A/c-Heater System - Automatic: Other Nissan Pathfinder II

A/C Switch

With engine running and fan switch set to desired fan speed, press A/C switch to turn on A/C system. A/C indicator light will illuminate. Press A/C switch again to turn off A/C system. (Scheme 2)

Mode Control Knob

Mode control knob allows selection of airflow outlet. (Scheme 2) When mode knob is set to defrost or foot/defrost, the intake door is set to outside air position.

Recirculation Switch

With recirculation switch off, outside air is drawn into passenger compartment. With recirculation switch on, interior air is recirculated inside vehicle. (Scheme 2)

Temperature Control Knob

Temperature control knob allows temperature of outlet air to be adjusted. (Scheme 2)

Scheme 2

A/C COMPRESSOR CLUTCH CONTROL

With A/C switch on, variable displacement compressor runs continuously under normal operating conditions. Engine Control Module (ECM) will turn compressor on or off based on signal from throttle position sensor.

AIR MIX DOOR CONTROL SYSTEM

The auto amplifier receives input from temperature control knob, in-vehicle temperature sensor, sunload sensor, thermal transmitter and ambient temperature sensor. Auto amplifier monitors these sensor inputs and calculates desired air mix door position to achieve desired temperature setting.

If temperature setting is set at 77°F (25°C), under no sunload condition, ambient and in-vehicle temperatures are 50°F (10°C), air mix door will initially set in full hot position. In-vehicle temperature will increase and when objective temperature of 77°F (25°C) is reached, air mix will shift incrementally to cold position and stay.

AMBIENT TEMPERATURE SENSOR

Ambient sensor is mounted on radiator support center brace. (Scheme 3) Ambient sensor detects ambient temperature. It converts the temperature into a resistance value which is sent to the auto amplifier.

If auto amplifier detects an abrupt ambient temperature change, it will gradually adjust temperature until desired setting is reached. This is done by ambient temperature sensor processing circuit (integrated in the auto amplifier) retarding the auto amplifier function, only allowing the auto amplifier to recognize an ambient temperature increase of 0.4°F (0.2°C) per 100 seconds.

If, for example, the vehicle is stopped in traffic after traveling at highway speeds, ambient temperature sensor will detect high ambient temperature due to heat radiating from radiator. To prevent an unpleasant change in A/C operation from this sudden change in ambient temperature, ambient temperature input process will gradually adjust the temperature.

Scheme 3

ASPIRATOR

The aspirator is located in front of heater unit. It produces vacuum due to air discharged from heater unit, continuously taking compartment air in aspirator and drawing into the in-vehicle temperature sensor.

AUTO AMPLIFIER

The auto amplifier has a built-in microcomputer that processes information from various sensors (sunload, in-vehicle temperature and ambient temperature) and A/C-heater control panel. (Scheme 4) It controls air mix door motor, fan motor and compressor operation.

Scheme 4

FAN SPEED CONTROL SYSTEM

Fan speed control system determines airflow volume. With fan control knob in the AUTO position, fan speed is automatically controlled by signals sent to fan control amplifier by auto amplifier. The signals will very depending on Potentiometer Balance Resistor (PBR), ambient temperature, in-vehicle temperature, amount of sunload, selected temperature and A/C switch signals. Fan speed can also be controlled by manual operation of knob. (Scheme 2) Blower motor applied voltage ranges from about 5 to 12 volts.

When temperature setting is at 77°F (25°C) under no sunload condition, ambient temperature at 14°F (-10°C), and in-vehicle temperature at 50°F (10°C), voltage at blower motor will be 12 volts. When ambient temperature changes to 86°F (30°C), and in-vehicle temperature changes to 77°F (25°C), voltage at blower motor will go to 5 volts.

IN-VEHICLE TEMPERATURE SENSOR

In-vehicle temperature sensor is mounted to lower instrument panel cover. (Scheme 4) Passenger compartment air is drawn into in-vehicle temperature sensor through an aspirator. In-vehicle temperature sensor converts temperature variations to a resistance value. Resistance value is then sent to auto amplifier.

POTENTIOMETER BALANCE RESISTOR (PBR)

Built into air mix door motor assembly, PBR sensor measures opening angle of air mix door.

POTENTIOMETER TEMPERATURE CONTROL (PTC)

PTC is built into A/C-heater control panel. (Scheme 4) PTC has a variable resistor connected to temperature control knob. Resistance value varies based on temperature selected.

STARTING FAN SPEED CONTROL

In all mode positions except vent and defrost, during a cold start condition (coolant temperature below 122°F (50°C)), blower will not operate for up to 126 seconds. The exact start delay time varies depending on ambient and engine coolant temperature. After delay, blower will operate at low speed until engine coolant temperature increases to above 131°F (55°C).

SUNLOAD SENSOR

Sunload sensor is located on center defroster grille. (Scheme 4) It detects sunload using a photo diode. This sunload is converted into a current value, which is input into auto amplifier.

If auto amplifier detects an abrupt change in sunload through the sunload sensor, sunload input processing circuit will vary input to auto amplifier.

AIR MIX DOOR

1. Install air mix door motor on heater unit, and connect wiring harness. Set air temperature control lever at 65°F (18°C) setting and air mix door motor at full cold position.
2. Manually move air mix door lever to full cold position and connect lever to rod holder. (Scheme 5) Move temperature control lever to 85°F (32°C) setting. Ensure air mix door moves from full cold position to full hot position.

Scheme 5

HEATER VALVE CONTROL ROD

Push air mix door lever in direction of arrow. (Scheme 6) Pull heater valve control rod in direction of arrow to obtain.08" (2.0 mm) clearance between ends of rod and link lever. (Scheme 6) Connect rod to door lever. Check operation of heater control valve.

Scheme 6

INTAKE DOOR

Connect intake door motor wiring harness connector. Turn ignition switch to ACC position. Turn recirculation switch off. Set intake door link to fresh air setting. Install intake door motor on intake unit. (Scheme 7) Ensure intake door operates properly when recirculation switch is turned on and off.

Scheme 7

MODE DOOR

Turn mode control knob to defrost position. Manually move side link, and hold mode door in defrost position. Pull cable cover away from side link and secure with clip. (Scheme 8) Ensure mode door operates properly after connecting cable.

Scheme 8

A/C COMPRESSOR CLUTCH DOES NOT ENGAGE

1. Start engine. Set blower speed to high. Push A/C switch on. Ensure A/C switch illuminates and compressor clutch engages. If compressor clutch does not disengage, check compressor belt tension. See «SPECIFICATIONS»(ref-349-S23988023142000030800000) . Adjust or replace compressor belt. If belt is okay, go to next step.
2. Check A/C refrigerant pressure. See «A/C SYSTEM PERFORMANCE»(ref-349-S32227478592000030800000) under TESTING. If A/C refrigerant pressure is correct, check A/C compressor clutch circuit. See «A/C COMPRESSOR CLUTCH CIRCUIT»(ref-349-S04019800432000030800000) under TESTING.
3. If symptom still persists, perform a system operational check. See «OPERATIONAL CHECK»(ref-349-S23179882482000030800000) . If no other symptom exists, replace auto amplifier.

A/C SYSTEM MALFUNCTIONING

Start engine. Set blower speed to high. Push A/C switch on. Ensure A/C switch illuminates and compressor clutch engages. If compressor clutch does not disengage, check auto amplifier power supply and ground circuits. See AUTO AMPLIFIER POWER SUPPLY & GROUND CIRCUIT CHECK under TESTING. If auto amplifier power supply and ground circuits are okay, replace auto amplifier.

AIR MIX DOOR MALFUNCTION

1. Start engine. Rotate blower control switch to high. Turn A/C on. Turn temperature knob to 65°F (18°C). Check for cold air at discharge air outlets. Select foot mode. Move temperature control knob to 85°F (30°C). Check for hot air at discharge air outlets. If system functions as specified, system is okay at this time. If system does not function as specified, go to next step.
2. Check air mix door operation. Check air mix door adjustment. See «AIR MIX DOOR»(ref-349-S09585122422000030800000) under ADJUSTMENTS. If adjustment is okay, check air mix door motor operation. See «AIR MIX DOOR MOTOR & POTENTIOMETER BALANCE RESISTOR (PBR)»(ref-349-S34378182882000030800000) under TESTING. If air mix door motor operation is okay, check air mix door motor circuit. See «AIR MIX DOOR MOTOR CIRCUIT»(ref-349-S18747533052000030800000) under TESTING. If air mix door operation is okay, go to next step.
3. If symptom still persists, perform a system operational check. See «OPERATIONAL CHECK»(ref-349-S23179882482000030800000) . If no other symptom exists, replace auto amplifier.

AIR OUTLET DOES NOT CHANGE

1. Turn ignition and blower switch on. Rotate mode control switch. If air does not come out of correct outlet, or if air distribution ratio is not as specified, adjust mode control cable. See «AIR DISTRIBUTION RATIOS»(ref-349-S22622031312000030800000) table. See «MODE DOOR»(ref-349-S20592831322000030800000) under ADJUSTMENTS.
2. If air comes out of correct duct and air distribution ratio is as specified, no problem is indicated at this time. If, after adjusting mode control cable, symptom still persists, perform a system operational check and check for other symptoms. See «OPERATIONAL CHECK»(ref-349-S23179882482000030800000) .

AIR DISTRIBUTION RATIOS

AIR OUTLET DOES NOT CHANGE BETWEEN VENT, BI-LEVEL OR FOOT MODE

1. Depress recirculation switch. Ensure recirculation switch illuminates. Listen for intake door position to change (slight change in sound). Ensure recirculation switch turns off when mode position switch is rotated to defrost position or foot/defrost position.
2. If system functions as specified, system is okay at this time. If system does not function as specified, perform intake door motor circuit test. See «INTAKE DOOR MOTOR CIRCUIT»(ref-349-S28447731102000030800000) under TESTING. If, after performing intake door motor circuit test, symptom still persists, perform a system operational check and check for other symptoms. See «OPERATIONAL CHECK»(ref-349-S23179882482000030800000) . If no other symptom exists, replace auto amplifier.

BLOWER MOTOR MALFUNCTIONING

Start engine. Rotate fan control switch through all 4 blower speeds. Ensure fan speed operates and increases appropriately. Leave fan on maximum position. If system functions as specified, system is okay at this time. If system does not function as specified, perform blower motor circuit test. See BLOWER MOTOR CIRCUIT under TESTING. If, after performing blower motor circuit test, symptom still persists, perform a system operational check and check for other symptoms. See OPERATIONAL CHECK . If no other symptom exists, replace auto amplifier.

BLOWER MOTOR WILL NOT OPERATE IN AUTO POSITION

Start engine. Rotate fan control switch through all 4 blower speeds. Ensure fan speed operates and increases appropriately. Leave fan on maximum position. If system functions as specified, system is okay at this time. If system does not function as specified, perform blower motor auto circuit test. See BLOWER MOTOR AUTO CIRCUIT under TESTING. If blower motor auto circuit is okay, check fan switch. See FAN SWITCH under TESTING. If, after performing fan switch test, symptom still persists, perform a system operational check and check for other symptoms. See OPERATIONAL CHECK . If no other symptom exists, replace auto amplifier.

IMPROPERLY OPERATING TEMPERATURE CONTROL

1. Start engine. Rotate blower control switch to AUTO. Turn A/C on. Ensure A/C switch light illuminates and compressor is engaged. If system functions as specified, system is okay at this time. If system does not function as specified, go to next step.
2. Check compressor belt tension. See «SPECIFICATIONS»(ref-349-S23988023142000030800000) . Adjust or replace as necessary. If belt tension is okay, check for correct refrigerant level. See «SPECIFICATIONS»(ref-349-S23988023142000030800000) . If refrigerant level is okay, go to next step.
3. Check temperature control circuit. See «TEMPERATURE CONTROL CIRCUIT»(ref-349-S35746434152000030800000) under TESTING. Repair or replace as necessary. If temperature control circuit is okay, go to next step.
4. If symptom still persists, perform a system operational check. See «OPERATIONAL CHECK»(ref-349-S23179882482000030800000) . If no other symptom exists, replace auto amplifier.

INSUFFICIENT COOLING

1. Start engine. Rotate blower control switch to high. Turn A/C on. Turn temperature knob to 65°F (18°C). Check for cold air at discharge air outlets. If system functions as specified, system is okay at this time. If system does not function as specified, go to next step.
2. Check compressor belt tension. See «SPECIFICATIONS»(ref-349-S23988023142000030800000) . Adjust or replace as necessary. If belt tension is okay, check air mix door operation. Check air mix door adjustment. See «AIR MIX DOOR»(ref-349-S09585122422000030800000) under ADJUSTMENTS. If adjustment is okay, check air mix door motor operation. See «AIR MIX DOOR MOTOR & POTENTIOMETER BALANCE RESISTOR (PBR)»(ref-349-S34378182882000030800000) under TESTING. If air mix door motor operation is okay, check air mix door motor circuit. See «AIR MIX DOOR MOTOR CIRCUIT»(ref-349-S18747533052000030800000) under TESTING. If air mix door operation is okay, check cooling fan operation. Repair or replace as necessary. If cooling fan is okay, go to next step.
3. Check for correct refrigerant level. See «SPECIFICATIONS»(ref-349-S23988023142000030800000) . If refrigerant level is okay, check for evaporator coil freeze up. If evaporator coil is freezing up, replace A/C compressor. If A/C compressor is okay, check for air leaks in ducting.
4. If symptom still persists, perform a system operational check. See «OPERATIONAL CHECK»(ref-349-S23179882482000030800000) . If no other symptom exists, replace auto amplifier.

INSUFFICIENT HEATING

1. Start engine and bring to normal operating temperature. Turn on blower motor. Select foot mode. Move temperature control knob to 85°F (30°C). If hot air does not flow from floor vents, check for proper coolant level, kinked or leaking hoses, faulty radiator cap or air in cooling system. Repair cooling system as necessary. If cooling system is okay, go to next step.
2. Check heater valve control rod adjustment. See «HEATER VALVE CONTROL ROD»(ref-349-S09507989822000030800000) under ADJUSTMENTS. Adjust or replace as necessary. If heater valve control rod adjustment is okay, go to next step.
3. Check air mix door adjustment. See «AIR MIX DOOR»(ref-349-S09585122422000030800000) under ADJUSTMENTS. Adjust or replace as necessary. If air mix door adjustment is okay, go to next step.
4. Remove instrument panel. Visually inspect air mix door operation. If air mix door does not operate appropriately, replace air mix door. If air mix door operates appropriately, go to next step.
5. Check for leaking air ducts. Repair or replace as necessary. If air ducts are okay, go to next step.
6. Start engine and bring to normal operating temperature. Check inlet and outlet heater hoses by feel. If both heater hoses are warm, go to next step. If both heater hoses are cold, check thermostat installation and operation. Replace if necessary.
7. Ensure heater hoses are properly installed. Backflush heater core and refill system with coolant. If both hoses are still warm, replace heater core. If inlet hose is warmer than the outlet hose, heating system is working properly.
8. If symptom still persists, perform a system operational check. See «OPERATIONAL CHECK»(ref-349-S23179882482000030800000) .

INTAKE DOOR POSITION DOES NOT CHANGE TO FRESH IN DEFROST OR FOOT/DEFROST MODES

1. Start engine. Depress recirculation switch. Ensure recirculation switch illuminates. Listen for intake door position to change (slight change in sound). Ensure recirculation switch turns off when mode position switch is rotated to defrost position or foot/defrost position.
2. Check intake door motor and microswitch operation. See «INTAKE DOOR MOTOR»(ref-349-S38288381102000030800000) and «MICROSWITCH»(ref-349-S08696582462000030800000) under TESTING. If intake door motor and microswitch are not okay, check intake door motor circuit. See «INTAKE DOOR MOTOR CIRCUIT»(ref-349-S28447731102000030800000) under TESTING. If intake door motor and circuit are okay, go to next step.
3. If symptom still persists, perform a system operational check and check for other symptoms. See «OPERATIONAL CHECK»(ref-349-S23179882482000030800000) . If no other symptom exists, replace auto amplifier.

STARTING FAN SPEED CONTROL MALFUNCTIONING

Start engine. Leave fan on AUTO position. Set temperature to 75°F (24°C) and rotate mode control switch through all mode positions. Ensure air is discharged appropriately. See AIR DISTRIBUTION RATIOS table. If system functions as specified, system is okay at this time. If system does not function as specified, perform starting fan speed control circuit test. See STARTING FAN SPEED CONTROL CIRCUIT under TESTING. If, after performing starting fan speed control circuit test, symptom still persists, perform a system operational check and check for other symptoms. See OPERATIONAL CHECK . If no other symptom exists, replace auto amplifier.

A/C COMPRESSOR CLUTCH CIRCUIT

1. Disconnect compressor clutch connector. Start engine and allow it to idle. Turn A/C on. Turn blower motor on. Check for 12 volts at compressor clutch harness connector terminal. If reading is as specified, apply power to A/C compressor clutch. If A/C compressor clutch does not engage, check compressor clutch clearance. Clearance should be.012-.024" (.3-.6 mm). Repair or replace as necessary. If reading is not as specified, go to next step.
2. Turn ignition off. Disconnect A/C relay. Check continuity of Black/White wire between A/C compressor clutch coil harness connector terminal and A/C relay harness connector terminal No. 5. If continuity exists, go to next step. If continuity does not exist, repair Black/White wire as necessary. See «WIRING DIAGRAMS»(ref-349-S15951319732000030800000).
3. Turn ignition on. Measure voltage between ground and A/C relay harness connector terminals No. 2 and 3 (Green/White wires). Both readings should indicate 12 volts. If readings are as specified, go to next step. If readings are not as specified, inspect fuse No. 6 (7.5-amp) in fuse block. Fuse block is located at lower left side of instrument panel. If fuse is blown, repair short in Green/White wire between fuse block and A/C relay connector. If fuse is okay, repair open in Green/White wire between fuse block and A/C relay connector.
4. Test A/C relay. See «A/C RELAY»(ref-349-S15150035552000030800000). Replace relay if faulty. If A/C relay is okay, install A/C relay and go to next step.
5. Ensure ignition is on. Turn A/C switch on. Backprobe between ground and Engine Control Module (ECM) connector terminal No. 12 (Green/Red wire). (Scheme 9) If reading is 12 volts, go to step 7. If reading is not 12 volts, turn ignition off, disconnect A/C relay and ECM connectors and go to next step.
6. Check for continuity in Green/Red wire between ECM harness connector terminal No. 12 and A/C relay harness connector terminal No. 1. If continuity exists, check wire for a short. See «WIRING DIAGRAMS»(ref-349-S15951319732000030800000). If continuity does not exist, check wire for an open. Repair as necessary.
7. Backprobe between ground and ECM connector terminal No. 21 (Black/White wire). If reading is 12 volts, turn ignition off. Disconnect ECM connector and dual-pressure switch connector. If reading is not 12 volts, check ECM operation. See appropriate SELF-DIAGNOSTICS article in ENGINE PERFORMANCE.
8. Check continuity of Black/White wire between ECM harness connector terminal No. 21 and dual-pressure switch harness connector terminal No. 2. If continuity exists, go to next step. If continuity does not exist, repair Black/White wire.
9. Inspect dual-pressure switch. See «DUAL-PRESSURE SWITCH»(ref-349-S40387557272000030800000). Replace as necessary. If okay, go to next step.
10. Disconnect A/C switch. Check continuity of Blue/Black wire between dual-pressure switch harness connector terminal No. 1 and A/C switch harness connector terminal No. 2. If continuity exists, check for short in Blue/Black wire. If wire is okay, go to next step. If continuity does not exist, repair Blue/Black wire.
11. Inspect A/C switch. See «A/C SWITCH»(ref-349-S10597268212000030800000). Replace A/C switch if faulty. If okay, disconnect fan switch harness connector and go to next step.
12. Check continuity of Blue/Red wire between A/C switch harness connector terminal No. 1 and fan switch harness connector terminal No. 1. If continuity exists, go to next step. If continuity does not exist, repair Blue/Red wire.
13. Check for continuity between fan switch harness connector terminal No. 6 (Black wire) and ground. If continuity exists, go to next step. If continuity does not exist, repair Black wire as necessary.
14. Inspect fan switch. See «FAN SWITCH»(ref-349-S40387557272000030800000). Replace fan switch if faulty.

Scheme 9

A/C RELAY

Apply positive battery voltage to A/C relay terminal No. 1 and ground terminal No. 2. (Scheme 10) Check for continuity between terminals No. 3 and 5. If continuity exists, relay is okay. If continuity does not exist, replace relay.

Scheme 10

A/C SYSTEM PERFORMANCE

1. Park vehicle out of direct sunlight. Close all doors. Open engine hood and driver-side window. Connect A/C manifold gauge set. Determine relative humidity and ambient air temperature. Insert thermometer at center vent outlet.
2. Set temperature control lever to maximum cold setting, air control lever to vent position, and fresh/recirculated air lever to recirculated air position. Turn blower fan switch to highest position. Operate engine at idle.
3. After running A/C for at least 10 minutes, check temperature at center vent outlet and high-side and low-side system pressures. Ensure system is operating within specified range. See «A/C SYSTEM PERFORMANCE (RECIRCULATING-TO-DISCHARGE AIR TEMP.)»(ref-349-S21008235192000030800000) and «A/C SYSTEM PRESSURES»(ref-349-S37317845662000030800000) tables.

A/C SYSTEM PERFORMANCE (RECIRCULATING-TO-DISCHARGE AIR TEMP.)

A/C SYSTEM PRESSURES

Disconnect negative battery cable. Remove A/C switch from control panel. Check continuity between Blue/Red wire terminal and Blue/Black wire terminal of A/C switch. With A/C switch on (button pressed in), there should be continuity. With A/C switch off (button popped out), there should be no continuity. If continuity is not as specified, replace A/C switch.

Air Mix Door Motor

Door motor is attached to heater unit. (Scheme 4) Disconnect motor connector. Connect positive battery lead to Yellow/Red wire terminal and negative battery lead to Brown/White wire terminal of motor. Ensure air mix door moves from cold position to hot position (clockwise). Reverse battery leads and ensure door moves in opposite direction (counterclockwise).

1. PBR is built into air mix door motor. PBR informs auto amplifier of air mix door position. Disconnect air mix door motor connector. Connect ohmmeter leads to Green/White wire and Yellow/Black wire terminals of air mix door motor. Operate air mix door motor, and check resistance of PBR. See «PBR RESISTANCE»(ref-349-S19561902982000030800000) table.
2. Reconnect air mix door motor connector. Turn ignition on. Using voltmeter, backprobe Green/White wire and Yellow/Black wire terminals of motor connector. Move temperature control lever from 65°F (18°C) setting to 85°F (32°C) setting. Ensure voltmeter needle moves smoothly from zero volts to 5 volts. Move temperature control lever from 85°F (32°C) setting to 65°F (18°C) setting. Ensure voltmeter needle moves smoothly from 5 volts to zero volts.

PBR RESISTANCE

AIR MIX DOOR MOTOR CIRCUIT

1. Check auto amplifier power supply circuit. See «AUTO AMPLIFIER POWER SUPPLY & GROUND CIRCUIT CHECK»(ref-349-S42717489692000030800000) . Repair or replace as necessary. If power supply circuit is okay, go to next step.
2. Check ambient temperature sensor circuit. See «AMBIENT TEMPERATURE SENSOR CIRCUIT»(ref-349-S18273547282000030800000) . Repair or replace as necessary. If ambient temperature sensor circuit is okay, go to next step.
3. Check in-vehicle temperature sensor circuit. See «IN-VEHICLE TEMPERATURE SENSOR CIRCUIT»(ref-349-S40469267152000030800000) . Repair or replace as necessary. If in-vehicle temperature sensor circuit is okay, go to next step.
4. Check Potentiometer Temperature Control (PTC). See «POTENTIOMETER TEMPERATURE CONTROL (PTC)»(ref-349-S32227478592000030800000) . Replace as necessary. If PTC is okay, go to next step.
5. Check Potentiometer Balance Resistor (PBR). See «AIR MIX DOOR MOTOR & POTENTIOMETER BALANCE RESISTOR (PBR)»(ref-349-S37730423802000030800000) . Replace as necessary. If PBR is okay, go to next step.
6. Turn ignition on. Backprobing, measure voltage between ground and air mix door motor connector terminals. Move air mix door from cold to hot position (clockwise), and then from hot to cold (counterclockwise). Voltage reading of 10.5 volts should exist at air mix door motor connector terminal No. 5 (Brown/White wire), and then No. 4 (Yellow/Red wire). If voltage exists, go to next step. If voltage does not exist, replace auto amplifier.
7. Disconnect air mix door motor and auto amplifier connectors. Check for continuity between air mix door motor harness connector terminals No. 5 (Brown/White wire) and No. 4 (Yellow/Red wire), and auto amplifier harness connector terminals No. 6 (Brown/White wire) and No. 5 (Yellow/Red wire). If continuity exists, check for a short to ground. Repair or replace as necessary. See «WIRING DIAGRAMS»(ref-349-S15951319732000030800000) . If continuity does not exist, replace air mix door motor.

AMBIENT & IN-VEHICLE TEMPERATURE SENSORS

Ambient sensor is mounted on radiator support center brace. In-vehicle temperature sensor is attached to instrument panel lower cover. Turn ignition off. Disconnect temperature sensor connector. (Scheme 3)or (Scheme 4). Using an ohmmeter, measure resistance between sensor terminals. See AMBIENT & IN-VEHICLE TEMPERATURE SENSOR RESISTANCE table. If resistance is not as specified, replace sensor.

AMBIENT & IN-VEHICLE TEMPERATURE SENSOR RESISTANCE

AMBIENT TEMPERATURE SENSOR CIRCUIT

1. Disconnect ambient temperature sensor connector. Turn ignition on. Measure voltage between ground and ambient temperature sensor connector terminal No. 1 (Blue/Red wire). If 5 volts exist, go to next step. If 5 volts do not exist, go to step 4 .
2. Disconnect auto amplifier connector. Check for continuity in Green/White wire between ambient temperature sensor harness connector terminal No. 2 and auto amplifier harness connector terminal No. 20. If continuity exists, check for a short in wire harness. Repair or replace as necessary. See «WIRING DIAGRAMS»(ref-349-S15951319732000030800000) . If wire is okay, go to next step.
3. Check ambient temperature sensor. See «AMBIENT & IN-VEHICLE TEMPERATURE SENSORS»(ref-349-S16119856752000030800000) . Replace as necessary. If ambient temperature sensor is okay, replace auto amplifier.
4. Disconnect auto amplifier connector. Check for continuity in Blue/Red wire between ambient temperature sensor harness connector terminal No. 1 and auto amplifier harness connector terminal No. 15. If continuity does not exist, check for a short in wire harness. Repair or replace as necessary. See «WIRING DIAGRAMS»(ref-349-S15951319732000030800000) . If wire is okay, replace auto amplifier.

Hold a smoking object (i.e., lit cigarette) in front of in-vehicle temperature sensor vent. Ensure smoke is drawn into in-vehicle temperature sensor vent.

AUTO AMPLIFIER POWER SUPPLY & GROUND CIRCUIT CHECK

1. Disconnect auto amplifier connector. Turn ignition on. Measure voltage at terminal No. 1 (Green/Red wire) of harness connector. (Scheme 11) If 12 volts exist, go to next step. If 12 volts do not exist, repair open or short in Green/Red wire. See «WIRING DIAGRAMS»(ref-349-S15951319732000030800000).
2. Turn ignition off. Check continuity between terminal No. 3 (Black wire) of harness connector and chassis ground. Ensure continuity exists. If continuity does not exist, repair open in Black wire.

BLOWER MOTOR AUTO CIRCUIT

1. Rotate fan control switch to AUTO. Backprobing, measure voltage between fan control amplifier connector terminal No. 2 and ground. If 2.5-9.0 volts exist, go to next step. If 2.5-9.0 volts do not exist, replace fan control amplifier.
2. Disconnect fan switch and auto amplifier connectors. Check for continuity in Light Green/Red wire between fan switch harness connector terminal No. 5 and auto amplifier harness connector terminal No. 25. If continuity exists, check wire harness for a short. Repair or replace as necessary. See «WIRING DIAGRAMS»(ref-349-S15951319732000030800000) . If wire is okay, go to next step.
3. Check for continuity in Black wire between fan switch harness connector terminal No. 6 and ground. If continuity exists, check wire harness for a short. Repair or replace as necessary. If wire is okay, go to next step.
4. Check fan switch. See «FAN SWITCH»(ref-349-S38200447332000030800000) . Replace as necessary. If fan switch is okay, replace auto amplifier.

Scheme 11

1. Disconnect fan control amplifier. (Scheme 4) Turn ignition to ACC position. Using a DVOM, check for voltage between ground and fan control amplifier harness connector terminal No. 1 (Blue/White wire). If 12 volts exist, go to next step. If 12 volts do not exist, go to step 7.
2. Turn ignition off. Check for continuity between ground and fan control amplifier harness connector terminal No. 3 (Black wire). If continuity does not exist, repair or replace Black wire as necessary. If continuity exists, connect fan control amplifier connector and go to next step.
3. Turn ignition on. Measure voltage (backprobe) between ground and fan control amplifier harness connector terminal No. 2 (Blue/Yellow wire), while selecting specified fan speeds. With fan control knob at speed I (low) position, reading should be 2.5-3.0 volts. (Scheme 2) With fan control knob at speed III (high) position, reading should be 8.5-9.0 volts. If readings are as specified, replace fan control amplifier. If readings are not as specified, go to next step.
4. Turn ignition off. Disconnect auto amplifier and fan control amplifier connectors. Check for continuity of Blue/Yellow wire between auto amplifier harness connector terminal No. 21 and fan control amplifier harness connector terminal No. 2. (Scheme 11) If continuity exists, check wire for a short. See «WIRING DIAGRAMS»(ref-349-S15951319732000030800000). If wire is okay, go to next step. If continuity does not exist, repair Blue/Yellow wire circuit.
5. Turn ignition to ACC position. Measure voltage between ground and auto amplifier harness connector terminal No. 24 (Blue wire). (Scheme 11) If about 12 volts exist, go to next step. If about 12 volts do not exist, check 15-amp fuses No. 1 and 2 in fuse block. Fuse block is located at lower left side of instrument panel. If fuses are blown, check for short in Blue wire between auto amplifier harness connector terminal No. 24 and fuses No. 1 and 2 in fuse block. If fuses are okay, check for open in Blue wire.
6. Check for voltage between ground and auto amplifier harness connector terminal No. 22 (Blue/White wire). (Scheme 11) If reading indicates about 12 volts, replace auto amplifier. If reading does not indicate about 12 volts, go to step 10.
7. Disconnect blower motor connector. Ensure ignition is in ACC position. Measure voltage between ground and blower motor harness connector terminal No. 1 (Blue wire). If reading indicates about 12 volts, go to next step. If reading is not as specified, check 15-amp fuses No. 1 and 2 in fuse block. Fuse block is located at lower left side of instrument panel.
8. Turn ignition off. Check continuity of Blue/White wire between blower motor harness connector terminal No. 2 and fan control amplifier harness connector terminal No. 1. If continuity exists, check Blue/White wire for a short. If wire is okay, go to next step. If continuity does not exist, repair Blue/White wire circuit as necessary. See «WIRING DIAGRAMS»(ref-349-S15951319732000030800000).
9. Check blower motor. Replace as necessary. If okay, go to next step.
10. Ensure ignition is off. Check continuity of Blue/White wire between blower motor harness connector terminal No. 2 and auto amplifier harness connector terminal No. 22. (Scheme 11) If continuity does not exist, repair Blue/White wire circuit as necessary. If continuity exists, check Blue/White wire for a short.

DUAL-PRESSURE SWITCH

Remove dual-pressure switch connector. Using ohmmeter, check continuity between dual-pressure switch terminals under specific test conditions. See DUAL-PRESSURE SWITCH TEST table. Replace switch if it does not perform as indicated.

DUAL-PRESSURE SWITCH TEST

FAN SWITCH

Disconnect fan switch connector. (Scheme 12) Check continuity between indicated terminals with fan switch in specified position. See FAN SWITCH CONTINUITY TEST table. Replace switch if continuity is not as specified.

FAN SWITCH CONTINUITY TEST

Scheme 12

INTAKE DOOR MOTOR

Motor is installed on the intake unit. Disconnect intake door motor connector. Connect positive battery lead to Green/Red wire terminal and negative battery lead to Green/Black wire terminal of motor. Ensure intake door moves to recirculated air position. Reverse battery leads to motor. Ensure intake door moves to fresh air position.

INTAKE DOOR MOTOR CIRCUIT

1. Disconnect intake door motor connector. Turn ignition on. Using a DVOM, check for voltage between intake door motor harness connector terminal No. 1 (Green/Red) and ground. If about 12 volts exist, go to next step. If about 12 volts do not exist, check fuse No. 6 (7.5-amp). Fuse No. 6 is located in fuse block at lower left side of instrument panel. If fuse is blown, check for short in Green/Red wire. If fuse is okay, check for open in Green/Red wire.
2. Turn ignition off. Place recirculation switch in recirculation mode. Continuity should exist between ground and intake door motor harness connector terminal No. 2 (Green/Black wire), and should not exist between ground and terminal No. 3 (Blue/White). Place recirculation switch in fresh mode. Continuity should not exist between ground and intake door motor harness connector terminal No. 2 (Green/Black wire), and should exist between ground and terminal No. 3 (Blue/White wire). If readings are as specified, go to next step. If readings are not as specified, go to step 4 .
3. Check intake door linkage. See «INTAKE DOOR»(ref-349-S09507989822000030800000) under ADJUSTMENTS. If okay, replace intake door motor. If not okay, adjust linkage as necessary.
4. Disconnect mode switch connector. Check continuity of Blue/White wire and Green/Black wire between mode switch harness connector terminals No. 2 and 1 and intake door switch harness connector terminals No. 3 and 2. If continuity exists, check wires for a short. See «WIRING DIAGRAMS»(ref-349-S15951319732000030800000) . If wire is okay, go to next step. If continuity does not exist, repair open wire or harness connector of related circuit.
5. Check mode switch. See «MODE SWITCH»(ref-349-S17489934992000030800000) . Replace as necessary. If mode switch is okay, go to next step.
6. Disconnect recirculation switch connector. Check continuity of Black wire between mode switch harness connector terminal No. 4 and recirculation switch harness connector terminal No. 4. If continuity exists, check wire for a short. If wire is okay, go to next step. If continuity does not exist, replace mode switch.
7. Check continuity between mode switch harness connector terminal No. 4 (Black wire) and ground. If continuity exists, check wire for a short. See «WIRING DIAGRAMS»(ref-349-S15951319732000030800000) . If wire is okay, go to next step. If continuity does not exist, repair wiring harness as necessary.
8. Check recirculation switch. See «RECIRCULATION SWITCH»(ref-349-S21699973692000030800000) . Replace switch as necessary.

IN-VEHICLE TEMPERATURE SENSOR CIRCUIT

1. Disconnect in-vehicle temperature sensor connector. Turn ignition on. Measure voltage between ground and in-vehicle temperature sensor connector terminal No. 2 (Pink/Blue wire). If 5 volts exist, go to next step. If 5 volts do not exist, go to step 4 .
2. Disconnect auto amplifier connector. Check for continuity in Green/White wire between in-vehicle temperature sensor harness connector terminal No. 1 and auto amplifier harness connector terminal No. 20. If continuity exists, check for a short in wire harness. Repair or replace as necessary. If wire is okay, go to next step.
3. Check in-vehicle temperature sensor. See «AMBIENT & IN-VEHICLE TEMPERATURE SENSORS»(ref-349-S16119856752000030800000) . Replace as necessary. If in-vehicle temperature sensor is okay, replace auto amplifier.
4. Disconnect auto amplifier connector. Check for continuity in Pink/Blue wire between in-vehicle temperature sensor harness connector terminal No. 2 and auto amplifier harness connector terminal No. 14. If continuity exists, check for a short in wire harness. See «WIRING DIAGRAMS»(ref-349-S15951319732000030800000) . Repair or replace as necessary. If wire is okay, replace auto amplifier.

MICROSWITCH

Microswitch is installed around side link of heater unit. Microswitch operates link in response to mode switch position. Disconnect microswitch connector. (Scheme 4) Check continuity between indicated terminals with mode switch at specified position. Replace microswitch if continuity is not as specified. See MICROSWITCH CONTINUITY TEST table.

MICROSWITCH CONTINUITY TEST

MODE SWITCH

Disconnect recirculation switch and mode switch connectors. (Scheme 13) Check continuity between indicated terminals with mode switch in specified position. See MODE SWITCH CONTINUITY TEST table. Replace switch if continuity is not as specified.

MODE SWITCH CONTINUITY TEST

Disconnect PTC harness connector. Connect ohmmeter leads to PTC terminals No. 1 (Green/White wire) and No. 2 (Red/Green wire). Move temperature control knob from full cold setting to full hot setting. Ensure resistance increases smoothly from zero ohms to 1000 ohms.

Disconnect negative battery cable. Remove recirculation switch from control panel. With recirculation switch on (button pressed in), there should be continuity between terminals No. 1 and 4. With recirculation switch off (button popped out), there should be continuity between terminals No. 2 and 4. If continuity is not as specified, replace recirculation switch. (Scheme 13)

Scheme 13

Scheme 14

1. Disconnect thermal transmitter and microswitch connectors. (Scheme 14) Check for continuity in Yellow/Red wire between thermal transmitter harness connector terminal and microswitch harness connector terminal No. 1. If continuity exists, check wire harness for a short. See «WIRING DIAGRAMS»(ref-349-S15951319732000030800000). Repair or replace as necessary. If wire is okay, go to next step.
2. Check microswitch operation. See «MICROSWITCH»(ref-349-S08696582462000030800000). Replace as necessary. If okay, go to next step.
3. Check thermal transmitter operation. See «THERMAL TRANSMITTER»(ref-349-S33790582702000030800000). Replace as necessary. If okay, go to next step.
4. Disconnect auto amplifier connector. Check for continuity in Red/Yellow wire between auto amplifier harness connector terminal No. 17 and microswitch harness connector terminal No. 3. If continuity exists, check wire harness for a short. Repair or replace as necessary. If wire is okay, replace auto amplifier.

Sensor is located on center defrost grille. Position sunload sensor to get full direct sunlight. Turn ignition on. Backprobe auto amplifier harness connector terminals No. 16 (Light Green/Red wire) and ground. Auto amplifier is located behind instrument panel. (Scheme 4) Ensure voltage is as specified. (Scheme 15)

Scheme 15

SUNLOAD SENSOR CIRCUIT

1. Disconnect sunload sensor connector. Turn ignition on. Measure voltage between ground and sunload sensor connector terminal No. 1 (Light Green/Red wire). If 5 volts exist, go to next step. If 5 volts do not exist, go to step 4 .
2. Disconnect auto amplifier connector. Check for continuity in Green/White wire between sunload sensor harness connector terminal No. 2 and auto amplifier harness connector terminal No. 20. If continuity exists, check for a short in wire harness. Repair or replace as necessary. If wire is okay, go to next step.
3. Check sunload sensor. See «SUNLOAD SENSOR»(ref-349-S31853323992000030800000) . Replace as necessary. If sunload sensor is okay, replace auto amplifier.
4. Disconnect auto amplifier connector. Check for continuity in Light Green/Red wire between sunload sensor harness connector terminal No. 1 and auto amplifier harness connector terminal No. 16. If continuity exists, check for a short in wire harness. Repair or replace as necessary. If wire is okay, replace auto amplifier.

TEMPERATURE CONTROL CIRCUIT

1. Check Potentiometer Balance Resistor (PBR). See «AIR MIX DOOR MOTOR & POTENTIOMETER BALANCE RESISTOR (PBR)»(ref-349-S37730423802000030800000) . If PBR is okay, go to next step. If PBR is not okay, go to step 7 .
2. Inspect ducting. Repair or replace as necessary. If ducting is okay, go to next step.
3. Check in-vehicle temperature sensor circuit. See «IN-VEHICLE TEMPERATURE SENSOR CIRCUIT»(ref-349-S40469267152000030800000) . Repair or replace as necessary. If in-vehicle temperature sensor circuit is okay, go to next step.
4. Check ambient sensor circuit. See «AMBIENT TEMPERATURE SENSOR CIRCUIT»(ref-349-S18273547282000030800000) . Repair or replace as necessary. If ambient sensor circuit is okay, go to next step.
5. Check sunload sensor circuit. See «SUNLOAD SENSOR CIRCUIT»(ref-349-S05368943962000030800000) . If sunload sensor circuit is not okay, replace sunload sensor or auto amplifier. If sunload sensor circuit is okay, go to next step.
6. Check auto amplifier power supply and ground circuits. See «AUTO AMPLIFIER POWER SUPPLY & GROUND CIRCUIT CHECK»(ref-349-S42717489692000030800000) . If auto amplifier power supply and ground circuits are okay, replace auto amplifier. If auto amplifier power supply and ground circuits are not okay, repair appropriate harness or connector. See «WIRING DIAGRAMS»(ref-349-S15951319732000030800000) .
7. Check Potentiometer Temperature Control (PTC). See «POTENTIOMETER TEMPERATURE CONTROL (PTC)»(ref-349-S32227478592000030800000) . Replace PTC as necessary. If PTC is okay, go to next step.
8. Check air mix door adjustment. See «AIR MIX DOOR»(ref-349-S09585122422000030800000) under ADJUSTMENTS. Repair or adjust as necessary. If air mix door adjustment is okay, replace Potentiometer Balance Resistor (PBR).

THERMAL TRANSMITTER

Turn ignition off. Disconnect thermal transmitter connector. (Scheme 14) Using an ohmmeter, measure resistance between thermal transmitter terminal and ground. Resistance should be approximately 170-210 ohms at 140°F (60°C) or 47-53 ohms at 212°F (100°C). If resistance is not as specified, replace thermal transmitter.