A/c-Heater System - Automatic Subaru Legacy BC/BJ/BF

A/C SYSTEM SPECIFICATIONS

A/C SYSTEM SPECIFICATIONS

DESCRIPTION

Automatic Climate Control (ACC) system uses a microprocessor located in the auto amplifier (control unit) to control passenger compartment temperature. A/C system components include compressor, condenser, evaporator, receiver-drier, water temperature sensor, ambient temperature sensor, pressure switch, intake sensor, sunload sensor, in-vehicle sensor, condenser fan and related vents, wiring and fuses. (Scheme 1)

Scheme 1

SYSTEM OPERATION

Passenger compartment temperature is set at A/C control panel on auto amplifier. Auto amplifier uses sensor inputs to determine how to adjust air to selected temperature. Auto amplifier uses actuators to control airflow doors.

AUTO AMPLIFIER

Auto amplifier is used to set desired temperature and controls the compressor, blower motor and actuators to adjust passenger compartment temperature. Actuators position airflow doors according to temperature requirements. Other push button switches control fan speed and rear window defogger.

SENSORS

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

THERMO AMPLIFIER

Thermo amplifier, located in evaporator housing, senses low evaporator temperature. During periods of low outside ambient temperatures, evaporator core freezing is prevented by cycling compressor clutch.

INTAKE AIR DOOR MOTOR

Intake air door motor opens and closes recirculating and fresh air doors. Motor is mounted behind dash on passenger side of vehicle. The recirculation (CIRC) button on control panel can manually override fresh air function. Override will cancel in approximately 10 minutes. If selected temperature is 65°F (18°C), intake air door will remain in recirculate position.

AIR MIX DOOR MOTOR

Air mix door, located below heater box, provides dehumidification and temperature control. Air mix door motor controls position of air mix door, which controls mix of air through evaporator core and heater core. Potentio-Balance Resistor (PBR) indicates air mix door position to auto amplifier.

FAN CONTROL AMPLIFIER

Fan control amplifier is a transistorized device which controls fan speed. Fan speed is controlled by varying voltage through ground connection. Fan speed is controlled by auto amplifier in 13 steps from 5-10.5 volts. When voltage is more than 10.5 volts, high relay is activated, providing maximum blower speed. If temperature is set at 65°F (18°C) or 85°F (29°C), blower speed will be set at maximum.

OUTLET (MODE) DOOR MOTOR

Mode door motor is a bidirectional motor, which controls distribution of air to vent, defrost and heater registers. A position switch indicates door position to auto amplifier. Motor directional control is through polarity reversal.

ENGLISH/METRIC SELECTION

To display temperature in degrees Celsius (°C) disconnect English/Metric connector "A" from English/Metric connector "B" under dash on passenger side of vehicle. (Scheme 2) To display temperature in degrees Fahrenheit (°F), reconnect English/Metric connectors "A" and "B".

Scheme 2

Power Supply

Measure battery voltage and specific gravity of electrolyte. If battery voltage is not 12 volts or if specific gravity is less than 1.260, replace battery. Check fuses for A/C system and heater. Check condition of harness and connectors. Repair as necessary.

Refrigerant Line

Check amount of refrigerant in system through sight glass. Install manifold gauge and check refrigerant line pressure. See SPECIFICATIONS TABLE at beginning of article. Evacuate refrigeration, system and recharge as necessary.

Control Linkage

Check functioning of control rod and linkages for mode door, air mix door and intake door. Repair or adjust as necessary.

BASIC CHECKS

Note. For BASIC CHECKS, turn ignition switch to ON position. If any BASIC CHECKS fail to function as described, proceed to SELF-DIAGNOSTIC SYSTEM.

Low/High Blower Fan Switch Operational Checks

1. Press LO switch. (Scheme 3) Blower should operate on low speed and indicator light should come on.
2. Press LO switch again. Blower should stop and indicator light should go out. Press LO switch again. Blower should operate at low speed.
3. Press HI switch. Low speed indicator light should go out and high speed indicator light should come on. Blower should operate at high speed. Press HI switch again. Blower should stop and indicator light should go out.

Scheme 3

Recirculation (CIRC) Switch Operational Check

1. Press LO switch to start blower. (Scheme 3) Press CIRC switch. CIRC switch indicator light should come on and intake door should change position (blower sound should change slightly).
2. Press CIRC switch again. Indicator light should go out and intake door should change position again.

Defroster (DEF) Switch Operational Check

1. Press LO switch to start blower. (Scheme 3) Press CIRC switch. Press DEF switch.
2. CIRC switch indicator light should go out and DEF switch indicator light should come on. Airflow should be directed to defrost vents.
3. Ensure compressor clutch is engaged. Press DEF switch again. Defroster should still operate.

ECONO Mode Operational Check

1. Press ECONO switch. (Scheme 3) Defrost function should be canceled and DEF switch indicator light should go out. ECONO indicator light should come on.
2. Discharged air outlet will depend on ambient, passenger compartment and set temperatures. Ensure compressor clutch is not engaged.

AUTO Mode Operational Check

Press AUTO switch. (Scheme 3) Ensure compressor clutch engages and AUTO switch indicator light glows. Discharged air outlet will depend on ambient, cabin and set temperatures.

Temperature Decrease Function Operational Check

Press COLD switch (down arrow) until 68°F (20°C) is displayed. (Scheme 3) Ensure cold air comes out of outlets.

Temperature Increase Function Operational Check

Press HOT switch (up arrow) until 80°F (30°C) is displayed. (Scheme 3) Listen for changes in blower speed and ensure hot air comes out of outlets.

Memory Function Operational Check

Press OFF switch. (Scheme 3) Turn ignition off and wait for 15 seconds. Turn ignition on. Press AUTO switch. Ensure set temperature is 90°F (32°C).

Ambient Display Check

Press OUT TEMP switch. (Scheme 3) Outside temperature should flash for 5 seconds.

SELF-DIAGNOSTIC SYSTEM

Self-diagnostic system detects problems in sensors, motors and other components by monitoring each circuit.

Entering Self-Diagnostics

1. Start engine. Using a jumper wire, ground self-diagnostic test lead. (Scheme 4) Auto amplifier will enter DIAGNOSTIC STEP 1 of self-diagnostic procedure.
2. To proceed to next DIAGNOSTIC STEP, press HOT switch. (Scheme 3) To return to previous DIAGNOSTIC STEP, press COLD switch.

Exiting Self-Diagnostics

To exit from self-diagnostics, turn ignition off and disconnect self-diagnostic test lead connector ground. (Scheme 4)

Scheme 4

Indicator & Switch Inspection

1. Indicator lights should flash and temperature display should indicate -188 (all segments lit). (Scheme 3)
2. If indicators DO NOT flash, or temperature display does not indicate -188, replace auto amplifier. See «AUTO AMPLIFIER»(/subaru/legacy/bcbjbf-1989-1994/remont/automatic-hvac-system/#ac-heater-system-automatic) under REMOVAL & INSTALLATION. If indicator lights and temperature display segments are okay, go to next step.
3. Press HOT switch. Temperature display should indicate 2. Press COLD switch. Indicator lights should flash again and temperature display should indicate -188. This indicates proper operation of HOT and COLD switches.
4. If switches are okay, go to DIAGNOSTIC STEP 2. If switches are not okay, replace auto amplifier. See «AUTO AMPLIFIER»(/subaru/legacy/bcbjbf-1989-1994/remont/automatic-hvac-system/#ac-heater-system-automatic) under REMOVAL & INSTALLATION.

Sensor Circuit Inspection

1. Press HOT switch. (Scheme 3) Temperature display should indicate 2. After approximately 4 seconds, display should indicate a code. See «SENSOR CIRCUIT TROUBLE CODES TABLE»(/subaru/legacy/bcbjbf-1989-1994/remont/automatic-hvac-system/#ac-heater-system-automatic).
2. Multiple malfunctions blink twice in succession. Proceed to appropriate code testing procedure under TESTING.
3. If all sensors are okay (Code 20 displayed), go to DIAGNOSTIC STEP 3.

SENSOR CIRCUIT TROUBLE CODES

Actuator Inspection

1. Press HOT switch. (Scheme 3) Temperature display should read 31. Check compressor and blower operation and positioning of mode door motor, intake door motor and air mix door motor. See «ACTUATOR OPERATION SPECIFICATIONS»(/subaru/legacy/bcbjbf-1989-1994/remont/automatic-hvac-system/#ac-heater-system-automatic) table.
2. To advance to next code, press DEF switch. Ensure all actuators operate as specified. If any actuators DO NOT function as specified, test appropriate actuator and circuit. See «TESTING»(/subaru/legacy/bcbjbf-1989-1994/remont/automatic-hvac-system/#ac-heater-system-automatic). If all actuators are okay, go to DIAGNOSTIC STEP 4.

ACTUATOR OPERATION SPECIFICATIONS

Temperature Sensors Inspection

1. Press HOT switch. Temperature display should show 41. Press DEF switch. Temperature display should indicate temperature reading of ambient sensor.
2. Press DEF switch. Temperature display should indicate 42 and then show temperature reading of in-vehicle sensor.
3. Press DEF switch. Temperature display should indicate 43, then show temperature reading of intake sensor. If temperature readings are greatly different from actual temperature, check sensor and circuit. See «TESTING»(/subaru/legacy/bcbjbf-1989-1994/remont/automatic-hvac-system/#ac-heater-system-automatic) .

In-Vehicle Sensor Resistance

1. Turn ignition off. Remove auto amplifier. See «AUTO AMPLIFIER»(/subaru/legacy/bcbjbf-1989-1994/remont/automatic-hvac-system/#ac-heater-system-automatic) under REMOVAL & INSTALLATION.
2. Disconnect in-vehicle sensor harness connector. (Scheme 1) Check resistance between sensor connector terminals. See IN-VEHICLE TEMP SENSOR RESISTANCE SPECIFICATIONS table.
3. If resistance reading is not as specified, replace sensor. If resistance reading is okay, check in-vehicle temperature sensor harness.

IN-VEHICLE TEMP SENSOR RESISTANCE SPECIFICATIONS

In-Vehicle Temperature Sensor Harness Check

1. Connect auto amplifier harness connectors. Turn ignition switch to ON position. Check voltage between in-vehicle temperature sensor harness connector Red wire terminal (No. 1) and chassis ground.
2. If voltage reading is approximately 5 volts, repair open in circuit between White wire terminal of in-vehicle temperature sensor and auto amplifier 16-pin harness connector terminal No. 5. (Scheme 5) If voltage reading is less than 5 volts, check auto amplifier output voltage.

Auto Amplifier Output Voltage Check

1. Unplug auto amplifier 16-pin harness connector. Check voltage between auto amplifier 16-pin connector terminal No. 15 and chassis ground. (Scheme 5)
2. If voltage reading is not approximately 5 volts, go to next step. If voltage is as specified, repair Red wire between in-vehicle temperature sensor harness connector and auto amplifier.
3. Reconnect in-vehicle temperature sensor, and check temperature reading of sensor. See «SELF-DIAGNOSTIC SYSTEM»(/subaru/legacy/bcbjbf-1989-1994/remont/automatic-hvac-system/#ac-heater-system-automatic__self-diagnostic-system) under TROUBLE SHOOTING, and proceed to «DIAGNOSTIC STEP 4»(/subaru/legacy/bcbjbf-1989-1994/remont/automatic-hvac-system/#ac-heater-system-automatic).
4. If in-vehicle sensor temperature reading is incorrect in self-diagnostic procedure, replace auto amplifier. If temperature reading is correct, check and repair harness as necessary.

Scheme 5

Ambient Temperature Sensor Resistance

1. Turn ignition off. Disconnect ambient temperature sensor harness connector.
2. Check resistance between sensor connector terminals. See «AMBIENT TEMP SENSOR RESISTANCE SPECIFICATIONS TABLE»(/subaru/legacy/bcbjbf-1989-1994/remont/automatic-hvac-system/#ac-heater-system-automatic) .
3. If resistance reading is not as specified, replace sensor. If resistance reading is okay, check ambient temperature sensor harness.

AMBIENT TEMP SENSOR RESISTANCE SPECIFICATIONS

Ambient Temperature Sensor Harness Check

1. Turn ignition switch to ON position. Check voltage between ambient temperature sensor harness connector Orange wire terminal (No. 2) and chassis ground.
2. If voltage reading is approximately 5 volts, repair circuit between Yellow/Black wire terminal of ambient temperature sensor and auto amplifier 16-pin harness connector terminal No. 5. (Scheme 5) If voltage reading is not as specified, check auto amplifier output voltage.

1. Remove auto amplifier. See «AUTO AMPLIFIER»(/subaru/legacy/bcbjbf-1989-1994/remont/automatic-hvac-system/#ac-heater-system-automatic) under REMOVAL & INSTALLATION. Unplug 16-pin harness connector of auto amplifier.
2. Turn ignition switch to ON position. Check voltage between auto amplifier 16-pin connector terminal No. 8 and ground. (Scheme 5)
3. If voltage reading is approximately 5 volts, repair Orange wire between ambient temperature sensor and auto amplifier. If voltage reading is not as specified, go to next step.
4. Reconnect auto amplifier and sensor harness connectors. Check temperature reading of ambient temperature sensor. Reconnect ambient temperature sensor. See «SELF-DIAGNOSTIC SYSTEM»(/subaru/legacy/bcbjbf-1989-1994/remont/automatic-hvac-system/#ac-heater-system-automatic__self-diagnostic-system) under TROUBLE SHOOTING, and proceed to «DIAGNOSTIC STEP 4»(/subaru/legacy/bcbjbf-1989-1994/remont/automatic-hvac-system/#ac-heater-system-automatic).
5. If temperature reading of ambient sensor is correct in self-diagnostic procedure, check and repair harness between ambient sensor and auto amplifier. If temperature reading of ambient temperature sensor is incorrect in self-diagnostic procedure, replace auto amplifier.

Intake Temperature Sensor Resistance

1. Turn ignition off. Remove glove box. Disconnect intake temperature sensor harness connector.
2. Check resistance between Yellow wire and Blue/Red wire terminals in sensor connector. See INTAKE TEMP SENSOR RESISTANCE SPECIFICATIONS TABLE.
3. If resistance reading is not as specified, replace sensor. If resistance is okay, check intake temperature sensor harness.

INTAKE TEMP SENSOR RESISTANCE SPECIFICATIONS

Intake Temperature Sensor Harness Check

1. Turn ignition switch to ON position. Check voltage between intake temperature sensor harness connector Yellow wire terminal and chassis ground.
2. If voltage reading is approximately 5 volts, repair circuit between Blue/Red wire terminal of intake sensor and auto amplifier 16-pin harness connector terminal No. 5. (Scheme 5)
3. If voltage reading is not as specified, check auto amplifier output voltage.

1. Remove auto amplifier. See AUTO AMPLIFIER under REMOVAL & INSTALLATION. Unplug only 16-pin harness connector of auto amplifier.
2. Turn ignition switch to ON position. Check voltage between auto amplifier 16-pin connector terminal No. 7 and ground. (Scheme 5)
3. If voltage reading is approximately 5 volts, repair Yellow wire between intake sensor and auto amplifier. If voltage is not as specified, go to next step.
4. Check temperature reading of intake temperature sensor. Reconnect intake temperature sensor and go to SELF-DIAGNOSTIC SYSTEM (DIAGNOSTIC STEP 4) under TROUBLE SHOOTING.
5. If temperature reading of intake temperature sensor is incorrect in self-diagnostic procedure, replace auto amplifier. If temperature reading of intake temperature sensor is okay, check and repair harness between intake sensor and auto amplifier.

Water Temperature Sensor Resistance

1. Turn ignition off. Disconnect water temperature sensor harness connector. Check resistance between sensor connector terminals. See WATER TEMP SENSOR RESISTANCE SPECIFICATIONS TABLE.
2. If resistance reading is not as specified, replace sensor. If resistance reading is okay, check water temperature sensor harness.

WATER TEMP SENSOR RESISTANCE SPECIFICATIONS

Water Temperature Sensor Harness Check

1. Turn ignition switch to ON position. Check voltage between water temperature sensor harness connector Blue/Yellow wire terminal and chassis ground.
2. If voltage reading is approximately 5 volts, repair circuit between Brown wire terminal of water temperature sensor and auto amplifier 16-pin harness connector terminal No. 5. (Scheme 5) If voltage reading is not as specified, check auto amplifier output voltage.

1. Remove auto amplifier. See AUTO AMPLIFIER under REMOVAL & INSTALLATION. Disconnect only auto amplifier 16-pin harness connector. Turn ignition switch to ON position. Check voltage between auto amplifier 16-pin connector terminal No. 6 and chassis ground. (Scheme 5)
2. If voltage reading is not approximately 5 volts, replace auto amplifier. If voltage is as specified, check wiring harness between water temperature sensor and auto amplifier. Repair or replace as necessary. If wiring is okay, replace auto amplifier.

Sunload Sensor Input Voltage

1. Turn ignition off. Remove sunload sensor from instrument panel. Disconnect sunload sensor harness connector.
2. Turn ignition switch to ON position. Measure voltage between sunload sensor harness connector Gray wire terminal and chassis ground.
3. If voltage reading is approximately 5 volts, check sunload sensor harness. If voltage is not as specified, check sunload sensor voltage variation.

Sunload Sensor Harness Check

1. Turn ignition off. Remove auto amplifier. See «AUTO AMPLIFIER»(/subaru/legacy/bcbjbf-1989-1994/remont/automatic-hvac-system/#ac-heater-system-automatic) under REMOVAL & INSTALLATION. Unplug auto amplifier 16-pin harness connector.
2. Check harness continuity between sunload sensor harness connector Gray wire terminal and auto amplifier terminal No. 16. (Scheme 5) Repair as necessary.
3. Check harness continuity between sunload sensor harness connector Yellow/Black wire terminal and auto amplifier terminal No. 5. (Scheme 5) Repair as necessary. If harness is okay, replace auto amplifier.

Sunload Sensor Voltage Variation Check

1. Connect sunload sensor harness connector. Connect auto amplifier harness connectors. Turn ignition on.
2. Cover sunload sensor. Measure voltage between sunload sensor harness connector Gray wire terminal and chassis ground. Voltage should be approximately 5 volts.
3. Slowly uncover sunload sensor. Ensure sunload sensor circuit voltage decreases as intensity of light increases. If sensor circuit voltage varies correctly, replace auto amplifier. If sensor circuit voltage does not vary correctly, replace sensor.

PBR Resistance Check

1. Turn ignition off. Disconnect air mix door motor harness connector. Apply 12 volts to air mix door motor connector terminal No. 6 and ground terminal No. 2. (Scheme 6)
2. Air mix door should move to COLD position. Measure resistance between air mix door motor connector terminals No. 1 and No. 3. (Scheme 6) See PBR RESISTANCE SPECIFICATIONS TABLE. PBR RESISTANCE SPECIFICATIONS Air Mix Door Motor Position Resistance (Ohms) COLD Approximately Zero HOT Approximately 3000
3. Reverse polarity of terminals No. 2 and No. 6. Air mix door should move to HOT position. Measure resistance between terminals No. 1 and No. 3. See «PBR RESISTANCE SPECIFICATIONS TABLE»(/subaru/legacy/bcbjbf-1989-1994/remont/automatic-hvac-system/#ac-heater-system-automatic).
4. If resistance readings are not as specified or air mix door does not operate correctly, replace air mix door motor. If resistance readings are as specified, check PBR circuit voltage.

PBR Circuit Voltage Check

1. Remove auto amplifier. See «AUTO AMPLIFIER»(/subaru/legacy/bcbjbf-1989-1994/remont/automatic-hvac-system/#ac-heater-system-automatic) under REMOVAL & INSTALLATION. Connect auto amplifier harness connectors.
2. Turn ignition switch to ON position. Measure voltage between auto amplifier 16-pin harness connector terminal No. 13 and chassis ground. (Scheme 5)
3. If voltage reading is approximately 5 volts, repair harness between PBR and auto amplifier. If voltage is not as specified, replace auto amplifier and recheck.

Scheme 6

Mode Door Motor Operational Check

1. Start self-diagnostic procedure. See SELF-DIAGNOSTIC SYSTEM under TROUBLE SHOOTING. Proceed to DIAGNOSTIC STEP 3.
2. Check mode door motor position as described. See ACTUATOR OPERATION SPECIFICATIONS TABLE in DIAGNOSTIC STEP 3 under TROUBLE SHOOTING. If mode door motor positioning is incorrect, check control rod.

Control Rod Check

1. While still in DIAGNOSTIC STEP 3, press DEF switch until 34 is indicated in temperature display. Disconnect mode door motor control rod from side link. (Scheme 7) Ensure side link moves smoothly.
2. Press DEF switch and cycle mode door motor through each position and ensure movement. See ACTUATOR OPERATION SPECIFICATIONS TABLE in DIAGNOSTIC STEP 3 under TROUBLE SHOOTING.
3. If mode door motor does not operate correctly, replace mode door motor. If mode door motor cycles through each position smoothly, go to next step.
4. Press DEF switch until 34 is indicated in temperature display. Reconnect mode door motor control rod to side link. Press DEF switch and ensure mode door motor turns smoothly through each position.
5. If mode door motor control rod impedes smooth operation of mode door, adjust control rod. If mode door motor control rod operation is okay, check mode door motor.

Mode Door Motor Check

1. While still in self-diagnosis diagnostic step 3, press DEF switch until 34 is indicated in temperature display. Remove 3 bolts and mode door motor from heater unit.
2. Apply 12 volts to mode door motor connector terminal No. 1 and ground terminal No. 2. (Scheme 8) Mode door motor linkage should rotate clockwise and move mode door from VENT to DEF (defrost) position.
3. Reverse polarity of terminals. Mode door motor linkage should rotate counterclockwise and move mode door from DEF (defrost) to VENT position. If mode door motor does not function as specified, replace motor.
4. Reconnect mode door motor harness connector. While still in self-diagnosis DIAGNOSTIC STEP 3, press DEF switch and check continuity between terminal No. 10 and appropriate terminals of mode door motor connector. (Scheme 8) See MODE DOOR MOTOR CONNECTOR CONTINUITY SPECIFICATIONS TABLE.
5. If mode door motor continuity is not as specified, replace mode door motor. If mode door motor continuity is okay, replace auto amplifier and recheck.

MODE DOOR MOTOR CONNECTOR CONTINUITY SPECIFICATIONS

Scheme 7

Scheme 8

Intake Door Motor Operational Check

1. Start self-diagnostic procedure. See «SELF-DIAGNOSTIC SYSTEM»(/subaru/legacy/bcbjbf-1989-1994/remont/automatic-hvac-system/#ac-heater-system-automatic__self-diagnostic-system) under TROUBLE SHOOTING. Proceed to DIAGNOSTIC STEP 3.
2. Ensure intake door motor operates correctly. See ACTUATOR OPERATION SPECIFICATIONS TABLE in DIAGNOSTIC STEP 3 under TROUBLE SHOOTING. (Scheme 9) If intake door motor does not operate correctly, check control rod.

Scheme 9

1. Disconnect control rod from intake door motor. (Scheme 10) With intake door unlocked, operate intake door lever manually. Ensure intake door moves smoothly.
2. While still in self-diagnosis DIAGNOSTIC STEP 3, press DEF switch and cycle intake door motor through each position. Ensure intake door motor operates correctly. If intake door motor does not operate correctly, check intake door motor. If intake door motor is okay, go to next step.
3. Press DEF switch until 35 is indicated in temperature display. Set intake door to CIRC position and reconnect control rod to intake door motor. (Scheme 9)and (Scheme 10). Recheck intake door motor operation.

Scheme 10

Intake Door Motor Check

1. Disconnect intake door motor harness connector. Apply 12 volts to intake door motor connector terminal No. 4 and ground terminal No. 2. (Scheme 9) Intake door motor should move to CIRC position.
2. Apply 12 volts to intake door motor connector terminal No. 4 and ground terminal No. 1. (Scheme 9) Intake door motor should move to FRESH position.
3. If intake door motor does not function as specified, replace motor. If intake door motor functions correctly, check harness between intake door motor and auto amplifier. Repair or replace as necessary. If harness is okay, replace auto amplifier.

Air Mix Door Motor Operational Check

1. Start self-diagnostic procedure. See SELF-DIAGNOSTIC SYSTEM under TROUBLE SHOOTING. Proceed to DIAGNOSTIC STEP 3.
2. By checking shaft lever positions, ensure air mix door motor operates correctly. See «ACTUATOR OPERATION SPECIFICATIONS TABLE»(/subaru/legacy/bcbjbf-1989-1994/remont/automatic-hvac-system/#ac-heater-system-automatic) in DIAGNOSTIC STEP 3 under TROUBLE SHOOTING. (Scheme 11) If air mix door motor does not operate correctly, check control rod.

Scheme 11

1. Disconnect control rod from air mix door motor. (Scheme 12) With air mix door unlocked, manually operate air mix door lever. Ensure air mix door moves smoothly. Repair as necessary.
2. While still in self-diagnosis DIAGNOSTIC STEP 3, press DEF switch and cycle air mix door motor through several full strokes in each direction.
3. Ensure air mix door motor operates fully through each stroke. If air mix door motor does not operate as specified, check air mix door motor. If air mix door motor is okay, go to next step.
4. Press DEF switch until 31 is indicated in temperature display. Set air mix door shaft lever to FULL HOT position. (Scheme 11) Reconnect control rod to air mix door motor shaft lever. (Scheme 12)

Scheme 12

Air Mix Door Motor Check

1. Disconnect air mix door motor harness connector. Apply 12 volts to air mix door motor connector terminal No. 2, and ground terminal No. 6. (Scheme 6)
2. Air mix door motor should move to FULL HOT position. (Scheme 11) Reverse polarity of air mix door motor connector terminals. Air mix door motor should move to FULL COLD position.
3. If air mix door motor does not function as specified, replace motor. If air mix door motor functions correctly, check harness and connectors between air mix door motor and auto amplifier. Repair as necessary. If harness and connectors are okay, replace auto amplifier and recheck air mix door motor.

Blower Motor Circuit Check

1. Start self-diagnostic procedure. See SELF-DIAGNOSTIC SYSTEM under TROUBLE SHOOTING. Proceed to DIAGNOSTIC STEP 3.
2. Ensure blower fan speed changes in proportion to blower motor voltage. See «ACTUATOR OPERATION SPECIFICATIONS TABLE»(/subaru/legacy/bcbjbf-1989-1994/remont/automatic-hvac-system/#ac-heater-system-automatic) in DIAGNOSTIC STEP 3 under TROUBLE SHOOTING.
3. If blower fan speed does not change correctly during normal operation but changes correctly during self-diagnostics, replace auto amplifier. If blower fan speed does not change correctly during self-diagnostics, exit self-diagnostic mode.
4. Press HI switch. (Scheme 3) If blower fan does not operate at high speed, check high relay. If blower fan operates at high speed, go to next step.
5. Press LO switch. (Scheme 3) If blower fan does not operate at low speed, check fan control amplifier. If blower fan operates at low speed, replace fan control amplifier.

High Relay Check

1. Remove high relay, located next to blower motor. Apply battery voltage and ground to coil side of relay. (Scheme 13) Ensure continuity exists between other relay terminals.
2. If continuity does not exist, replace relay. If continuity is okay, check blower motor operation.

Scheme 13

Blower Motor Operational Check

1. Disconnect blower motor harness connector. Connect 12-volts to blower motor connector Black/Red wire terminal, and ground Black/Yellow wire terminal.
2. If blower motor does not operate smoothly, replace blower motor. If blower is okay, check harness and connectors. Repair as necessary.

Fan Control Amplifier Check

1. Connect fan control amplifier harness connector, located behind dash on blower motor housing. (Scheme 14) Turn ignition on and fan off.
2. Measure voltage between fan control amplifier connector terminal No. 1 and chassis ground. (Scheme 14) If voltage reading is greater than zero, replace fan control amplifier. If voltage reading is zero, go to next step.
3. Turn ignition off. Disconnect fan control amplifier harness connector. Check for continuity between fan control amplifier connector terminals No. 2 and 4. (Scheme 14) If continuity does not exist, go to next step. If continuity exists, replace fan control amplifier.

Scheme 14

Compressor Operational Check

1. Start self-diagnostic procedure. See «SELF-DIAGNOSTIC SYSTEM»(/subaru/legacy/bcbjbf-1989-1994/remont/automatic-hvac-system/#ac-heater-system-automatic__self-diagnostic-system) under TROUBLE SHOOTING. Proceed to DIAGNOSTIC STEP 3.
2. Ensure compressor magnetic clutch switches on and off as specified when performing diagnostic step 3. See «ACTUATOR OPERATION SPECIFICATIONS TABLE»(/subaru/legacy/bcbjbf-1989-1994/remont/automatic-hvac-system/#ac-heater-system-automatic) in DIAGNOSTIC STEP 3 under TROUBLE SHOOTING.
3. If compressor clutch does not switch on and off as specified, check compressor power supply. If compressor clutch switches as specified, compressor is okay.

Compressor Power Supply Check

1. While still in self-diagnosis DIAGNOSTIC STEP 3, press DEF switch until 31, 32 or 35 is indicated in temperature display.
2. Measure voltage between compressor connector Yellow/Green wire and ground. If battery voltage does not exist, check A/C cut relay power supply. If battery voltage exists, replace compressor magnetic clutch.

A/C Cut Relay Power Supply Check

1. Disconnect A/C cut relay harness connector. Measure voltage between ground and A/C cut relay harness connector terminals No. 1 and 2. (Scheme 15)
2. If battery voltage does not exist on both terminals, repair or replace harness, connector or fuse. If battery voltage exists, check A/C relay power supply.

Scheme 15

A/C Relay Power Supply Check

1. Disconnect A/C relay. Measure voltage between chassis ground and A/C relay harness connector terminals No. 2 and 3. (Scheme 16)
2. If voltage readings are not approximately 12 volts at each terminal, replace pressure (trinary) switch. If voltage readings are as specified, check thermo amplifier power supply.

Scheme 16

Thermo Amplifier Power Supply Check

1. Disconnect thermo amplifier harness connector. Measure voltage between chassis ground and thermo control amplifier harness connector Red/Black wire.
2. If voltage reading is not approximately 12 volts, repair or replace harness or fuse. If voltage reading is as specified, check auto amplifier output voltage.

1. Turn ignition on. Press DEF switch. Disconnect auto amplifier 20-pin harness connector. Measure voltage between chassis ground and auto amplifier terminal No. 19. (Scheme 17)
2. If voltage reading is not approximately 12 volts, replace auto amplifier. If voltage reading is as specified, replace thermo amplifier.

Scheme 17

PRESSURE (TRINARY) SWITCH

1. Remove cap from high-pressure line service valve. Install manifold gauge to service valves. Disconnect pressure switch harness connector.
2. Connect ohmmeter leads to specified switch terminals. See «PRESSURE SWITCH OPERATING SPECIFICATIONS TABLE»(/subaru/legacy/bcbjbf-1989-1994/remont/automatic-hvac-system/#ac-heater-system-automatic). (Scheme 18) Run air conditioner and ensure pressure switch turns system on and off at specified pressure readings. If switch does not operate as specified, replace switch.

PRESSURE SWITCH OPERATING SPECIFICATIONS

Scheme 18

Removal & Installation

1. Remove cup holder from instrument panel. Remove 4 securing screws and remove center panel. Remove ventilation grilles, switch box, mirror control switch and height control switch (if equipped).
2. Remove 2 screws on upper side of A/C control panel. Remove 2 screws on upper side of cluster meter. Pull meter visor up and forward, and remove visor from instrument panel.
3. Remove mounting screws from auto amplifier. Disconnect auto amplifier harness connectors. To install, reverse removal procedure. Ensure no clearance exists between components.

Removal

1. Disconnect negative battery cable. Discharge A/C system using approved refrigerant recovery/recycling equipment.
2. Disconnect low-pressure and high-pressure hoses from compressor. DO NOT lose "O" rings. Plug hose ends immediately after disconnection.
3. Remove compressor belt and alternator belt covers. Remove alternator belt. Loosen idler pulley bolt, and remove compressor belt.
4. Remove alternator wiring harness. Remove compressor wiring harness. Remove lower compressor bracket. Remove compressor.

Installation

1. To install, reverse removal procedure. Tighten hose fittings to 10-14 ft. lbs. (14-20 N.m). Tighten idler pulley bolt until belt deflection is to specification. See SPECIFICATIONS table at beginning of this article.
2. After component installation is complete, evacuate air from refrigeration system. Charge A/C system with refrigerant. Inspect A/C system operation.

1. Disconnect negative battery cable. Discharge A/C system using approved refrigerant recovery/recycling equipment.
2. Remove front grille. Remove radiator support bracket and air guide. Disconnect pipe and hose connections from condenser.
3. Remove condenser securing bolts. Remove condenser through opening between radiator and radiator panel.

1. To install, reverse removal procedure. Ensure guide on lower side of condenser in inserted into hole in radiator panel.
2. Tighten upper hose fitting bolt to 10-14 ft. lbs. (14-20 N.m). Tighten all other fittings and bolts for condenser to 52-86 INCH lbs. (6-10 N.m).
3. After component installation is complete, evacuate air from refrigeration system. Charge A/C system with refrigerant. Inspect A/C system operation.

1. Disconnect negative battery cable. Disconnect wiring harness from fan motor. Loosen bolts on lower side of condenser fan shroud, and remove bolts from upper side.
2. Remove condenser fan assembly. To install, reverse removal procedure. Tighten bolts to 48-83 INCH lbs. (5.4-9.3 N.m).

1. Disconnect negative battery cable. Discharge A/C system using approved refrigerant recovery/recycling equipment. Disconnect discharge pipe, suction pipe and grommets from evaporator.
2. Remove glove box and support bracket. Disconnect wiring harness from evaporator. Disconnect drain hose from evaporator. Remove evaporator mounting bolt and nut. Remove evaporator.

Disassembly & Reassembly

1. Remove clamps and evaporator upper case. Remove thermostat from upper case. Remove thermistor from evaporator fins.
2. Disconnect expansion valve and pipe between receiver-drier and evaporator. Remove expansion valve from pipes. To reassemble, reverse disassembly procedure. Install thermistor onto evaporator fins. (Scheme 19)

Inspection

Check evaporator fins for clogging or damage. Repair or replace as necessary. To clean fins, use compressed air. DO NOT clean evaporator fins with water.

To install, reverse removal procedure. After component installation is complete, evacuate refrigeration system of air. Charge A/C system with refrigerant. Inspect A/C system operation.

Scheme 19

1. Disconnect negative battery cable. Discharge A/C system using approved refrigerant recovery/recycling equipment. Disconnect pressure switch wiring harness.
2. Disconnect pipes from receiver-drier. Remove mounting bolt and remove receiver-drier. Plug pipe connections and receiver-drier openings immediately after disconnection.

1. To install, reverse removal procedure. Tighten receiver-drier mounting bolt and pipe attaching bolt to 48-83 INCH lbs. (5.4-9.3 N.m).
2. After component installation is complete, evacuate refrigeration system of air. Charge A/C system with refrigerant. Check A/C system operation.

Automatic A/C-Heater System Wiring Diagram (1990). Scheme 20

Automatic A/C-Heater System Wiring Diagram (1991). Scheme 21

See also:
• AUTO AMPLIFIER
• SELF-DIAGNOSTIC SYSTEM