A/c-Heater System - Automatic Lexus LS I

A/C SYSTEM SPECIFICATIONS

A/C SYSTEM SPECIFICATIONS

DESCRIPTION

Automatic A/C-heater system uses a microprocessor located in A/C control assembly to control air conditioning. The microprocessor uses inputs from various sensors, switches and motors to adjust selected air temperature. A/C system components include compressor, evaporator, receiver-drier, coolant temperature sensor and switch, ambient temperature sensor, pressure switch, solar sensor, blower and related vents and wiring. (Scheme 1)

Scheme 1

CONTROL PANEL

The A/C control (panel) assembly consists of a liquid crystal display and various push buttons to activate A/C system, set desired temperature, direct discharged air to proper vents, activate rear defogger and control blower fan speed. Display also has a clock. (Scheme 2)

Scheme 2

SENSORS

Resistance of all temperature sensors decreases as detected temperature increases. Solar sensor resistance is infinite (no continuity) when no light is directed at sensor. When sensor is subjected to bright light, resistance is approximately 4000 ohms. As light intensity decreases, solar sensor resistance increases.

PRESSURE SWITCH

Pressure switch is mounted on the receiver-drier to protect A/C system from high pressure build-up (due to restriction, overcharge or compressor malfunction). If excessively low or high pressure is sensed within the system, pressure switch electrically stops compressor clutch operation.

AIR INLET SERVOMOTOR

Air inlet servomotor is attached to cooling and blower unit. Servomotor rotates air inlet door so air is drawn from either inside (cabin air) or outside (fresh air). Motor rotation is transferred to a lever which moves air inlet doors.

AIR MIX SERVOMOTOR

Air mix servomotor is attached to heater unit. Servomotor rotates so air is drawn through heater core or evaporator. Servomotor rotation is transferred to a link which moves air mix door.

MAXIMUM COOL SERVOMOTOR

Maximum cool servomotor is attached to heater unit. Servomotor rotates so extra air is discharged to cool air in cabin. Servomotor rotation is transferred to control plates which move the maximum cool doors.

MODE SERVOMOTOR

Mode servomotor is attached to heater unit. Servomotor rotates so air is discharged from appropriate outlets set by control panel. Servomotor rotation is transferred to a link which moves mode door.

SELF-DIAGNOSTICS

A/C control assembly monitors system circuits and stores a code in memory if a problem is detected. To retrieve stored codes, see RETRIEVING CODES under TROUBLE SHOOTING. Codes are displayed at temperature display. (Scheme 2)

Indicator Check

1. Press and hold AUTO and REC switches. (Scheme 2) Turn ignition on. Ensure all indicators flash on and off 4 times, at one-second intervals. Ensure buzzer sounds when indicators light up.
2. To end indicator check, press and release OFF switch. A/C system will automatically go into diagnostic code check. See DIAGNOSTIC CODE CHECK.

Diagnostic Code Check

1. Read codes at temperature display. (Scheme 2) If a normal code (Code 00) is displayed but problem persists, go to matrix chart of problem symptoms. (Scheme 3) Trouble shoot symptom in numeric order from smallest to largest.
2. If trouble code is displayed, proceed to appropriate trouble shooting procedure. See «DIAGNOSTIC CODE IDENTIFICATION»(/lexus/ls/i-1989-1994/remont/automatic-hvac-system/#ac-heater-system-automatic) table. Codes are displayed in ascending order. To slow rate at which codes are displayed, press UP switch to change display to step operation. Each time UP switch is pressed, display changes by one step.
3. If buzzer sounds as a code is read, problem currently exists. If buzzer does not sound while code is read, problem has occurred and is not presently detected (intermittent). If ambient temperature is -22°F (-30°C) or less, a code may be displayed even though system is functioning normally.

Note. If testing is done in a dark area, Code 21 may be displayed. In this case, shine a light at solar sensor and perform diagnostic code check again. See DIAGNOSTIC CODE CHECK. If Code 21 is displayed again, check solar sensor circuit.

DIAGNOSTIC CODE IDENTIFICATION

Scheme 3

CLEARING CODES

Remove the DOME fuse from junction block No. 2 for at least 10 seconds. (Scheme 4) Install the DOME fuse. Retrieve codes. Refer to RETRIEVING CODES. Ensure Code 00 is displayed.

Scheme 4

Voltage Check

1. Remove A/C control assembly with harness connectors attached. (Scheme 1) Turn ignition on. Using a voltmeter, backprobe terminals TR (positive) and SG (negative) of A/C control assembly 16-pin harness connector. (Scheme 5)
2. Heat room temperature sensor and measure circuit voltage. See «ROOM TEMP SENSOR CIRCUIT VOLTAGE SPECIFICATIONS»(/lexus/ls/i-1989-1994/remont/automatic-hvac-system/#ac-heater-system-automatic) table. ROOM TEMP SENSOR CIRCUIT VOLTAGE SPECIFICATIONS Sensor Temperature (1) Volts 77°F (25°C) 1.8-2.2 104°F (40°C) 1.2-1.6 (1) As temperature increases, voltage should decrease gradually.
3. If circuit voltage is not as specified, test sensor resistance. See SENSOR RESISTANCE TEST. If circuit voltage is within specification, go to next step.
4. If Code 11 is displayed, check and replace A/C control assembly as necessary. If Code 11 is not displayed, go to circuit with next highest number in matrix chart (for appropriate symptom). (Scheme 3)

Sensor Resistance Test

1. Remove left instrument panel undercover, and disconnect room temperature sensor. (Scheme 1) Using an ohmmeter, check resistance between room temperature sensor terminals while heating sensor. See «ROOM TEMP SENSOR RESISTANCE SPECIFICATIONS»(/lexus/ls/i-1989-1994/remont/automatic-hvac-system/#ac-heater-system-automatic) table.
2. If resistance is not as specified, replace sensor. If resistance is within specification, check wiring harness and connectors between sensor and A/C control assembly. Repair as necessary. If wiring harness and connectors are okay, replace A/C control assembly.

ROOM TEMP SENSOR RESISTANCE SPECIFICATIONS

Scheme 5

1. Remove A/C control assembly with harness connectors attached. (Scheme 1) Turn ignition on. Using a voltmeter, backprobe terminals TAM (positive) and SG (negative) of A/C control assembly 16-pin harness connector. (Scheme 5)
2. Heat ambient temperature sensor and measure circuit voltage. See «AMBIENT TEMP SENSOR CIRCUIT VOLTAGE SPECIFICATIONS»(/lexus/ls/i-1989-1994/remont/automatic-hvac-system/#ac-heater-system-automatic) table. AMBIENT TEMP SENSOR CIRCUIT VOLTAGE SPECIFICATIONS Sensor Temperature (1) Volts 77°F (25°C) 1.35-1.75 104°F (40°C).85-1.25 (1) As temperature increases, voltage should decrease gradually.
3. If circuit voltage is not as specified, test sensor resistance. See SENSOR RESISTANCE TEST. If circuit voltage is within specification, go to next step.
4. If Code 12 is displayed, check and replace A/C control assembly as necessary. If Code 12 is not displayed, go to circuit with next highest number in matrix chart (for appropriate symptom). (Scheme 3)

1. Remove front radiator grille, and disconnect ambient temperature sensor. (Scheme 1) Using an ohmmeter, check the resistance between the terminals of sensor while heating sensor. See «AMBIENT TEMP SENSOR RESISTANCE SPECIFICATIONS»(/lexus/ls/i-1989-1994/remont/automatic-hvac-system/#ac-heater-system-automatic) table.
2. If resistance is not as specified, replace sensor. If resistance is within specification, check wiring harness and connectors between sensor and A/C control assembly. Repair as necessary. If wiring harness and connectors are okay, replace A/C control assembly.

AMBIENT TEMP SENSOR RESISTANCE SPECIFICATIONS

1. Remove A/C control assembly with harness connectors attached. (Scheme 1) Turn ignition on. Using a voltmeter, backprobe terminals TE (positive) and SG (negative) of A/C control assembly 16-pin harness connector. (Scheme 5)
2. Measure evaporator temperature sensor circuit voltage. See «EVAPORATOR TEMP SENSOR CIRCUIT VOLTAGE SPECIFICATIONS»(/lexus/ls/i-1989-1994/remont/automatic-hvac-system/#ac-heater-system-automatic) table. EVAPORATOR TEMP SENSOR CIRCUIT VOLTAGE SPECIFICATIONS Sensor Temperature (1) Volts 32°F (0°C) 2.0-2.4 59°F (15°C) 1.4-1.8 (1) As temperature increases, voltage should decrease gradually.
3. If circuit voltage is not as specified, test sensor resistance. See SENSOR RESISTANCE TEST. If circuit voltage is within specification, go to next step.
4. If Code 13 is displayed, check and replace A/C control assembly as necessary. If Code 13 is not displayed, go to circuit with next highest number in matrix chart (for appropriate symptom). (Scheme 3)

1. Remove evaporator temperature sensor. See «EVAPORATOR»(/lexus/ls/i-1989-1994/remont/automatic-hvac-system/#ac-heater-system-automatic) SENSOR under REMOVAL & INSTALLATION. Using an ohmmeter, check resistance between terminals of sensor. See «EVAPORATOR TEMP SENSOR»(/lexus/ls/i-1989-1994/remont/automatic-hvac-system/#ac-heater-system-automatic) RESISTANCE SPECIFICATIONS table.
2. If resistance is not as specified, replace sensor. If resistance is within specification, check wiring harness and connectors between sensor and A/C control assembly. Repair as necessary. If wiring harness and connectors are okay, replace A/C control assembly.

EVAPORATOR TEMP SENSOR RESISTANCE SPECIFICATIONS

1. Remove A/C control assembly with harness connectors attached. (Scheme 1) Turn ignition on. Using a voltmeter, backprobe terminals TW (positive) and SG (negative) of A/C control assembly 16-pin harness connector. (Scheme 5) Measure sensor circuit voltage. See «COOLANT TEMP SENSOR CIRCUIT VOLTAGE SPECIFICATIONS»(/lexus/ls/i-1989-1994/remont/automatic-hvac-system/#ac-heater-system-automatic) table. COOLANT TEMP SENSOR CIRCUIT VOLTAGE SPECIFICATIONS Sensor Temperature (1) Volts 32°F (0°C) 2.8-3.2 104°F (40°C) 1.8-2.2 158°F (70°C).9-1.3 (1) As temperature increases, voltage should decrease gradually.
2. If circuit voltage is not as specified, test sensor resistance. See SENSOR RESISTANCE TEST. If circuit voltage is within specification, go to next step.
3. If Code 14 is displayed, check and replace A/C control assembly as necessary. If Code 14 is not displayed, go to circuit with next highest number in matrix chart (for appropriate symptom). (Scheme 3)

1. Remove coolant temperature sensor. See «HEATER UNIT»(/lexus/ls/i-1989-1994/remont/automatic-hvac-system/#ac-heater-system-automatic) under REMOVAL & INSTALLATION. Place sensor in water. Using an ohmmeter, check resistance between sensor terminals No. 1 and 3. (Scheme 6) See «COOLANT TEMP SENSOR RESISTANCE SPECIFICATIONS»(/lexus/ls/i-1989-1994/remont/automatic-hvac-system/#ac-heater-system-automatic) table.
2. If resistance is not as specified, replace sensor. If resistance is within specification, check wiring harness and connectors between sensor and A/C control assembly. Repair or replace as necessary. If wiring harness and connectors are okay, replace A/C control assembly.

COOLANT TEMP SENSOR RESISTANCE SPECIFICATIONS

Scheme 6

1. Remove A/C control assembly with harness connectors attached. See ff (Scheme 1). Turn ignition on. Using a voltmeter, backprobe terminals S5 (positive) and TS (negative) of A/C control assembly 16-pin harness connector. (Scheme 5) Measure sensor circuit voltage. See «SOLAR SENSOR CIRCUIT VOLTAGE SPECIFICATIONS»(/lexus/ls/i-1989-1994/remont/automatic-hvac-system/#ac-heater-system-automatic) table. SOLAR SENSOR CIRCUIT VOLTAGE SPECIFICATIONS Condition (1) Volts Sensor Subjected To Bright Light Less Than 4.0 Sensor Covered By Cloth 4.0-4.5 (1) As light intensity decreases, voltage should increase.
2. If circuit voltage is not as specified, test sensor resistance. See SENSOR RESISTANCE TEST. If circuit voltage is within specification, go to next step.
3. If Code 21 is displayed, check and replace A/C control assembly as necessary. If Code 21 is not displayed, go to circuit with next highest number in matrix chart (for appropriate symptom). (Scheme 3)

1. Remove glove box. Disconnect solar sensor harness connector. Cover sensor using cloth. Using an ohmmeter, check resistance between sensor terminals. Remove cloth. Subject sensor to bright light and check resistance between terminals of sensor. See «SOLAR SENSOR RESISTANCE SPECIFICATIONS»(/lexus/ls/i-1989-1994/remont/automatic-hvac-system/#ac-heater-system-automatic) table.
2. If resistance is not as specified, replace sensor. If resistance is within specification, check wiring harness and connectors between sensor and A/C control assembly. Repair or replace as necessary. If wiring harness and connectors are okay, replace A/C control assembly.

SOLAR SENSOR RESISTANCE SPECIFICATIONS

Compressor Drive Belt Check

1. Ensure drive belt fits properly in ribbed grooves of compressor pulley. Ensure tension is in range "A" on auto tensioner scale. (Scheme 7) If tension is not in range "A" on scale, replace belt. If tension is okay, go to next step. NOTE: When replacing drive belt, new belt tension should be in range "B" on tensioner scale. (Scheme 7)
2. Start engine. Turn blower and A/C on. Ensure compressor does not lock during operation. If compressor locks during operation, repair compressor. If compressor does not lock during operation, test sensor resistance. See SENSOR RESISTANCE TEST.

Scheme 7

1. Raise and support vehicle. Disconnect compressor lock sensor connector. Using an ohmmeter, check resistance between sensor terminals.
2. If resistance is not 400-600 ohms, replace sensor. If resistance is 400-600 ohms, check wiring harness and connectors between sensor and A/C control assembly. Repair or replace as necessary. If wiring harness and connectors are okay, go to next step.
3. If Code 22 is displayed, check and replace A/C control assembly as necessary. If Code 22 is not displayed, go to circuit with next highest number in matrix chart (for appropriate symptom). (Scheme 3)

CODE 31 OR 33 - AIR MIX DAMPER POSITION SENSOR CIRCUIT

Note. For Code 33, also see CODE 33 - AIR MIX SERVOMOTOR CIRCUIT for additional trouble shooting procedures.

1. Remove A/C control assembly with harness connectors attached. Turn ignition on. Using a voltmeter, check voltage by backprobing terminals TP (positive) and SG (negative) of A/C control assembly 16-pin harness connector. (Scheme 5)
2. Measure sensor circuit voltage while changing set temperature to activate air mix damper. See «AIR MIX DAMPER POSITION»(/lexus/ls/i-1989-1994/remont/automatic-hvac-system/#ac-heater-system-automatic) SENSOR CIRCUIT VOLTAGE SPECIFICATIONS table. AIR MIX DAMPER POSITION SENSOR CIRCUIT VOLTAGE SPECIFICATIONS Set Temperature (1) Volts Maximum Cool Approx. 4 Maximum Hot Approx. 1 (1) As set temperature increases, voltage should decrease gradually.
3. If circuit voltage is not as specified, test sensor resistance. See SENSOR RESISTANCE TEST. If circuit voltage is within specification, go to next step.
4. If Code 31 or 33 is displayed, check and replace A/C control assembly as necessary. If neither Code 31 nor 33 is displayed, go to circuit with next highest number in matrix chart (for appropriate symptom). (Scheme 3)

1. Remove heater unit. See «HEATER UNIT»(/lexus/ls/i-1989-1994/remont/automatic-hvac-system/#ac-heater-system-automatic) under REMOVAL & INSTALLATION. Disconnect air mix servomotor connector. Using an ohmmeter, check resistance between servomotor connector terminals No. 1 and 3. (Scheme 8)
2. Resistance should be 4700-7200 ohms. If resistance is not as specified, replace air mix servomotor assembly. If resistance is as specified, go to next step.
3. Move servomotor to maximum cold position by applying battery voltage to air mix servomotor assembly connector terminal No. 2 and grounding terminal No. 6.
4. Measure resistance between terminals No. 3 and 4. See «AIR MIX DAMPER POSITION SENSOR RESISTANCE SPECIFICATIONS»(/lexus/ls/i-1989-1994/remont/automatic-hvac-system/#ac-heater-system-automatic) table. Move servomotor to maximum hot position by reversing leads to battery and ground.
5. If resistance is not as specified, replace air mix servomotor assembly. If resistance is within specification, check wiring harness and connectors between air mix servomotor and A/C control assembly. Repair or replace as necessary. If wiring harness and connectors are okay, replace A/C control assembly.

AIR MIX DAMPER POSITION SENSOR RESISTANCE SPECIFICATIONS

Scheme 8

CODE 32 OR 34 - AIR INLET DAMPER POSITION SENSOR CIRCUIT

Note. For Code 34, also see CODE 34 - AIR INLET SERVOMOTOR CIRCUIT for additional trouble shooting procedures.

1. Remove A/C control assembly with harness connectors attached. (Scheme 1) Turn ignition on. Using a voltmeter, check circuit voltage by backprobing A/C control assembly 16-pin harness connector terminals TPI (positive) and SG (negative). (Scheme 5)
2. Measure sensor circuit voltage while pressing REC/FRS switch to change air inlet between fresh air and recirculation air. (Scheme 2) See AIR INLET DAMPER POSITION SENSOR CIRCUIT VOLTAGE SPECIFICATIONS table. AIR INLET DAMPER POSITION SENSOR CIRCUIT VOLTAGE SPECIFICATIONS Switch/Inlet Position (1) Volts Recirculation (REC) Approx. 4 Fresh (FRS) Approx. 1 (1) Voltage should decrease gradually as air inlet damper changes from REC to FRS position.
3. If circuit voltage is not as specified, test sensor resistance. See SENSOR RESISTANCE TEST. If circuit voltage is within specification, go to next step.
4. If Code 32 or 34 is displayed, check and replace A/C control assembly as necessary. If neither Code 32 nor 34 is displayed, go to circuit with next highest number in matrix chart (for appropriate symptom). See f (Scheme 3).

1. Remove heater unit. See «HEATER UNIT»(/lexus/ls/i-1989-1994/remont/automatic-hvac-system/#ac-heater-system-automatic) under REMOVAL & INSTALLATION. Disconnect air inlet servomotor assembly connector. Using an ohmmeter, check resistance between sensor terminals No. 1 and 3. (Scheme 8)
2. Resistance should be 4700-7200 ohms. If resistance is not as specified, replace air inlet servomotor assembly. If resistance is 4700-7200 ohms, go to next step.
3. Move servomotor to recirculated air (REC) position by applying battery voltage to servomotor assembly connector terminal No. 5 and grounding terminal No. 4. (Scheme 8)
4. Measure and record resistance between terminals No. 2 and 3. Move servomotor to fresh air (FRS) position by reversing leads to battery and ground. Check resistance between terminals No. 2 and 3 again.
5. See «AIR INLET DAMPER POSITION SENSOR RESISTANCE»(/lexus/ls/i-1989-1994/remont/automatic-hvac-system/#ac-heater-system-automatic) SPECIFICATIONS table. If resistance is not as specified, replace air inlet servomotor assembly. If resistance is within specification, check wiring harness and connectors between air inlet servomotor assembly and A/C control assembly. Repair or replace as necessary. If wiring harness and connectors are okay, replace A/C control assembly.

AIR INLET DAMPER POSITION SENSOR RESISTANCE SPECIFICATIONS

Actuator Check

1. Warm engine to normal operating temperature. Perform INDICATOR CHECK. See «RETRIEVING CODES»(/lexus/ls/i-1989-1994/remont/automatic-hvac-system/#ac-heater-system-automatic) under TROUBLE SHOOTING. After system enters DIAGNOSTIC CODE CHECK, press REC switch. (Scheme 2)
2. Press UP switch to display appropriate display codes. See «AIR MIX DAMPER AIRFLOW»(/lexus/ls/i-1989-1994/remont/automatic-hvac-system/#ac-heater-system-automatic) table. Ensure air mix damper operation is as specified.
3. If air mix damper functions as specified, go to circuit with next highest number in matrix chart (for appropriate symptom). (Scheme 3) If air mix damper does not function as specified, check air mix servomotor. See AIR MIX SERVOMOTOR TEST.

AIR MIX DAMPER AIRFLOW

Air Mix Servomotor Test

1. Remove heater unit. See «HEATER UNIT»(/lexus/ls/i-1989-1994/remont/automatic-hvac-system/#ac-heater-system-automatic) under REMOVAL & INSTALLATION. Disconnect air mix servomotor assembly connector.
2. Apply battery voltage to air mix servomotor assembly connector terminal No. 2, and ground terminal No. 6. (Scheme 9) Ensure air mix servomotor lever moves to COOL position. Reverse battery and ground leads. Ensure servomotor lever moves to WARM position.
3. If air mix servomotor does not function as described, replace air mix servomotor assembly. If servomotor functions correctly, check wiring harness and connectors between servomotor and A/C control assembly. Repair or replace as necessary. If wiring harness and connectors are okay, replace A/C control assembly.

Scheme 9

1. Remove glove box, and check air inlet damper operation. Perform INDICATOR CHECK. See «RETRIEVING CODES»(/lexus/ls/i-1989-1994/remont/automatic-hvac-system/#ac-heater-system-automatic) under TROUBLE SHOOTING. After system enters DIAGNOSTIC CODE CHECK, press REC switch. (Scheme 2)
2. Press UP switch to display appropriate display codes. See «AIR INLET DAMPER AIRFLOW»(/lexus/ls/i-1989-1994/remont/automatic-hvac-system/#ac-heater-system-automatic) table. Ensure air inlet damper operation is as specified in table. (Scheme 10) AIR INLET DAMPER AIRFLOW Display Code Air Inlet Damper 20 & 21 FRS 22 F/R 23 REC 24-29 FRS
3. If air inlet damper functions as specified, go to circuit with next highest number in matrix chart (for appropriate symptom). (Scheme 3) If air inlet damper does not function as specified, check air inlet servomotor. See AIR INLET SERVOMOTOR TEST.

Scheme 10

Air Inlet Servomotor Test

1. Remove cooling unit. See «COOLING & BLOWER UNIT»(/lexus/ls/i-1989-1994/remont/automatic-hvac-system/#ac-heater-system-automatic) under REMOVAL & INSTALLATION. Disconnect air inlet servomotor assembly connector.
2. Apply battery voltage to air inlet servomotor assembly connector terminal No. 5, and ground terminal No. 4. (Scheme 11) Ensure air inlet servomotor lever moves to REC position. Reverse battery and ground connections. Ensure air inlet servomotor lever moves to FRS position.
3. If air inlet servomotor does not operate as described, replace air inlet servomotor assembly. If servomotor operates correctly, check wiring harness and connectors between servomotor and A/C control assembly. Repair or replace as necessary. If wiring harness and connectors are okay, replace A/C control assembly.

Scheme 11

TESTING

1. Remove A/C control assembly with harness connectors attached. Measure voltage between ground and terminal "B" of A/C control assembly 18-pin harness connector. (Scheme 5)
2. If battery voltage is present, go to circuit with next highest number on matrix chart (for appropriate symptom). (Scheme 3) If battery voltage is not present, check DOME fuse in junction block No. 2. (Scheme 4) If fuse is okay, check wiring harness between A/C control assembly and battery. Repair as necessary.

1. Remove A/C control assembly with harness connectors attached. (Scheme 1) Turn ignition on. Measure voltage between terminals IG and GND of A/C control assembly 18-pin harness connector. (Scheme 5)
2. If battery voltage is present, go to circuit with next highest number on matrix chart (for appropriate symptom). (Scheme 3) If battery voltage is not present, check ground wire.

Ground Wire Check

Turn ignition off. Check continuity between ground and A/C control assembly 18-pin harness connector terminal GND. If continuity exists, check heater fuse. See HTR FUSE CHECK. If continuity does not exist, repair wiring harness or connector.

HTR Fuse Check

Remove fuse from junction block No. 1 located below dash, on driver side. (Scheme 12) Check continuity of fuse. If fuse is okay, check harness or connector between A/C control assembly and battery. Repair as necessary. If fuse is blown, replace fuse, and check for short circuit.

Scheme 12

1. Remove A/C control assembly with harness connectors attached. (Scheme 1) Turn ignition on. Measure voltage between terminal ACC of A/C control assembly 18-pin harness connector and ground. (Scheme 5)
2. If battery voltage is present, go to circuit on matrix chart with next highest number (for appropriate symptom). (Scheme 3) If battery voltage is not present, check cigarette fuse. See CIG FUSE CHECK.

CIG Fuse Check

Remove fuse from junction block No. 1. (Scheme 12) Check continuity of fuse. If fuse is okay, check harness or connector between A/C control assembly and battery. Repair as necessary. If fuse is blown, replace fuse, and check for short circuit.

1. Remove A/C control assembly with harness connectors attached. Measure voltage between terminal HR of A/C control assembly 10-pin harness connector and ground. (Scheme 5)
2. Turn ignition on, and measure voltage as indicated in «HEATER MAIN RELAY CIRCUIT SPECIFICATIONS»(/lexus/ls/i-1989-1994/remont/automatic-hvac-system/#ac-heater-system-automatic) table. HEATER MAIN RELAY CIRCUIT SPECIFICATIONS Condition Volts Ignition Switch OFF 0 Ignition Switch ON Blower Switch ON 0 Blower Switch OFF Battery Voltage
3. If voltage is as specified, go to circuit with next highest number on matrix chart (for appropriate symptom). (Scheme 3) If voltage is not as specified, check heater main relay. See HEATER MAIN RELAY TEST.

Heater Main Relay Test

1. Remove heater main relay from junction block No. 2 located in engine compartment. (Scheme 1)and (Scheme 4). Continuity should exist between relay terminals No. 1 and 3 and terminals No. 2 and 4. (Scheme 8) Continuity should not exist between terminals No. 4 and 5.
2. Apply battery voltage to terminal No. 1, and ground terminal No. 3. Continuity should now exist between terminals No. 4 and 5. Ensure continuity no longer exists between terminals No. 2 and 4.
3. If continuity of relay is not as specified, replace heater relay. If continuity is as specified, check heater fuse. See HTR FUSE CHECK.

Remove fuse from junction block No. 1 located below dash, on driver side. (Scheme 12) Check continuity of fuse. If fuse is okay, check harness or connector between A/C control assembly and battery. Repair as necessary. If fuse is blown, replace fuse, and check for short circuit.

Blower Motor Check

1. Remove blower motor. See «BLOWER MOTOR»(/lexus/ls/i-1989-1994/remont/automatic-hvac-system/#ac-heater-system-automatic) under REMOVAL & INSTALLATION. Connect battery voltage to blower motor connector terminal No. 2, and ground terminal No. 1. (Scheme 8)
2. Blower motor should operate smoothly. If blower motor does not operate smoothly, replace blower motor. If blower motor operates smoothly, check blower resistor. See BLOWER RESISTOR TEST.

Blower Resistor Test

1. Disconnect blower resistor connector. Measure resistance between resistor terminals. Resistance should be 1.8 ohms. If resistance is not as specified, replace blower resistor.
2. If resistance is 1.8 ohms, check wiring harness and connectors between battery and blower motor and between blower motor and body ground. Repair or replace as necessary. If wiring harness and connectors are okay, go to circuit with next highest number on matrix chart (for appropriate symptom). (Scheme 3)

Power Transistor Check

1. Remove cooling unit. See «COOLING & BLOWER UNIT»(/lexus/ls/i-1989-1994/remont/automatic-hvac-system/#ac-heater-system-automatic) under REMOVAL & INSTALLATION. Disconnect power transistor connector. Connect battery voltage to terminal No. 2 of connector A25 and terminal No. 2 of connector A26. (Scheme 13)
2. Ground terminal No. 1 of connector A25 through a 12-volt, 1.3-watt test light. If test light does not illuminate, replace power transistor. If test light illuminates, check wiring harness and connectors between A/C control assembly and power transistor.
3. If wiring harness and connectors are damaged, repair or replace as necessary. If wiring harness and connectors are okay, go to circuit with next highest number on matrix chart (for appropriate symptom). (Scheme 3)

Scheme 13

1. Warm engine to normal operating temperature. Perform INDICATOR CHECK. See «RETRIEVING CODES»(/lexus/ls/i-1989-1994/remont/automatic-hvac-system/#ac-heater-system-automatic) under TROUBLE SHOOTING. After system enters DIAGNOSTIC CODE CHECK, press REC switch. (Scheme 2)
2. Press UP switch to display appropriate display codes. See «EXTRA-HIGH RELAY CIRCUIT»(/lexus/ls/i-1989-1994/remont/automatic-hvac-system/#ac-heater-system-automatic) table. If blower operation is as specified, go to circuit with next highest number on matrix chart (for appropriate symptom). (Scheme 3) If blower operation is not as specified, check extra-high relay. See EXTRA-HIGH RELAY TEST.

EXTRA-HIGH RELAY CIRCUIT

Extra-High Relay Test

1. Remove extra-high relay. See «EXTRA-HIGH RELAY»(/lexus/ls/i-1989-1994/remont/automatic-hvac-system/#ac-heater-system-automatic) under REMOVAL & INSTALLATION. Continuity should exist between terminals No. 1 and 3. (Scheme 8) Continuity should not exist between terminals No. 4 and 5.
2. Apply battery voltage to terminal No. 1, and ground terminal No. 3. Ensure continuity now exists between terminals No. 4 and 5. If continuity of relay is not as specified, replace extra-high relay.
3. If continuity is as specified, check wiring harness and connectors between A/C control assembly and extra-high relay and between extra-high relay and battery. Repair or replace as necessary. If wiring harness and connectors are okay, replace A/C control assembly.

1. Warm engine to normal operating temperature. Perform INDICATOR CHECK. See «RETRIEVING CODES»(/lexus/ls/i-1989-1994/remont/automatic-hvac-system/#ac-heater-system-automatic) under TROUBLE SHOOTING. After system enters DIAGNOSTIC CODE CHECK, press REC switch. (Scheme 2)
2. Press UP switch to display appropriate display codes. See «MODE SERVOMOTOR AIRFLOW OPERATION»(/lexus/ls/i-1989-1994/remont/automatic-hvac-system/#ac-heater-system-automatic) table. Ensure airflow is as specified.
3. If mode servomotor airflow is as specified, go to circuit with next highest number on matrix chart (for appropriate symptom). (Scheme 3) If mode servomotor airflow is not as specified, check mode servomotor. See MODE SERVOMOTOR TEST.

MODE SERVOMOTOR AIRFLOW OPERATION

Mode Servomotor Test

1. Remove heater unit. See «HEATER UNIT»(/lexus/ls/i-1989-1994/remont/automatic-hvac-system/#ac-heater-system-automatic) under REMOVAL & INSTALLATION. Apply battery voltage to mode servomotor connector terminal No. 6, and ground terminal No. 7. (Scheme 14)
2. Individually ground terminals No. 1-5 and observe lever operation. See «MODE SERVOMOTOR LEVER OPERATION SPECIFICATIONS»(/lexus/ls/i-1989-1994/remont/automatic-hvac-system/#ac-heater-system-automatic) table. If lever does not function as specified, replace servomotor.
3. If lever functions as specified, check wiring harness and connectors between A/C control assembly and mode servomotor, and between battery, mode servomotor and ground. Repair or replace as necessary. If wiring harness and connectors are okay, replace A/C control assembly.

MODE SERVOMOTOR LEVER OPERATION SPECIFICATIONS

Scheme 14

1. Warm engine to normal operating temperature. Perform INDICATOR CHECK. See «RETRIEVING CODES»(/lexus/ls/i-1989-1994/remont/automatic-hvac-system/#ac-heater-system-automatic) under TROUBLE SHOOTING. After system enters DIAGNOSTIC CODE CHECK, press REC switch. (Scheme 2)
2. Press UP switch to display appropriate display codes. See «MAXIMUM COOL SERVOMOTOR DAMPER OPERATION»(/lexus/ls/i-1989-1994/remont/automatic-hvac-system/#ac-heater-system-automatic) table. Ensure maximum cool damper operates as specified. MAXIMUM COOL SERVOMOTOR DAMPER OPERATION Display Code Maximum Cool Damper Mode 20-21 Open 22 Medium 23-29 Closed
3. If damper operation is as specified, go to circuit with next highest number on matrix chart (for appropriate symptom). (Scheme 3) If damper operation is not as specified, check maximum cool servomotor. See MAXIMUM COOL SERVOMOTOR TEST.

Maximum Cool Servomotor Test

1. Remove heater unit. See «HEATER UNIT»(/lexus/ls/i-1989-1994/remont/automatic-hvac-system/#ac-heater-system-automatic) under REMOVAL & INSTALLATION. Remove maximum cool servomotor. Apply battery voltage to maximum cool servomotor terminal No. 4, and ground terminal No. 5. (Scheme 15)
2. Individually ground terminals No. 1-3 and observe lever operation. See «MAXIMUM COOL SERVOMOTOR LEVER OPERATION»(/lexus/ls/i-1989-1994/remont/automatic-hvac-system/#ac-heater-system-automatic) table. If lever does not function as specified, replace servomotor.
3. If lever functions as specified, check wiring harness and connectors between A/C control assembly and maximum cool servomotor and between battery and maximum cool servomotor. Repair or replace as necessary. If wiring harness and connectors are okay, replace A/C control assembly.

MAXIMUM COOL SERVOMOTOR LEVER OPERATION

Scheme 15

1. Remove A/C control assembly with harness connectors attached. Turn ignition on. Press LO, MED or HI fan speed switch. Measure voltage between ground and A/C I terminal of A/C control assembly 16-pin harness connector. (Scheme 5)
2. With A/C switch in ON position, voltmeter should read battery voltage. With A/C switch in OFF position, voltmeter should read zero volt. If compressor circuit voltage is as specified, check A/C compressor magnetic clutch. See MAGNETIC CLUTCH TEST. If compressor circuit voltage is not as specified, check magnetic clutch circuit voltage. See MAGNETIC CLUTCH CIRCUIT VOLTAGE CHECK.

Magnetic Clutch Test

1. Disconnect magnetic clutch connector. Apply battery voltage to magnetic clutch connector, and ground negative lead. If magnetic clutch is not energized, repair A/C compressor magnetic clutch.
2. If magnetic clutch is energized, check wiring harness and connectors between compressor relay and A/C control assembly. Repair or replace as necessary. If wiring harness and connectors are okay, check A/C pressure switch. See «PRESSURE SWITCH CIRCUIT»(/lexus/ls/i-1989-1994/remont/automatic-hvac-system/#ac-heater-system-automatic) under TESTING.

Magnetic Clutch Circuit Voltage Check

1. Turn ignition on. Press LO, MED or HI fan speed switch. Measure voltage between terminal MGC of A/C control assembly 18-pin harness connector and ground. (Scheme 5)
2. With A/C switch in ON position, voltmeter should read zero volt. Voltmeter should read approximately 5 volts with A/C switch in OFF position. If voltage is as specified, check magnetic clutch relay. See MAGNETIC CLUTCH RELAY CHECK. If voltage is not as specified, go to next step.
3. Disconnect A/C control assembly connector. Turn ignition on. Measure voltage between terminal MGC of A/C control assembly 18-pin harness connector and ground. (Scheme 5)
4. If voltage is approximately 5 volts, check A/C control assembly, and replace as necessary. If voltage is not approximately 5 volts, check wiring harness and connectors between A/C control assembly and engine/transmission ECU. Repair or replace as necessary.
5. If wiring harness and connectors are okay, replace engine/transmission ECU. See «ENGINE/TRANSMISSION ECU»(/lexus/ls/i-1989-1994/remont/automatic-hvac-system/#ac-heater-system-automatic) under REMOVAL & INSTALLATION.

Magnetic Clutch Relay Check

1. Remove magnetic clutch relay from junction block No. 2 in engine compartment. (Scheme 1)and (Scheme 4). Continuity should exist between terminals No. 1 and 3. (Scheme 8) Continuity should not exist between relay terminals No. 2 and 4.
2. Apply battery voltage to relay terminal No. 1, and ground terminal No. 3. Continuity should exist between relay terminals No. 2 and 4. If continuity of relay is not as specified, replace magnetic clutch relay. If continuity is as specified, perform ENGINE/TRANSMISSION ECU CIRCUIT VOLTAGE CHECK.

Engine/Transmission ECU Circuit Voltage Check

1. Remove engine/transmission ECU with harness connectors attached. See «ENGINE/TRANSMISSION ECU»(/lexus/ls/i-1989-1994/remont/automatic-hvac-system/#ac-heater-system-automatic) under REMOVAL & INSTALLATION. Turn ignition on. Press LO, MED or HI fan speed switch. Measure voltage between terminal A/C MG of engine/transmission ECU harness connector and ground. (Scheme 16)
2. With A/C switch in ON position, voltmeter should read approximately 1.3 volts. With A/C switch in OFF position, voltage should be between 1.3 volts and battery voltage. If voltage is not as specified, replace engine/transmission ECU.
3. If voltage is as specified, check wiring harness and connectors between engine/transmission ECU and A/C control assembly. Repair or replace as necessary. If wiring harness and connectors are okay, replace A/C control assembly.

Scheme 16

Pressure Switch Circuit Voltage Check

1. Install manifold gauge set. Turn ignition on. Measure voltage between terminal PSW of A/C control assembly 16-pin harness connector and ground. (Scheme 5) Observe voltage and pressure readings.
2. On low-pressure side of system, voltage should switch from 12 to zero volts as pressure increases beyond 28 psi (2 kg/cm 2 ). On high-pressure side of system, voltage should switch from zero to 12 volts as pressure increases beyond 384 psi (27 kg/cm 2 ).
3. If voltage changes as specified, go to circuit with next highest number on matrix chart (for appropriate symptom). (Scheme 3) If voltage is not as specified, check pressure switch continuity. See PRESSURE SWITCH CONTINUITY CHECK.

Pressure Switch Continuity Check

1. Remove right headlight. Disconnect pressure switch connector. Turn ignition on. Check continuity between switch terminals No. 1 and 4 while varying A/C system pressure. (Scheme 8)
2. On low-pressure side of system, continuity should switch from no continuity to continuity as system pressure increases beyond approximately 28 psi (2 kg/cm 2 ). On high-pressure side of system, continuity should switch from no continuity to continuity as pressure increases beyond approximately 384 psi (27 kg/cm 2 ). If continuity is not as specified, replace pressure switch.
3. If continuity is as specified, check wiring harness and connectors between pressure switch and A/C control assembly for damage and open or short circuits. Repair or replace as necessary. If wiring harness and connectors are okay, replace A/C control assembly.

Tachometer Operation Check

1. Use a test tachometer to ensure tachometer operates normally. If tachometer does not operate normally, check tachometer wiring harness and tachometer. Repair or replace as necessary.
2. If tachometer operates normally, check wiring harness and connectors between ignitor and A/C control assembly. Repair or replace as necessary. If wiring harness and connectors are okay, go to circuit with next highest number on matrix chart (for appropriate symptom). (Scheme 3)

Illumination Inspection

1. Remove A/C control assembly with harness connectors attached. Check voltage between ground and TC and both ILL terminals of A/C control assembly 10-pin harness connector. (Scheme 5)
2. With light-control switch in OFF position, voltage should not exist. With light-control switch in TAIL or HEAD position, battery voltage should exist.
3. Check voltage between ground and terminal REOS of 10-pin connector. Turn light-control rheostat and ensure voltage changes evenly. If voltage changes evenly, inspect clock. See CLOCK INSPECTION. If circuits do not function as specified, replace A/C control assembly.

Clock Inspection

1. Inspect clock. If clock is working, go to next step. If clock is not working, ensure battery voltage is 10-16 volts. If voltage is okay, check DOME fuse. (Scheme 1)and (Scheme 4). If fuse is okay, check wiring harness. Repair or replace as necessary.
2. Check clock error. Allowable error is 2 seconds per day. If clock exceeds allowable error, replace clock along with A/C control panel assembly. If clock is okay, check for sticking clock adjustment button. If button fails to return, replace clock along with A/C control panel assembly.
3. If adjustment button is not sticking, check for 10-16 volts between terminal "B" of A/C control assembly 18-pin harness connector and body ground. (Scheme 5)
4. If voltage is as specified, adjust or replace clock with A/C control panel assembly. If voltage is not as specified, recharge or replace battery. If clock is okay, check defogger switch operation. See DEFOGGER SWITCH OPERATIONAL TEST.

Defogger Switch Operational Test

1. Apply battery voltage to terminal IG of A/C control assembly 18-pin harness connector, and ground terminal GND. (Scheme 5) Connect a 1.4-watt test light between terminal RDFG of A/C control assembly 18-pin connector and battery.
2. Turn defogger switch to ON position. Ensure test light and defogger switch indicator light illuminate. Lights should go off after about 15 minutes. If switch functions as specified, check defogger relay. See DEFOGGER RELAY CHECK. If switch does not function as specified, replace A/C control panel assembly.

Defogger Relay Check

1. Remove defogger relay from junction block No. 1. Ensure continuity exists between relay terminals No. 3 and 4. (Scheme 17) Continuity should not exist between relay terminals No. 1 and 2.
2. Apply battery voltage to relay terminal No. 3, and ground relay terminal No. 4. Ensure continuity exists between terminals No. 1 and 2. If continuity is not as specified, replace defogger relay.

Scheme 17

On-Vehicle Inspection

Cooling fan operates at 2 speeds, depending on coolant temperature and A/C switch position. See COOLING FAN OPERATION table. If cooling fan operation is not as specified, check pressure switch. See PRESSURE SWITCH CHECK.

COOLING FAN OPERATION

Pressure Switch Check

1. Remove right headlight. Disconnect pressure switch connector. Install manifold gauge set. Run engine at approximately 2000 RPM.
2. Connect ohmmeter between terminals No. 2 and 3 of pressure switch. (Scheme 8) Ensure continuity is present when A/C switch is in OFF position (high side pressure should be 142 psi or lower).
3. Turn A/C switch to ON position. Ensure continuity is not present (high side pressure should be 192 psi or higher). If continuity is not as specified, replace pressure switch. If continuity is as specified, check coolant temperature switch. See COOLANT TEMPERATURE SWITCH CHECK.

Coolant Temperature Switch Check

1. Remove coolant (water) temperature switch. (Scheme 1) Place switch in container with water. Heat water. Using an ohmmeter, check continuity between terminals of coolant temperature switch.
2. Continuity should be present when water temperature is less than 181°F (83°C). Continuity should not be present when water temperature is greater than 199°F (93°C). Replace switch if continuity is not as specified. If switch continuity is okay, check cooling fan relays. See COOLING FAN RELAYS CHECK.

Cooling Fan Relays Check

1. Remove left headlight. Remove cover for relay block No. 6. (Scheme 1) Remove cooling fan relays. Using an ohmmeter, check continuity between terminals of relays.
2. On No. 1 and 2 relays, continuity should exist between terminals No. 1 and 2 and terminals No. 3 and 4. (Scheme 18) Apply battery voltage across terminals No. 1 and 2. Continuity should no longer exist between terminals No. 3 and 4.
3. On No. 3 relay, continuity should exist between relay terminals No. 1 and 3 and terminals No. 2 and 4. (Scheme 18) Continuity should not exist between relay terminals No. 4 and 5.
4. Apply battery voltage across relay terminals No. 1 and 3. Ensure continuity now exists between relay terminals No. 4 and 5. Continuity should no longer exist between relay terminals No. 2 and 4.
5. Replace relay No. 1, 2 or 3 if continuity is not as specified. If ALL cooling fan relays are okay, check engine main relay. See ENGINE MAIN RELAY CHECK.

Scheme 18

Engine Main Relay Check

1. Remove engine main relay from junction block No. 2. (Scheme 1) Continuity should exist between relay terminals No. 1 and 3 and terminals No. 2 and 4. See F F (Scheme 18). Continuity should not exist between relay terminals No. 4 and 5.
2. Apply battery voltage across relay terminals No. 1 and 3. Ensure continuity now exists between relay terminals No. 4 and 5.
3. Continuity should no longer exist between terminals No. 2 and 4. Replace relay if continuity is not as specified. If relay is okay, check cooling fan motor operation. See COOLING FAN MOTORS OPERATIONAL CHECK.

Cooling Fan Motors Operational Check

Through an ammeter, connect battery voltage and ground to cooling fan motor connector. Ensure cooling fan rotates smoothly and ammeter reading is 4.2-4.4 amps. Replace cooling fan motor if fan motor does not operate smoothly or current is not as specified.

WATER VALVE

1. Disconnect control cable from water valve. Start engine, and warm it to normal operating temperature. Turn blower switch to ON position. Ensure warm air comes out of vent when water valve lever is moved to WARM position. (Scheme 19)
2. Ensure cooler air comes out of vent when water valve lever is moved to COOL position. (Scheme 19) If operation is not as specified, replace water valve. Install control cable after inspecting.

Scheme 19

REMOVAL & INSTALLATION

Removal

1. Turn ignition switch to LOCK position. Disconnect negative battery cable. Wait 20 SECONDS after ignition switch is turned to LOCK position and negative battery cable is disconnected.
2. Place front wheels in straight-ahead position. Loosen 4 Torx screws from side covers on steering wheel. Loosen Torx screws until groove along screw circumference catches onto screw case.
3. Remove side covers. Pull air bag module out of steering wheel and disconnect air bag wiring connector. DO NOT pull on air bag wiring harness.

Installation

1. Ensure front wheels face straight ahead. Turn spiral cable counterclockwise by hand until resistance is felt. Back off spiral cable 2 1/2 turns and align red reference marks on spiral cable and outer housing.
2. Install steering wheel, and tighten steering wheel nut to 26 ft. lbs. (35 N.m). Connect air bag harness connector. Ensure circumference groove on Torx screws catches onto screw cases.
3. Install air bag module onto steering wheel. Ensure module faces up. Ensure wiring harness does not interfere with, or is pinched by, other moving parts.
4. Install side covers. Tighten Torx screws to 65 INCH lbs. (7.4 N.m). Perform SYSTEM OPERATION CHECK. See AIR BAG SYSTEM SAFETY article in the AIR BAG Section.

1. Start engine, and run it at idle with A/C on for about 10 minutes. Turn engine off, and remove battery. Discharge A/C system using approved refrigerant recovery/recycling equipment.
2. Remove discharge hose and suction hose from compressor. Cap open fittings immediately. Remove drive belt. Remove ground wire bolt from compressor. Remove nut, 3 bolts, bracket and compressor.

1. Install compressor with bracket, nut and 3 bolts. Tighten bolts to 36 ft. lbs. (49 N.m). Tighten nut to 22 ft. lbs. (30 N.m). Install ground wire, and install drive belt.
2. Reconnect discharge and suction hoses to compressor. Tighten fittings to 18 ft. lbs. (24 N.m). Connect magnetic clutch harness connector. Install battery. Evacuate and charge A/C system. Check A/C system for leaks and proper operation.

Remove upper shift console panel. Remove ashtray. Remove register from above radio. Remove 4 screws and radio along with A/C control assembly. Remove 4 screws, and pry apart side claws. Remove A/C control assembly from radio. (Scheme 1) To install, reverse removal procedure.

Remove clip and sensor from right side bumper reinforcement. Disconnect harness connector. To install, reverse removal procedure.

1. Set air inlet mode to FRS (fresh). Remove undercover on right side of instrument panel. Disconnect wiring connectors, and remove connector bracket from cooling unit. Remove front passenger-door scuff plate.
2. Pull back cowl-side portion of carpet. Disconnect control lever shaft from blower case. Remove screws and blower lower case. Disconnect wiring connectors, and remove 3 screws. Remove blower motor. To install, reverse removal procedure.

Remove undercover on right side of instrument panel. Disconnect wiring harness connectors. Remove 2 screws and connector bracket from cooling and blower unit. Remove screws and blower resistor from cooling and blower unit. (Scheme 20) Disconnect harness connector. To install, reverse removal procedure.

1. Remove front parking lights. Remove headlights. Remove engine undercover. Remove lower wind guide. Remove fender liner from bumper. Remove bumper and bumper retainer. Remove bumper reinforcement.
2. Remove horns. Disconnect and remove electric cooling fans. Remove center brace. Discharge A/C system using approved refrigerant recovery/recycling equipment.
3. Remove bolts. Disconnect liquid and discharge tubes from condenser. Remove suction tube. Remove 2 nuts, and remove condenser.

1. To install, reverse removal procedure. Tighten suction tube fitting to 24 ft. lbs. (33 N.m). Tighten discharge and liquid tube fittings to 84 INCH lbs. (10 N.m).
2. If condenser is replaced, add 1.4-1.7 ozs. of compressor oil to compressor. Evacuate and charge A/C system. Check A/C system for leaks and proper operation.

1. Disconnect negative battery cable. Discharge A/C system using approved refrigerant recovery/recycling equipment. Remove cruise control actuator from engine compartment. Disconnect equalizer tubes from cooling and blower unit. Remove liquid and suction tubes.
2. Remove cover plate on firewall. Remove drain hose clamp from front-side member. Remove heater to register No. 4 and 5 ducts. Remove glove box assembly. Disconnect two wiring harness connectors, and remove mirror-control ECU from glove box opening.
3. Remove bolts and bracket from cooling and blower unit. Disconnect wiring harness connectors. Remove 4 nuts and 2 screws. Remove cooling and blower unit.

Disassembly

1. Remove air inlet servomotor assembly, power transistor, extra-high relay and blower resistor from cooling and blower unit. (Scheme 20) Remove A/C wire harness. Remove 8 screws, and separate upper and lower cases. Pull evaporator sensor from evaporator fins.
2. Remove 2 hex bolts, and separate evaporator and expansion valve. Disconnect shaft from control lever. Remove blower motor lower case. Remove blower motor. Inspect fins for blockage and damage.

Scheme 20

Reassembly

To reassemble, reverse disassembly procedure. Tighten expansion valve-to-evaporator bolt to 48 INCH lbs. (5.5 N.m). Connect shaft and control lever of blower lower case by turning lever counterclockwise and pulling shaft down.

To install, reverse removal procedure. Tighten tube fittings to 84 INCH lbs. (10 N.m). If evaporator is replaced, add 1.4-1.7 ozs. of compressor oil to compressor. Evacuate and charge A/C system. Check A/C system for leaks and proper operation.

1. Remove headlights. Remove front bumper. Remove horns. Disconnect harness connectors of fan motor. Disconnect wire from brackets. Remove each 3-bolt set, and remove cooling fan.
2. Remove 4 bolts and fan cover. Remove nut securing fan, and remove fan. Disconnect fan motor harness connector from bracket. Remove 3 screws, and remove fan motor. To install, reverse removal procedure.

Remove glove box, right undercover of instrument panel and lower left pad of instrument panel. Disconnect harness connectors from engine/transmission ECU. Remove engine/transmission ECU. To install, reverse removal procedure.

Remove cooling and blower unit. See COOLING & BLOWER UNIT under REMOVAL & INSTALLATION. Remove evaporator sensor from cooling and blower unit. To install, reverse removal procedure.

Remove undercover on right side of instrument panel. Disconnect wiring harness connectors. Remove 2 screws and connector bracket from cooling and blower unit. Remove screw and extra-high relay from cooling and blower unit. (Scheme 20) Disconnect harness connector. To install, reverse removal procedure.

1. Disconnect negative battery cable. Drain engine coolant from radiator and engine-drain cocks. Draining coolant completely from engine is not necessary.
2. Remove water valve. See «WATER VALVE»(/lexus/ls/i-1989-1994/remont/automatic-hvac-system/#ac-heater-system-automatic) under REMOVAL & INSTALLATION. Remove cooling and blower unit. See «COOLING & BLOWER»(/lexus/ls/i-1989-1994/remont/automatic-hvac-system/#ac-heater-system-automatic) UNIT under REMOVAL & INSTALLATION. Disconnect water hose from engine.
3. Remove the insulator retainer. Remove safety pad. See «SAFETY PAD (DASHBOARD)»(/lexus/ls/i-1989-1994/remont/automatic-hvac-system/#ac-heater-system-automatic) under REMOVAL & INSTALLATION. Disconnect and remove rear vent ducts. Disconnect and remove heater ducts. Remove duct between heater and upper center registers. Remove 4 nuts, and remove heater unit.

1. Disconnect and remove mode servomotor. (Scheme 21) Remove aspirator. Remove packing, plate and clamp from heater radiator. Remove radiator. Remove coolant temperature sensor and No. 1 air duct.
2. Remove control cable from air mix servomotor assembly. To remove maximum cool servomotor and air mix servomotor assembly, use screwdriver to pry loose 2 clips and remove control plate(s). Remove both servomotors. Disconnect shaft, and remove vent air duct.

Scheme 21

To reassemble, reverse disassembly procedure. Connect shaft and damper control plate of center vent, with control plate of defrost and damper control plate of center vent turned fully counterclockwise.

To install, reverse removal procedure. After installing cooling and blower unit, evacuate and charge A/C system. After installation is complete, check A/C system for leaks and proper operation.

1. Remove undercover on right side of instrument panel. Remove glove box. Remove lower right pad. Remove glove box door. Remove Anti-Lock Brake System (ABS) control unit, and disconnect wiring harness connectors.
2. Remove air duct from heater to passenger-side registers. Remove screw and plate from cooling and blower unit. Disconnect 2 harness connectors. Remove screw and power transistor from cooling and blower unit. (Scheme 20) To install, reverse removal procedure.

Discharge A/C system using approved refrigerant recovery/recycling equipment. Remove right headlight. Disconnect pressure switch harness connector. Remove pressure switch from liquid tube.

Install pressure switch to liquid tube. Tighten fittings to 84 INCH lbs. (10 N.m). Connect pressure switch harness connector. Evacuate and charge A/C system. Check A/C system for leaks and proper operation. Install headlight.

Remove right headlight. Discharge A/C system using approved refrigerant recovery/recycling equipment. Disconnect tubes from receiver-drier. Remove receiver-drier from holder.

To install, reverse removal procedure. If receiver-drier is replaced, add 0.7 oz. of compressor oil to compressor. Evacuate and charge A/C system. Check A/C system for leaks and proper operation. Install headlight.

1. Remove undercover on left side of instrument panel. Remove hood-release lever. Disconnect release cable from lever. Remove key cylinder pad from steering column using a screwdriver.
2. Remove lower left pad. Disconnect harness connector to room temperature sensor. Remove screw and room temperature sensor from lower pad. To install, reverse removal procedure.

1. Tilt down and pull out steering wheel. Ensure ignition is off. Disconnect negative battery cable. Wait at least 20 seconds before continuing. Remove rear passenger-assist grips. Remove anchor bolt of front seat belt. Remove right and left front pillar garnish.
2. Disable the system and remove the air bag module. See «AIR BAG MODULE»(/lexus/ls/i-1989-1994/remont/automatic-hvac-system/#ac-heater-system-automatic) under REMOVAL & INSTALLATION. Remove steering wheel using steering wheel puller. Remove steering column covers. Remove upper console panel and front ashtray. Remove lower console cover and lower console box. Remove cup holder and console box.
3. Remove hood-release lever. Remove undercover of instrument panel. Remove key cylinder pad and left lower pad. Remove parking brake lever. Disconnect and remove outer mirror switch assembly.
4. Remove and disconnect cluster finish panel and instrument cluster. Remove registers. Remove radio with A/C control assembly. Remove glove box and door. Remove right lower pad. Remove Anti-Lock Brake System (ABS) control unit.
5. Remove heater ducts. On driver side, loosen lock bolt and disconnect junction block. Remove 3 clips at floor carpet using clip remover. Remove screws and combination switch.
6. On passenger side, disconnect wiring harness connectors under safety pad. Remove bolt and bond cable. Remove 3 carpet clips using a clip remover. Remove one nut and 9 bolts securing safety pad. Remove safety pad. To install, reverse removal procedure.

Disconnect solar sensor harness connector. Remove 8 screws, and remove defroster front nozzle with side defroster nozzle ducts attached. Push out solar sensor from rear of safety pad. Loosen 7 clips, and remove nozzle garnish. To install, reverse removal procedure.

Unlock clamp, and remove control cable from water valve. Loosen hose band, and remove water hose. Move spring clip, and disconnect water valve-to-heater unit hose. Remove 2 nuts, and remove water valve.

1. Install hoses to water valve and heater unit. Install hose clamps. Install water valve, and tighten nuts. Turn ignition on.
2. Set blower switch to ON position. Set TEMP switch to maximum cool position. Set water valve lever to maximum cool position, and install control cable. (Scheme 22) Lock cable clamp.

Scheme 22

Automatic A/C-Heater System Wiring Diagram (1 of 2). Scheme 23

Automatic A/C-Heater System Wiring Diagram (2 of 2). Scheme 24

See also:
• CODE 22 - COMPRESSOR LOCK SENSOR CIRCUIT