battery voltage exists, no problem is indicated at this time. If battery voltage does not exist, inspect FUEL OPEN fuse. see scheme 4 If fuse is okay, inspect wiring harness between A/C-heater control assembly and battery. Repair wiring as necessary.

BLOWER MOTOR CIRCUIT TEST

1. Remove blower motor. See «BLOWER MOTOR»(ref-125187-S21923080072001100400000) under REMOVAL & INSTALLATION. Connect battery voltage to blower motor connector terminal No. 2 (Red wire). Connect terminal No. 1 (Black wire) to ground. If blower motor operates smoothly, go to next step. Replace blower motor if it does not operate smoothly.
2. Remove A/C-heater control assembly, leaving connectors attached. Check pulse signal between terminal A18-17 (Light Green/Red wire) and A21-11 (White/Black wire). If pulse signal is not present, replace A/C-heater control assembly.
3. If pulse signal is present, inspect wiring between battery and blower motor, and between blower motor and ground. Repair as necessary. If wiring is okay, replace blower controller.

COMPRESSOR CIRCUIT TEST

1. Remove A/C-heater control assembly, leaving harness connectors attached. Turn ignition on. Press any fan speed switch. Backprobe between terminal A20-9 (Black/White wire) of A/C-heater control assembly connector and ground. see scheme 6
2. Turn A/C system on. Voltmeter should indicate battery voltage. Turn A/C system off. Voltmeter should indicate zero volts. If compressor circuit voltage is as specified, go to next step. If compressor circuit voltage is not as specified, go to step 5).
3. Unplug compressor clutch connector. Apply battery voltage to compressor clutch connector terminal. If compressor clutch does not engage, repair or replace compressor clutch.
4. If compressor clutch engages, inspect wiring harness and connectors between compressor clutch relay and compressor clutch. Repair as necessary. If wiring harness and connectors are okay, test ignitor circuit. See «IGNITOR CIRCUIT»(ref-125187-S23327484502001100400000).
5. Turn ignition on. Press any fan speed switch. Backprobe between terminal A18-14 (Black/Red wire) of A/C-heater control assembly connector and ground. With A/C system on, voltage should be zero volts. With A/C off voltage should be 10-14 volts. If voltage is as specified, go to step 8). If voltage is not as specified, go to next step.
6. Unplug A/C-heater control assembly connector. Turn ignition on. Measure voltage between terminal A18-14 (Black/Red wire) of A/C-heater control assembly connector and ground. If voltage is 10-14 volts, temporarily substitute known-good A/C-heater control assembly. Retest system. If voltage is not 10-14 volts, go to next step.
7. Inspect wiring harness and connectors between A/C-heater control assembly and Electronic Control Module (ECM). Repair as necessary. If wiring harness and connectors are okay, temporarily substitute known-good ECM. Retest system.
8. Remove compressor clutch relay. Check continuity between relay terminals. Continuity should exist between terminals No. 1 and 3. (Scheme 8) Continuity should not exist between terminals No. 2 and 4.
9. Apply battery voltage to relay terminal No. 1. Connect terminal No. 3 to ground. Continuity should exist between terminals No. 2 and 4. If continuity is not as specified, replace compressor clutch relay. If continuity is as specified, go to next step.
10. Remove ECM, leaving harness connectors attached. ECM is located behind glove box. Turn ignition on. Press any fan speed switch. Backprobe between terminal A/C MG (White wire) of ECM connector and ground. (Scheme 10)
11. With A/C system on, voltmeter should indicate about 1.3 volts. With A/C system off, voltage should be between 1.3 volts and battery voltage. If voltage is not as specified, inspect wiring harness and connectors between ECM and battery. Repair as necessary. If wiring harness and connectors are okay, temporarily substitute known-good ECM. Retest system.
12. If voltage is as specified, inspect wiring harness and connectors between A/C-heater control assembly and compressor relay, and between compressor relay and battery. Repair or replace wiring as necessary. If wiring is okay, temporarily substitute known-good A/C-heater control assembly. Retest system.

Scheme 8

Scheme 9

Scheme 10

COMPRESSOR LOCK SENSOR TEST

Raise and support vehicle. Unplug compressor lock sensor connector. Measure resistance between sensor terminals. If resistance is not as specified, replace sensor. See COMPRESSOR LOCK SENSOR SPECIFICATIONS table.

COMPRESSOR LOCK SENSOR SPECIFICATIONS

On-Vehicle Inspection

1. With ignition on, A/C off, and coolant temperature at less than 181°F (83°C), cooling fan should be off. With ignition on, A/C off, and coolant temperature at 194°F (90°C) or higher, cooling fan should run at high speed.
2. With A/C on, coolant temperature less than 181°F (83°C) and refrigerant pressure at 220 psi (15.5 kg/cm 2 ) or higher, cooling fan should run at low speed. With A/C on, coolant temperature at 194°F (90°C) and refrigerant pressure at 220 psi (15.5 kg/cm 2 ) or higher, cooling fan should run at high speed. If cooling fan operation is not as specified, inspect coolant temperature switch, cooling fan relays, cooling fan motor, and associated wiring.

DUCT SENSORS TEST

Remove instrument panel. See INSTRUMENT PANEL under REMOVAL & INSTALLATION. Remove appropriate sensor for testing. Measure resistance between sensor terminals at specified temperatures. See DUCT SENSOR RESISTANCE SPECIFICATIONS table. If resistance is not as specified, replace sensor.

DUCT SENSOR RESISTANCE SPECIFICATIONS

EVAPORATOR TEMPERATURE SENSOR TEST

Remove evaporator temperature sensor. See EVAPORATOR TEMPERATURE SENSOR under REMOVAL & INSTALLATION. Measure resistance between sensor terminals. See EVAPORATOR TEMPERATURE SENSOR SPECIFICATIONS table. If resistance is not as specified, replace sensor.

EVAPORATOR TEMPERATURE SENSOR SPECIFICATIONS

HEATER RELAY CIRCUIT TEST

1. Remove A/C-heater control assembly, leaving harness connectors attached. See «A/C-HEATER CONTROL ASSEMBLY»(ref-125187-S19345710212001100400000) under REMOVAL & INSTALLATION. Turn ignition on.
2. Backprobe between terminal A18-18 (Blue/Yellow wire) of A/C-heater control assembly connector and ground. see scheme 6 If voltage is as specified, no problem is indicated at this time. See «HEATER RELAY CIRCUIT SPECIFICATIONS»(ref-125187-S04637727102001100400000) table.
3. If voltage is not as specified, remove heater relay. Check continuity between relay terminals. Continuity should exist between terminals No. 3 and 5, and between terminals No. 2 and 4. (Scheme 8) Continuity should not exist between terminals No. 1 and 4.
4. Apply battery voltage to terminal No. 3. Connect terminal No. 5 to ground. Continuity should exist between terminals No. 1 and 2. Continuity should not exist between terminals No. 2 and 4.
5. If continuity is not as specified, replace heater relay. If continuity is as specified, inspect heater fuse. If fuse is okay, inspect wiring between A/C-heater control assembly and battery. Repair wiring as necessary. If fuse is blown, replace fuse and check for short circuit.

HEATER RELAY CIRCUIT SPECIFICATIONS

IG POWER SOURCE CIRCUIT TEST

1. Remove A/C-heater control assembly, leaving harness connectors attached. See «A/C-HEATER CONTROL ASSEMBLY»(ref-125187-S19345710212001100400000) under REMOVAL & INSTALLATION. Turn ignition on. Backprobe between terminals A21-2 (Red/Blue wire) and A21-11 (White/Black wire) of A/C-heater control assembly connector. see scheme 6
2. If battery voltage exists, no problem is indicated at this time. If battery voltage does not exist, turn ignition off. Check continuity between A/C-heater control assembly connector terminal A21-11 (White/Black wire) and ground. If continuity exists, go to next step. If continuity does not exist, repair wiring between terminal A21-11 (White/Black wire) and body ground.
3. Inspect heater fuse. If fuse is okay, inspect wiring harness and connectors between A/C-heater control assembly and battery. Repair as necessary. If fuse is blown, replace fuse and inspect for short circuit.

IGNITOR CIRCUIT TEST

Check tachometer operation. If tachometer does not function properly, repair or replace tachometer. If tachometer functions properly, inspect Black/Yellow wire and associated connectors between A/C-heater control assembly and ignitor. Ignitor is located on right side of engine compartment. Repair wiring as necessary.

IN-VEHICLE TEMPERATURE SENSOR TEST

Remove left instrument panel undercover. Unplug in-vehicle temperature sensor. see scheme 1 Measure resistance between in-vehicle temperature sensor terminals while heating the sensor. See IN-VEHICLE TEMPERATURE SENSOR SPECIFICATIONS table. If resistance is not as specified, replace sensor.

IN-VEHICLE TEMPERATURE SENSOR SPECIFICATIONS

MAXIMUM COOL DOOR POSITION SENSOR TEST

1. Remove heater unit. See «A/C-HEATER UNIT»(ref-125187-S32673217442001100400000) under REMOVAL & INSTALLATION. Unplug maximum cool door servomotor connector. Measure resistance between servomotor connector terminals No. 1 (Yellow/Green wire) and No. 3 (Blue/White wire for driver's side servomotor; Blue wire for passenger's side servomotor).
2. If resistance is not 4700-7200 ohms, replace maximum cool door servomotor. If resistance is 4700-7200 ohms, apply battery voltage to servomotor connector terminal No. 5 (Light Green wire). (Scheme 11) Connect terminal No. 4 (Violet/Yellow wire) to ground.
3. As servomotor operates, observe ohmmeter. Transpose power leads, and observe ohmmeter. Resistance should be as specified for each door position. See «MAXIMUM COOL DOOR POSITION SENSOR»(ref-125187-S25446099222001100400000) SPECIFICATIONS table. If resistance is not as specified, replace maximum cool door servomotor.

MAXIMUM COOL DOOR POSITION SENSOR SPECIFICATIONS

Scheme 11

MAXIMUM COOL DOOR SERVOMOTOR TEST

1. Remove heater unit. See «A/C-HEATER UNIT»(ref-125187-S32673217442001100400000) under REMOVAL & INSTALLATION. Unplug appropriate maximum cool door servomotor connector. Connect battery voltage to servomotor terminal No. 5 (Light Green wire). (Scheme 11) Connect terminal No. 4 (Violet/Yellow wire) to ground.
2. Servomotor lever should move smoothly to closed position. Transpose power leads. Servomotor lever should move smoothly to open position. If lever does not function as specified, replace servomotor.

PRESSURE SWITCH TEST

1. Pressure switch is located near receiver-drier. (Scheme 12) Install manifold gauge set. Turn ignition on. Start engine. Turn blower and A/C on. Observe system pressure. Unplug pressure switch connector. Check continuity between pressure switch terminals No. 1 and 4.
2. Continuity should not exist if high side pressure is less than 28 psi (2.0 kg/cm 2 ) or greater than 455 psi (32 kg/cm 2 ). Continuity should exist if high side pressure is 28-455 psi (2.0-32 kg/cm 2 ). If continuity is not as specified, replace pressure switch.

Scheme 12

SELF-DIAGNOSTIC CIRCUIT TEST

1. Turn ignition on. Using a DVOM, measure voltage between terminals TC and EI of Data Link Connector No. 2 (DLC2). (Scheme 13) DLC2 is located behind left side of instrument panel. If battery voltage exists, no problem is indicated at this time.
2. If battery voltage does not exist, inspect wiring harness and connectors between A/C control panel, DLC2 and ground. Repair as necessary. If wiring and connectors are okay, temporarily substitute known-good A/C-heater control assembly. Retest system.

Scheme 13