A/c-Heater System - Automatic: Other Lexus LX J80

SYSTEM CONTROLS

A/C-heater functions are controlled by push-button controls, A/C auto switch, A/C on-off switch, and sliding temperature control lever. (Scheme 9) A/C controls operate air supply selection (fresh or recirculated air), mode selection, and temperature selection and blower speeds.

Scheme 9

WATER VALVE CONTROL CABLE

Turn ignition on. Set blower switch to any position except off. Set temperature control lever to cool position. Remove cable retaining clamp. Ensure water valve is in full cool position. Install control cable, and snap retaining clamp into position.

BLOWER MOTOR DOES NOT OPERATE

Check for blown fuse or faulty heater relay. Check for faulty blower motor or A/C system amplifier.

CANNOT CONTROL BLOWER MOTOR

Check for faulty A/C-heater control panel, blower high relay, blower resistor, power transistor or A/C system amplifier.

INSUFFICIENT AIR VELOCITY

Check for faulty heater relay, blower motor or blower resistor. Check evaporator fins or heater core fins for blockage.

NO COOL AIR COMES OUT

Check for incorrect refrigerant charge and for loose or broken A/C drive belt. Check for faulty A/C compressor clutch relay, pressure switch, compressor clutch, compressor, or faulty A/C-heater control assembly. Check water valve control cable adjustment. Check for faulty A/C amplifier, A/C system amplifier, air mix servomotor, servomotor amplifier or engine coolant temperature cut relay. Check for faulty coolant temperature cut switch, evaporator temperature sensor, engine coolant temperature sensor, in-vehicle temperature sensor, ambient temperature sensor or solar sensor.

NO WARM AIR COMES OUT

Check water valve control cable adjustment. Check for faulty A/C-heater control assembly, air mix servomotor, servomotor amplifier or engine coolant temperature sensor.

OUTPUT AIR DIFFERENT FROM SET TEMPERATURE

Check for incorrect refrigerant charge and for loose or broken A/C drive belt. Inspect A/C system performance. See A/C SYSTEM PERFORMANCE under TESTING. Check water valve control cable adjustment. Check for faulty solar sensor, in-vehicle sensor, evaporator temperature sensor or engine coolant temperature sensor. Check for faulty air mix servomotor or air inlet servomotor. Check condenser fins for blockage or damage. Check condenser fittings and receiver fittings for leaks. Check evaporator fins for blockage. Check for faulty expansion valve. Check heater core fins for blockage. Check for faulty A/C-heater control assembly, A/C system amplifier or A/C amplifier.

CANNOT CONTROL TEMPERATURE (MAXIMUM COLD OR HOT ONLY)

Check for faulty air mix servomotor, servomotor amplifier, A/C-heater control assembly, A/C amplifier or A/C system amplifier.

CANNOT CONTROL AIR INPUT OR OUTPUT

Check for faulty air inlet servomotor, air outlet servomotor, A/C-heater control assembly or A/C amplifier.

IDLE DOES NOT CHANGE WITH A/C ON

Check for faulty compressor clutch, A/C-heater control assembly,A/C system amplifier or A/C amplifier.

A/C SYSTEM PERFORMANCE

1. Park vehicle out of direct sunlight. Install manifold gauge set. Set A/C controls to recirculated air position and 86-95°F (30-35°C) temperature setting. Start engine and allow to run at 1500 RPM.
2. Set blower on high speed and temperature control switch to maximum cooling. Verify high side and low side pressures are within specification. See «A/C-HEATER SYSTEMS SPECIFICATIONS»(ref-125179-S12789377292001100400000) table at beginning of article.

A/C AMPLIFIER

Remove glove compartment assembly. Disconnect A/C amplifier connector. A/C amplifier is located on front of A/C cooling unit (evaporator housing). see scheme 1 Test wire harness side of connector. (Scheme 10) Test circuits as specified in A/C AMPLIFIER CIRCUIT TEST table. If circuits DO NOT test as specified, repair as necessary.

Scheme 10

A/C AMPLIFIER CIRCUIT TEST

A/C SYSTEM AMPLIFIER

1. Remove instrument panel safety pad. See «INSTRUMENT PANEL»(ref-125179-S37932349742001100400000) under REMOVAL & INSTALLATION. Disconnect A/C system amplifier connector. A/C system amplifier is located behind center of instrument panel. see scheme 1 Test wire harness side of connector. (Scheme 11)
2. Test circuits as specified in A/C SYSTEM AMPLIFIER CIRCUIT TEST table. If circuits DO NOT test as specified, repair as necessary. If circuits test as specified, replace A/C system amplifier.

Scheme 11

A/C SYSTEM AMPLIFIER CIRCUIT TEST

AUTOMATIC A/C AMPLIFIER

1. Disconnect automatic A/C amplifier connector. Automatic A/C amplifier is located behind left side of instrument panel. see scheme 1 Test wire harness side of connector. (Scheme 12) Test circuits as specified in «AUTOMATIC A/C AMPLIFIER CIRCUIT TEST (CONNECTOR UNPLUGGED)»(ref-125179-S06067041132001100400000) table. If circuits DO NOT test as specified, repair as necessary. If circuits test as specified, go to next step.
2. Reconnect automatic A/C amplifier connector. Backprobe circuits specified in «AUTOMATIC A/C AMPLIFIER CIRCUIT TEST (CONNECTOR PLUGGED IN)»(ref-125179-S13525050882001100400000) table. If circuits DO NOT test as specified, repair as necessary. If circuits test as specified, replace automatic A/C amplifier.

Scheme 12

AUTOMATIC A/C AMPLIFIER CIRCUIT TEST (CONNECTOR UNPLUGGED)

AUTOMATIC A/C AMPLIFIER CIRCUIT TEST (CONNECTOR PLUGGED IN)

AIR INLET SERVOMOTOR

1. Remove glove box assembly. Remove air inlet servomotor. Connect battery voltage to servomotor terminal No. 1. (Scheme 13) Connect servomotor terminal No. 2 to ground.
2. Servomotor lever should move smoothly to fresh air position. Connect battery voltage to servomotor terminal No. 1. Connect servomotor terminal No. 3 to ground. Servomotor lever should move smoothly to recirculate position. If operation is not as specified, replace servomotor.

Scheme 13

AIR MIX SERVOMOTOR

1. Remove instrument panel. See «INSTRUMENT PANEL»(ref-125179-S37932349742001100400000) under REMOVAL & INSTALLATION. Remove air mix servomotor. Connect battery voltage to servomotor terminal No. 5. (Scheme 14) Connect servomotor terminal No. 4 to ground.
2. Servomotor lever should move smoothly to cool air position. Transpose power leads. Servomotor lever should move smoothly to hot air position. If operation is not as specified, replace servomotor. If operation is as specified, go to next step.
3. Measure resistance between servomotor terminals No. 1 and 3. If resistance is not about 6000 ohms, replace servomotor. If resistance is as specified, set servomotor lever to hot position. While rotating servomotor lever from hot position to cool position, measure resistance between terminals No. 2 and 3. Replace servomotor if resistance does not increase from 1200 ohms to 4800 ohms while rotating lever from hot position to cool position.

Scheme 14

AIR OUTLET SERVOMOTOR

1. Remove lower left panel from instrument panel. Remove air duct. Remove air outlet servomotor. Connect battery voltage to servomotor terminal No. 5. (Scheme 15) Connect terminal No. 6 to ground.
2. Using jumper wire, ground specified servomotor terminals, and ensure lever move to appropriate position. See «AIR OUTLET»(ref-125179-S13860050362001100400000) SERVOMOTOR TEST table. If lever does not move as specified, replace servomotor.

AIR OUTLET SERVOMOTOR TEST

Scheme 15

AMBIENT TEMPERATURE SENSOR

Unplug sensor connector. Remove bolt and sensor. see scheme 1 Measure resistance between sensor terminals. If resistance is not 1615-1785 ohms with sensor at 77°F (25°C), replace ambient temperature sensor.

COMPRESSOR CLUTCH

Inspect pressure plate and rotor for signs of oil contamination. Check clutch bearing for noisy operation and grease leakage. Disconnect compressor clutch connector. Apply battery voltage to compressor clutch connector terminal. Connect negative battery lead to ground. Ensure compressor clutch is energized. If compressor clutch is not energized, replace compressor clutch.

COMPRESSOR CLUTCH RELAY

Remove compressor clutch relay. Ensure continuity is present between relay terminals No. 1 and 3. (Scheme 16) Ensure continuity is not present between terminals No. 2 and 4. Connect battery voltage and ground between terminals No. 1 and 3. If continuity is not present between relay terminals No. 2 and 4 with battery voltage connected, replace compressor clutch relay.

Scheme 16

COOLANT (WATER) TEMPERATURE SENSOR

Remove instrument panel safety pad. See INSTRUMENT PANEL under REMOVAL & INSTALLATION. Remove clamp, disconnect sensor connector, and remove sensor. Place sensor and thermometer in water. Measure resistance between sensor terminals while varying water temperature. If resistance is not as specified, replace coolant temperature sensor. See COOLANT TEMPERATURE SENSOR RESISTANCE SPECIFICATIONS table.

COOLANT TEMPERATURE SENSOR RESISTANCE SPECIFICATIONS

DUAL-PRESSURE SWITCH

Install manifold gauge set. Disconnect dual-pressure switch 4-pin connector, located near left front of engine compartment. (Scheme 17) Start and operate engine at approximately 1500 RPM. As system pressure changes, check continuity between switch terminal No. 1 (Blue/Red wire) and No. 2 (Yellow/Red). See DUAL-PRESSURE SWITCH TEST table. Replace switch if it does not function as specified.

DUAL-PRESSURE SWITCH TEST

Scheme 17

ENGINE COOLANT TEMPERATURE CUT RELAY

Remove engine coolant temperature cut relay. Ensure continuity is present between relay terminals No. 1 and 3. (Scheme 16) Ensure continuity is not present between terminals No. 2 and 4. Connect battery voltage and ground between terminals No. 1 and 3. If continuity is not present between relay terminals No. 2 and 4 with battery voltage connected, replace compressor clutch relay.

EXPANSION VALVE

Ensure A/C system is fully charged. Install manifold gauge set. Start engine and run for 5 minutes. Ensure high pressure reading is 199-228 psi (14-16 kg/cm 2 ). If low pressure reading drops to 0 psi (0 kg/cm 2 ), expansion valve is faulty and must be replaced.

IN-VEHICLE TEMPERATURE SENSOR

Remove center cluster finish panel. Disconnect aspirator hose from sensor. Remove sensor, and unplug connector. see scheme 1 Measure resistance between sensor terminals. If resistance is not 1615-1785 ohms, replace in-vehicle temperature sensor.

MAIN BLOWER MOTOR

Remove main blower motor. See MAIN BLOWER MOTOR under REMOVAL & INSTALLATION. Connect positive battery lead to blower motor terminal No. 2 (Blue/Red wire). Connect blower motor terminal No. 1 (Blue/Yellow wire) to ground. Ensure blower motor operates smoothly. Replace blower motor if operation is not as specified.

MAIN BLOWER MOTOR HIGH (HI) RELAY

Remove main blower motor high (hi) relay. Ensure continuity is present between relay terminals No. 3 and 4. (Scheme 18) Ensure continuity is not present between terminals No. 1 and 2. Connect battery voltage and ground between terminals No. 3 and 4. If continuity is not present between relay terminals No. 1 and 2 with battery voltage connected, replace main blower hi relay.

Scheme 18

MAIN BLOWER MOTOR RESISTOR

Remove and disassemble evaporator assembly. See EVAPORATOR ASSEMBLY under REMOVAL & INSTALLATION. Remove blower motor resistor. see scheme 16 Measure resistance between resistor terminals. If resistance is not 1.8-2.2 ohms, replace main blower motor resistor.

MAIN HEATER RELAY

Remove main heater relay. See WIRING DIAGRAMS. Ensure continuity is present between relay terminals No. 1 and 3 and between terminals No. 2 and 4. (Scheme 19) Ensure continuity is not present between terminals No. 4 and 5. Connect battery voltage and ground between terminals No. 1 and 3. If continuity is not present between relay terminals No. 4 and 5 with battery voltage connected, replace main heater relay.

Scheme 19

POWER TRANSISTOR

Remove power transistor. see scheme 16 Connect a 3.4-watt test bulb in series with positive battery terminal and terminal No. 1 of power transistor. (Scheme 20) Connect a 120-ohm resistor in series with positive battery terminal and terminal No. 3 of power transistor. Connect terminal No. 2 to ground. Replace power transistor if test bulb does not glow when terminal No. 2 is grounded.

Scheme 20

REAR HEATER BLOWER MOTOR

Disconnect rear heater blower motor connector. Using jumper wires, connect battery voltage to terminal No. 1 (Blue wire) and connect terminal No. 3 (Blue/Black wire) to ground. Ensure rear heater blower motor operates smoothly. Replace blower motor if operation is not as specified.

REAR HEATER BLOWER MOTOR RESISTOR

Disconnect negative battery cable, and wait at least 90 seconds. Remove front passenger's seat. Remove rear heater blower motor resistor. Check continuity between terminals No. 1 (Blue wire), No. 2 (Blue/Yellow wire) and No. 3 (Blue/Black wire) of rear heater blower motor resistor. Ensure continuity exists among resistor terminals. Replace rear heater blower motor resistor if continuity is not as specified.

REAR HEATER RELAY

1. Disconnect negative battery cable and wait at least 90 seconds. Remove front passenger's seat. Remove rear heater relay. Ensure continuity exists between relay terminals No 2 and 6, and between terminals No. 1 and 3.
2. Using jumper wires, connect battery positive and negative leads between relay terminals No. 2 and 6. Ensure continuity exists between relay terminals No. 1 and 4. If continuity is not as specified, replace rear heater relay.

REAR HEATER BLOWER SWITCH

1. Disconnect negative battery cable, and wait at least 90 seconds. Remove instrument cluster finish center panel and A/C-heater control assembly. Remove rear heater blower switch.
2. Using jumper wires, connect battery positive lead to terminal No. 5 (Yellow wire) and negative lead to terminal No. 1 (White/Black wire) of rear heater switch. Press each rear heater blower switch in, and ensure appropriate indicator lights up. If indicator(s) DO NOT light up, replace rear heater blower switch. If indicators light up, disconnect jumper wires and go to next step.
3. Check continuity between switch terminals. Continuity should exist between terminals No. 3 and 6 (switch illumination). When switch is in LO position, continuity should exist between terminals No. 1 (White/Black wire) and No. 2 (Blue/Yellow wire).
4. When switch is in HI position, continuity should exist between terminals No. 1 (White/Black wire) and No. 4 (Blue/Black wire). When switch is in off position, continuity should not exist between any terminals. If continuity is not as specified, replace rear heater blower switch.

SOLAR SENSOR

1. Remove instrument panel safety pad. See «INSTRUMENT PANEL»(ref-125179-S37932349742001100400000) under REMOVAL & INSTALLATION. Remove solar sensor from safety pad. Cover sensor with cloth, and check continuity between sensor terminals. Continuity should not exist. If continuity is as specified, go to next step. Replace sensor if continuity is not as specified.
2. Remove cloth from sensor and subject sensor to bright light. Continuity should now exist between sensor terminals. If continuity is as specified, sensor is okay. If continuity is not as specified, replace sensor.

THERMISTOR

1. Disconnect negative battery cable, and wait at least 90 seconds. Remove lower trim panel and glove box. Locate thermistor 4-pin connector.
2. Measure resistance between terminals No. 1 (Red/Green wire) and No. 3 (Green wire), and between terminals No. 2 (White/Blue wire) and No. 4 (Gray/Black wire).
3. Resistance should be 1500 ohms at 77°F (25°C). If resistance is not within specification, replace thermistor. If resistance is as specified, go to next step.
4. Remove evaporator case. See «EVAPORATOR ASSEMBLY»(ref-125179-S25555570242001100400000) under REMOVAL & INSTALLATION. Disassemble evaporator case, and remove thermistor. Submerge thermistor at least 3.94" deep in cold water. (Scheme 21)
5. Place thermometer in water, and measure thermistor resistance at various temperatures. Use ice or hot water to vary water temperature. If readings are not within specification, replace thermistor. See «THERMISTOR RESISTANCE VALUES»(ref-125179-S30622807932001100400000) table.

THERMISTOR RESISTANCE VALUES

Scheme 21

REAR HEATER BLOWER MOTOR, REAR HEATER BLOWER MOTOR RESISTOR

& REAR HEATER RELAY