A/c-Heater System - Automatic Buick Roadmaster VIII

A/C SYSTEM SPECIFICATIONS

A/C SYSTEM SPECIFICATIONS

DESCRIPTION

SYSTEM DESCRIPTION

All air conditioning and heating functions are controlled automatically by an Electronic Control Unit (ECU) located within the A/C-heater control unit. Manual controls allow the driver to select air distribution mode and desired temperature. In addition to normal A/C system components, the system includes various motors, controls and sensors. (Scheme 1) The system includes self-diagnostic capabilities.

Scheme 1

A/C-HEATER CONTROL UNIT

The A/C-heater control unit is programmed to provide a specific air outlet mode and blower motor speed for each temperature valve position. The system can also be put into automatic operation by pressing AUTO switch. After selecting desired temperature, the entire system operates automatically.

ACTUATORS

Vacuum switching is controlled through a solenoid module. The solenoids are activated by the A/C-heater control unit. Upon solenoid activation, vacuum is directed to appropriate actuator. A/C-heater control unit switches polarity of air mix door motor for mode selection. Temperature valve position is monitored through input from feedback circuit in air mix door motor.

Temperature Sensors

Temperature sensors are thermistors that increase resistance as temperature decreases and decrease resistance as temperature increases. Resistance variation is from greater than 100,000 ohms at -40°F (-40°C) to less than 2000 ohms at 95°F (35°C).

Sunload Sensor

Sunload sensor is a reverse bias photodiode which responds to sunlight by changing resistance.

TEMPERATURE AIR VALVE (A/C-HEATER CONTROL UNIT) RECALIBRATION

If a new temperature air valve (air mix door motor) is installed or A/C-heater control unit has been disconnected, A/C-heater control unit must be recalibrated. To recalibrate unit, start engine. Operate A/C-heater system for at least 30 seconds with temperature setting at 90°F (32°C). Change temperature setting to 60°F (15°C), and operate system for at least another 30 seconds. A/C-heater control unit will now be calibrated.

TROUBLE SHOOTING

Note. Unless otherwise specified, use only a Digital Volt-Ohmmeter (DVOM) with input impedance of 10 megohms for measuring voltage while testing or trouble shooting system.

SELF-DIAGNOSTIC SYSTEM

Self-diagnostic system monitors system sensors, temperature valve position, refrigerant pressure and ECM signal. If a problem is detected, a fault code is stored in A/C-heater control unit memory. If a system fault is detected, °F/°C symbol will flash. Stored fault codes can be displayed on A/C-heater control unit display. See RETRIEVING CODES . After retrieving codes, see appropriate test procedure under TROUBLE SHOOTING .

Entering Self-Diagnostics

While pressing and holding EXT TEMP switch, press OFF switch. Fault codes will appear on graphic display. See FAULT CODE IDENTIFICATION .

FAULT CODE IDENTIFICATION

Parameter Diagnostic Mode

While in diagnostic mode, several system parameters may be checked. To enter parameter diagnostic mode, press EXT TEMP switch again. To sequence to each parameter, press blower speed (up arrow) switch or blower speed (down arrow) switch. Parameter numbers are displayed at A/C-heater control unit. See PARAMETER NUMBER IDENTIFICATION . Once parameter is selected, press AUTO switch to display parameter diagnostic value.

PARAMETER NUMBER IDENTIFICATION

EXITING DIAGNOSTIC MODE & CLEARING CODES

To exit diagnostic mode, press either AUTO or ECON switch on A/C-heater control unit. To erase stored codes from memory, press OFF switch on A/C-heater control unit. Fault Code 09 can be cleared after adding refrigerant to system by pressing OFF switch while in self-diagnostic mode. After replacing faulty component, disconnect battery to ensure complete memory clearance.

Scheme 2

1. Turn ignition off. Unplug connector at temperature air valve actuator motor. Turn ignition on. Measure voltage at Light Blue wire at motor connector. If voltage is considerably less than 5 volts, go to next step. If voltage is about 5 volts, go to step 3). If voltage is considerably more than 5 volts, temporarily substitute known good A/C-heater control unit. Retest system.
2. Turn ignition off. Unplug A/C-heater control unit connector. Check Light Blue wire for continuity between actuator motor and control unit connector pin No. 12. (Scheme 2) If continuity does not exist, repair open circuit in Light Blue wire. If continuity exists, temporarily substitute known good A/C-heater control unit. Retest system.
3. Check for continuity between Light Green/Black wire in actuator motor connector and chassis ground. If continuity exists, go to step 5). If continuity does not exist and Codes 03, 05 and/or 07 are present, go to next step. If continuity does not exist and no other codes are present, repair open circuit in Light Green/Black wire. See «WIRING DIAGRAM»(/buick/roadmaster/viii-1991-1996/remont/automatic-hvac-system/#ac-heater-system-automatic).
4. Check Light Green/Black wire for continuity between actuator motor and inside air temperature sensor and between outside air temperature sensor and sunload sensor. If continuity does not exist, repair open circuit in affected wire. If continuity exists, temporarily substitute known good A/C-heater control unit. Retest system.
5. Measure voltage between Brown/White wire in motor connector and chassis ground. If voltage is about 3 volts, replace actuator motor. If voltage is less than about 3 volts, go to next step. If voltage is greater than about 3 volts, go to step 7).
6. Unplug A/C-heater control unit connector. Check Brown/White wire for continuity between motor and connector unit pin No. 6 (Brown/White wire). See «WIRING DIAGRAM»(/buick/roadmaster/viii-1991-1996/remont/automatic-hvac-system/#ac-heater-system-automatic). If continuity does not exist, repair open circuit in Brown/White wire. If continuity exists, temporarily substitute known good A/C-heater control unit. Retest system.
7. Unplug A/C-heater control unit connector. Check for continuity between Brown/White and Light Blue wires. See «WIRING DIAGRAM»(/buick/roadmaster/viii-1991-1996/remont/automatic-hvac-system/#ac-heater-system-automatic). If continuity exists, repair short circuit between Brown/White and Light Blue wires. If continuity does not exist, temporarily substitute known good A/C-heater control unit. Retest system.

CODE 02 - TEMPERATURE AIR VALVE ACTUATOR MOTOR CIRCUIT SHORT

Note. Code 01 may also be present on fault code display.

1. Turn ignition off. Unplug temperature air valve actuator motor connector. Turn ignition on. Observe fault code display. If Code 02 is still present, go to next step. If Code 02 is no longer present, replace actuator motor.
2. Unplug A/C-heater control unit connector. Leave actuator motor disconnected. Check for continuity between Brown/White and Light Green/Black wires. If continuity exists, repair short circuit between Brown/White and Light Green/Black wires. If continuity does not exist, temporarily substitute known good A/C-heater control unit and retest system.

CODE 03 - OUTSIDE AIR TEMPERATURE SENSOR CIRCUIT OPEN

1. Turn ignition off. Unplug outside air temperature sensor, located at hood latch support. Measure sensor resistance at temperatures specified in «OUTSIDE AIR TEMPERATURE SENSOR RESISTANCE SPECIFICATIONS»(/buick/roadmaster/viii-1991-1996/remont/automatic-hvac-system/#ac-heater-system-automatic) . If sensor resistance is within 3 percent of specification, go to next step. Replace sensor if resistance is not within 3 percent of specification.
2. Reconnect outside air temperature sensor. Turn ignition on. Backprobe sensor terminal "A" (wire other than Light Green/Black) and ground. If voltmeter indicates about 5 volts, go to next step. If voltmeter indicates no voltage, go to step 4). If voltmeter indicates more or less than about 5 volts, temporarily substitute known good A/C-heater control unit. Retest system. NOTE: Both wires between A/C-heater control unit and outside air temperature sensor are Light Green/Black. Do not confuse them when checking continuity.
3. Check Light Green/Black wire for continuity between outside air temperature sensor connector and ground. If continuity does not exist, repair open circuit in Light Green/Black wire. If continuity exists, temporarily substitute known good A/C-heater control unit. Retest system.
4. Turn ignition off. Unplug A/C-heater control unit connector. Check Light Green/Black wire for continuity between A/C-heater control unit and outside air temperature sensor. If continuity does not exist, repair open circuit in Light Green/Black wire. If continuity exists, temporarily substitute known good A/C-heater control unit. Retest system.

OUTSIDE AIR TEMPERATURE SENSOR RESISTANCE SPECIFICATIONS

CODE 04 - OUTSIDE AIR TEMPERATURE SENSOR CIRCUIT SHORT

1. Turn ignition off. Unplug outside air temperature sensor, located at hood latch support. Measure sensor resistance at temperatures specified in «OUTSIDE AIR TEMPERATURE SENSOR RESISTANCE SPECIFICATIONS»(/buick/roadmaster/viii-1991-1996/remont/automatic-hvac-system/#ac-heater-system-automatic) . If sensor resistance is within 3 percent of specification, go to next step. Replace sensor if resistance is not within 3 percent of specification.
2. Reconnect outside air temperature sensor. Turn ignition on. Backprobe sensor terminal "A" (ungrounded Light Green/Black wire) and ground. If voltmeter indicates about 5 volts, go to next step. If voltmeter indicates less than about 5 volts, go to step 4). If voltmeter indicates more than about 5 volts, temporarily substitute known good A/C-heater control unit. Retest system.
3. Backprobe terminal "A" (ungrounded Light Green/Black wire) at outside air temperature sensor while shaking wiring harness and connectors between outside air temperature sensor and A/C-heater control unit. If voltage varies, repair wiring between outside air temperature sensor and A/C-heater control unit. If voltage does not vary and Code 04 still exists, temporarily substitute known good A/C-heater control unit. Retest system. NOTE: Both wires between A/C-heater control unit and outside air temperature sensor are Light Green/Black. Do not confuse them when checking continuity.
4. Turn ignition off. Unplug A/C-heater control unit connector. Check Light Green/Black wire for continuity between A/C-heater control unit and ground. If continuity exists, repair short circuit in Light Green/Black wire. If continuity does not exist, temporarily substitute known good A/C-heater control unit. Retest system.

CODE 05 - INSIDE AIR TEMPERATURE SENSOR CIRCUIT OPEN

1. Turn ignition off. Unplug inside air temperature sensor, located above glove box. Measure sensor resistance at temperatures specified in «INSIDE AIR TEMPERATURE SENSOR RESISTANCE SPECIFICATIONS»(/buick/roadmaster/viii-1991-1996/remont/automatic-hvac-system/#ac-heater-system-automatic) . If sensor resistance is within 3 percent of specification, go to next step. Replace sensor if resistance is not within 3 percent of specification.
2. Reconnect inside air temperature sensor. Turn ignition on. Backprobe sensor terminal "B" (Dark Green wire) and ground. If voltmeter indicates about 5 volts, go to next step. If voltmeter indicates no voltage, go to step 4). If voltage is more or less than about 5 volts, temporarily substitute known good A/C-heater control unit. Retest system.
3. Check Dark Green wire for continuity between inside air temperature sensor connector and ground. If continuity does not exist, repair open circuit in Light Green/Black wire. If continuity exists, temporarily substitute known good A/C-heater control unit. Retest system.
4. Turn ignition off. Unplug A/C-heater control unit connector. Check Dark Green wire for continuity between A/C-heater control unit connector and inside air temperature sensor. If continuity does not exist, repair open circuit in Dark Green wire. If continuity exists, temporarily substitute known good A/C-heater control unit. Retest system.

INSIDE AIR TEMPERATURE SENSOR RESISTANCE SPECIFICATIONS

CODE 06 - INSIDE AIR TEMPERATURE SENSOR CIRCUIT SHORT

1. Turn ignition off. Unplug inside air temperature sensor, located above glove box. Measure sensor resistance at temperatures specified in «INSIDE AIR TEMPERATURE SENSOR RESISTANCE SPECIFICATIONS»(/buick/roadmaster/viii-1991-1996/remont/automatic-hvac-system/#ac-heater-system-automatic) . If sensor resistance is within 3 percent of specification, go to next step. Replace sensor if resistance is not within 3 percent of specification.
2. Reconnect inside air temperature sensor. Turn ignition on. Backprobe sensor terminal "B" (Dark Green wire) and ground. If voltmeter indicates about 5 volts, go to next step. If voltmeter indicates less than about 5 volts, go to step 4). If voltmeter indicates more than about 5 volts, temporarily substitute known good A/C-heater control unit. Retest system.
3. Backprobe terminal "B" at inside air temperature sensor while shaking wiring harness and connectors between inside air temperature sensor and A/C-heater control unit. If voltage varies, repair wiring between inside air temperature sensor and A/C-heater control unit. If voltage does not vary and Code 06 still exists, temporarily substitute known good A/C-heater control unit. Retest system.
4. Turn ignition off. Unplug A/C control unit connector. Check Dark Green wire for continuity between A/C-heater control unit and ground. If continuity exists, repair short circuit in Dark Green wire. If continuity does not exist, temporarily substitute known good A/C-heater control unit. Retest system.

CODE 07 - SUNLOAD SENSOR CIRCUIT OPEN

1. Turn ignition off. Disconnect sunload sensor connector, located under center windshield defroster grille. Turn ignition on. Measure voltage between ground and sensor harness connector Light Blue/Black wire. If meter indicates about 5 volts, go to next step. If meter does not indicate about 5 volts, go to step 3).
2. Measure voltage between Light Blue/Black and Light Green/Black wires at sensor connector. If meter indicates about 5 volts, replace sunload sensor. If meter does not indicate about 5 volts, repair open circuit in Light Blue/Black or Light Green/Black wire between A/C-heater control unit and sensor.
3. Turn ignition off. Unplug connector from A/C control unit. Check Light Blue/Black and Light Green/Black wires between A/C-heater control unit and sensor. If continuity does not exist, repair open circuit in affected wire. If continuity exists, temporarily substitute known good A/C-heater control unit. Retest system.

CODE 08 - SUNLOAD SENSOR CIRCUIT SHORT

1. Turn ignition off. Disconnect sunload sensor connector, located under center windshield defroster grille. Turn ignition on. Measure voltage between ground and sensor harness connector Light Blue/Black wire. If meter does not indicate about 5 volts, go to next step. If meter indicates about 5 volts, temporarily substitute known good sunload sensor. Retest system.
2. Turn ignition off. Unplug A/C-heater control unit connector. Check for continuity between Light Blue/Black wire at connector and ground. If continuity exists, repair short in Light Blue/Black wire. If continuity does not exist, temporarily substitute known good sunload sensor. Retest system.

CODE 09 - LOW REFRIGERANT

1. Clear fault code. With ambient air temperature greater than 50°F (10°C), start engine. Press AUTO switch on A/C-heater control unit. Set temperature control to 60°F (15°C). Observe compressor on-off cycling times. If compressor clutch does not engage or engages for less than 10 seconds per cycle, go to next step. If compressor clutch is engaged for more than 10 seconds per cycle (normal operation), go to step 5).
2. Check for low refrigerant charge. If charge is low, check for leaks. If no leaks exist, recharge system and go to next step. If leaks exist, discharge A/C-heater system using approved refrigerant recovery/recycling equipment and repair leak. Evacuate and recharge system. Retest system.
3. Install gauge set. Operate A/C system. Compressor should cycle on at 41-51 psi (2.9-3.6 kg/cm 2 ) and off at 20-28 psi (1.4-2.0 kg/cm 2 ). If compressor cycles as specified, check for partially restricted orifice. If compressor does not cycle as specified, go to next step.
4. Connect jumper wire across high pressure cut-out switch. If compressor now cycles at specified pressures, replace high pressure cut-out switch. If compressor does not cycle as specified, replace pressure cycling switch.
5. Turn ignition off. Unplug A/C-heater control unit. Remove Light Blue wire from harness connector. Reconnect wiring to A/C-heater control unit. Operate A/C system. Measure voltage between Light Blue wire that was removed and body ground. If voltage exists at all times, repair short to voltage on Light Blue wire. If voltage does not exist at any time, repair open circuit in Light Blue wire. If voltage exists only when compressor is on, temporarily substitute known good A/C-heater control unit. Retest system.

CODE 10 - UNIVERSAL ASYNCHRONOUS RECEIVER TRANSMITTER (UART) FAILURE

1. Connect an analog voltmeter between pin "E" (Orange wire) of diagnostic connector and chassis ground. See WIRING DIAGRAM. Turn ignition on. Observe voltmeter. If voltage varies between 0.5 and 5.0 volts, go to next step. If voltage is zero, go to step 3). If voltage does not vary, replace Electronic Control Module (ECM).
2. Turn ignition off. Unplug A/C-heater control unit connector. Connect analog voltmeter between pin No. 5 (Orange wire) and ground. (Scheme 2) Turn ignition on. If voltage is zero, repair open circuit in Orange wire between A/C-heater control unit, Electronic Control Module (ECM) and diagnostic connector. If voltage varies between 0.5 and 5.0 volts, replace A/C-heater control unit.
3. Turn ignition off. Unplug Electronic Control Module (ECM) connector. Check for continuity between connector pin A8 (Orange wire) and chassis ground. (Scheme 3) If continuity does not exist, repair open circuit in Orange wire. If continuity exists, temporarily substitute known good ECM. Retest system.

Scheme 3

AIR BAG WARNING

Preliminary Checks

1. If air mix door is disturbed for any reason, recalibrate A/C-heater control unit. See ADJUSTMENTS. Ensure system has sufficient refrigerant and fault Code 09 does not appear. See SELF-DIAGNOSTIC SYSTEM under TROUBLE SHOOTING. Check ground connections for secure fit.
2. At vacuum tank, check for vacuum at Black hose from engine. If vacuum is not present, check hose for leaks and cracks. Repair hose as necessary. If vacuum is present from engine, check for vacuum at Black hose to heater and at hose to A/C-heater control unit.
3. If vacuum does not exist at heater and A/C-heater control unit, replace vacuum tank. Ensure vacuum hoses from solenoid to vacuum actuators are connected properly and in good condition.
4. If air delivery appears incorrect, check system and vacuum functions. See AUTOMATIC A/C SYSTEM FUNCTIONAL CHECK and VACUUM DIAGNOSIS.
5. If temperature of discharge air from ducts does not change when adjusting temperature setting from 60°F (15°C) to 90°F (32°C) or from 90°F (32°C) to 60°F (15°C), see DISCHARGE AIR TEMPERATURE DOES NOT CHANGE.

Automatic A/C System Functional Check

1. Perform these steps to verify A/C control system is functioning properly. If any problems are encountered, diagnose and repair them before proceeding through following steps.
2. Idle engine until it is warm. Press OFF switch on A/C-heater control unit.
3. Press AUTO switch, and set temperature setting to 60°F (15°C). Compressor should engage, blower should operate at maximum speed and engine idle speed should increase. Discharge air should become cold and flow from instrument panel outlets.
4. Press and hold blower speed (down arrow) switch. Blower speed should slow while switch is held. Blower speed is displayed while switch is pressed. Blower should operate at speed set when switch is released.
5. Press and hold blower speed (up arrow) switch. Blower speed should increase while switch is held. Blower speed is displayed while switch is pressed. Blower should operate at speed set when switch is released.
6. Press ECON switch. Compressor should turn off and engine idle speed should drop. Discharge air may become warmer and should flow from instrument panel outlets.
7. Press AUTO switch. Set temperature to 90°F (32°C). Discharge air should become warm and flow from floor outlets.
8. Set temperature to 75°F (24°C). Temperature display should drop one degree at a time until set temperature is reached. Blower speed should decrease as interior temperature approaches set temperature. A/C-heater system should maintain interior temperature at setting. Discharge air should be from instrument panel and floor outlets when temperature is near 75°F (24°C).
9. Press front defogger switch. Air should flow from windshield outlets. Press rear defogger switch. Rear window defogger grid should warm back glass. Press rear defogger switch again to turn rear defogger off.
10. Press OFF switch. Blower should shut off. If A/C-heater system functions properly, check vacuum lines. See VACUUM DIAGNOSIS.

Scheme 4

1. Turn ignition on. Measure voltage between solenoid module harness connector terminal No. 6 (Brown wire) and ground. (Scheme 4) If voltage exists, go to next step. If voltage does not exist, repair open or short to ground in Brown wire between solenoid module harness connector and fuse No. 6.
2. Press OFF switch on A/C-heater control unit. Connect test light to battery voltage, and backprobe solenoid module harness connector terminals No. 1, 2 and 3. (Scheme 4) Test light should glow at all 3 terminals. If test light does not glow at all terminals, go to next step. If test light glows at all 3 terminals, go to step 4).
3. Check for open or short to battery voltage in Light Green/Black wire (terminal No. 1), Red wire (terminal No. 2) and Purple wire (terminal No. 3) between solenoid module harness connector and A/C-heater control unit. If wires are okay, temporarily substitute a known good A/C-heater control unit. Retest system.
4. Press AUTO switch on A/C-heater control unit. Set temperature to 60°F (15°C). Using test light, backprobe between ground and solenoid module harness connector terminals No. 2, 4 and 5. (Scheme 4) If test light does not glow at any terminal, go to next step. If test light glows at all 3 terminals, go to step 6).
5. Check for short to ground in Red wire (terminal No. 2), Light Blue wire (terminal No. 4) and Tan wire (terminal No. 5) between solenoid module harness connector and A/C-heater control unit. If wires are okay, temporarily substitute known good A/C-heater control unit. Retest system.
6. Set temperature to 90°F (32°C). Connect one end of test light to battery voltage. Backprobe all solenoid module harness connector terminals individually. Test light should come on at terminals No. 1 and 3 only. If test light functions as described, go to next step. If test light does not function as described, temporarily substitute a known good A/C-heater control unit. Retest system.
7. Adjust temperature setting until bi-level indicator appears. Connect one end of test light to battery voltage. Backprobe solenoid module harness connector terminals No. 1, 3, 4 and 5. Test light should glow at terminal No. 1 only. If test light functions as described, go to next step. If test light does not function as described, temporarily substitute A/C-heater control unit. Retest system.
8. Press front defogger switch on A/C-heater control unit. Connect one end of test light to battery voltage. Backprobe all solenoid module harness connector terminals individually. Test light should glow at terminal No. 3 only. If test light functions as described, perform VACUUM DIAGNOSIS. If test light does not function as described, temporarily substitute known good A/C-heater control unit. Retest system.

Vacuum Diagnosis

1. Perform INCORRECT AIRFLOW FROM OUTLETS procedure. If A/C-heater control unit performs as specified, start engine. Measure vacuum supply at engine manifold and solenoid module side of vacuum tank. Vacuum should be equal. Turn engine off. Vacuum should hold. Replace vacuum tank if necessary.
2. Test each vacuum actuator by disconnecting vacuum hose and applying vacuum directly to actuator. Repair or replace actuators as necessary.
3. Reconnect all vacuum hoses and electrical wiring. Start engine. Cycle through operating modes of A/C-heater control unit while observing vacuum actuators. (Scheme 5) Check for vacuum to actuators by noting actuator position. When vacuum is applied, actuator should retract.
4. If any vacuum actuator retracts when it should not, replace A/C-heater control unit. If any vacuum actuator does not retract when it should, check for vacuum leaks, collapsed vacuum hoses and binding valves. Repair or replace components as necessary. If no leaks, collapsed hoses or binding valves exist, replace solenoid module.

Scheme 5

Discharge Air Temperature Does Not Change

1. Ensure no fault codes exist. See SELF-DIAGNOSTIC SYSTEM under TROUBLE SHOOTING. Ensure radiator is filled to proper level. Warm engine, and let it idle. Press OFF switch on A/C-heater control unit.
2. Connect one end of a test light to ground. Backprobe other end to solenoid module harness connector terminal No. 2. (Scheme 4) If test light glows, go to next step. If test light does not glow, check for open or short to battery voltage in Red wire between solenoid module harness connector and A/C-heater control unit. Repair wire as necessary. If no open or short to voltage exists, replace A/C-heater control unit.
3. Disconnect Gray vacuum hose at heater water valve vacuum actuator, and connect hose to vacuum gauge. Vacuum should be present with A/C-heater system off. Vacuum should not be present with A/C-heater system on automatic and set for 90°F (32°C). If vacuum is correct, go to next step. If vacuum is not correct, check hose for vacuum leak. If hose is okay, replace solenoid.
4. Check for stuck temperature valve. If valve is okay and discharge air is always cold, replace heater water valve vacuum actuator.

Check fuses No. 4, 6 and 7. Check for corrosion on connector terminals at blower motor and A/C power module. Repair components as necessary. Ensure ground connections are secure. If blower motor can be controlled in either manual or automatic mode but not both, temporarily substitute known good A/C-heater control unit. Retest system.

A/C-Heater Control Unit Appears Completely Inoperative

1. Connect test light between terminals No. 1 and 2 of A/C-heater control unit connector. (Scheme 2) If test light does not glow, go to next step. If test light glows, go to step 3).
2. Check for an open circuit or short to battery voltage in Black wire from A/C-heater control unit harness connector terminal No. 2. If Black wire is okay, check fuse No. 4. Replace fuse if necessary. If fuse No. 4 is okay, check for an open or short to ground in Orange wire between fuse No. 4 and A/C-heater control unit harness connector terminal No. 1. If Orange wire is okay, inspect seating of harness connector on A/C-heater control unit. Repair connector as necessary.
3. Turn ignition on. Connect test light between terminals "B" (Brown wire) and No. 2 (Black wire) of A/C-heater control unit connector. If test light glows, temporarily substitute known good A/C-heater control unit. Retest system. If test light does not glow, check fuse No. 6. Replace fuse if necessary. If fuse No. 6 is okay, repair open or short in Brown wire between fuse No. 6 and A/C-heater control unit harness connector.

Blower Motor Does Not Run

1. Unplug 4-pin A/C power module harness connector, located under right side of instrument panel. Connect voltmeter between ground and Gray/Black wire terminal of 4-pin harness connector. Turn ignition on. Set blower speed to lowest setting. Slowly increase blower speed to the highest setting while observing voltage. Voltage should increase with blower speed.
2. If voltage increases with blower speed, go to next step. If voltage does not increase with blower speed, check for open or short to ground in Gray/Black wire between Electronic A/C power module and A/C-heater control unit. Repair wire as necessary. If no open or short to ground exists, replace the electronic A/C-heater control unit. Retest system.
3. Unplug A/C power module 2-pin harness connector C2. Measure voltage between ground and Orange wire of Electronic A/C power module 2-pin harness connector. If battery voltage exists, go to next step. If battery voltage does not exist, check fuse No. 7. If fuse No. 7 is okay, repair open and/or short to ground in Orange wire between Electronic A/C power module harness connector and fuse No. 7.
4. Connect voltmeter between Orange wire of Electronic A/C power module 2-pin harness connector and Black wire terminal of Electronic A/C power module 4-pin harness connector. If battery voltage exists, go to next step. If battery voltage does not exist, repair open circuit in Black (ground) wire.
5. Turn ignition off. Reconnect Electronic A/C power module harness. Unplug blower motor connector. Connect voltmeter between Purple wire terminal of blower motor harness connector and ground. Turn ignition on. Set blower speed to lowest setting. Slowly increase blower speed setting while observing voltmeter. Voltage should increase with blower speed setting.
6. If voltage increases with blower speed setting, go to next step. If voltage does not increase with blower speed setting, check for open or short to ground in Purple wire between A/C-heater control unit, blower motor harness connector and Electronic A/C power module. If no opens or shorts exist, replace the Electronic A/C Power Module. Retest system.
7. Measure voltage between Orange wire terminal of A/C power module 2-pin connector and Black wire terminal of blower motor harness connector. If battery voltage exists, go to next step. If battery voltage does not exist, repair open in Black (ground) wire.
8. Check for corrosion on blower motor terminals. Repair terminals as necessary. If terminals are okay, replace blower motor.

Blower Motor Runs Constantly

1. Unplug A/C-heater control unit harness connector. Turn ignition on. If blower runs, go to next step. If blower does not run, replace and recalibrate A/C-heater control unit. See ADJUSTMENTS.
2. Turn ignition off. Unplug A/C power module 4-pin harness connector. Turn ignition on. If blower runs, repair short to power in Purple wire between A/C-heater control unit harness connector and blower motor.
3. If blower motor does not run, repair short to voltage in Gray/Black wire between A/C-heater control unit and A/C power module. If Gray/Black wire is okay, replace A/C power module. (Scheme 6)

Blower Motor Noisy

Replace blower motor.

Scheme 6

Ensure A/C-heater system is properly charged with refrigerant and fault Code 09 is not present. See SELF-DIAGNOSTIC SYSTEM under TROUBLE SHOOTING. Inspect compressor clutch connector terminals for corrosion. Repair terminals as necessary. Ensure ground connections are secure.

A/C Compressor Clutch Never Engages

1. Check for continuity between Black wire at compressor clutch connector and chassis ground. If continuity exists, go to next step. If continuity does not exist, repair open circuit in Black wire.
2. Start engine. Turn A/C on. Using a test light, backprobe Dark Green wire at compressor clutch connector. If voltage does not exist, go to next step. If voltage exists, replace compressor clutch coil.
3. Using test light, backprobe Light Blue wire at compressor control relay. If voltage does not exist, go to step 6). If voltage exists, turn engine off. Unplug Electronic Control Module (ECM) connector No. 1. Using an ohmmeter, backprobe between Light Blue wire at A/C high pressure cut-out switch and Dark Green wire at compressor clutch connector.
4. If resistance is less than 5 ohms, go to next step. If resistance is greater than 5 ohms, check for poor connection at compressor control relay, an open circuit in Dark Green wire between relay and compressor clutch and a short to ground in Dark Green/White wire between compressor control relay and ECM. See WIRING DIAGRAM. If wiring is okay, replace compressor control relay.
5. If resistance is less than 5 ohms, ECM is providing improper ground for compressor control relay. Check sensor outputs and for system fault codes. See TROUBLE SHOOTING. For more A/C compressor clutch control trouble shooting information, see A/C COMPRESSOR CLUTCH CONTROLS article in the AIR CONDITIONING & HEAT Section.
6. Backprobe Dark Blue wire at A/C high pressure cut-out switch. If voltage does not exist, go to next step. If voltage exists, check for open circuit in Light Blue wire between cut-out switch and compressor control relay. If wire is okay, replace A/C high pressure cut-out switch.
7. Backprobe Light Green wire at A/C pressure cycling switch connector. If voltage does not exist, go to next step. If voltage exists, check for open circuit in Dark Blue wire between cycling switch and A/C high pressure cut-out switch. If wire is okay, replace A/C pressure cycling switch.
8. Backprobe 2 Brown wire terminals in A/C control relay connector. If voltage exists on both wires, go to next step. If voltage does not exist on both wires, repair open circuit between control relay and fuse block. See WIRING DIAGRAM.
9. Backprobe Light Green wire at A/C control relay connector. If voltage does not exist, go to next step. If voltage exists, repair open circuit in Light Green wire between control relay and A/C pressure cycling switch.
10. Using a fused jumper wire, connect Dark Green/Yellow terminal of A/C-heater control unit to ground. If compressor clutch does not engage, check for open circuit in Dark Green/Yellow wire between A/C control relay and A/C-heater control unit. If wire is okay, replace A/C control relay. If compressor clutch engages, see A/C-HEATER CONTROL UNIT APPEARS COMPLETELY INOPERATIVE test under BLOWER CONTROLS.

A/C Compressor Clutch Always Engaged

1. Unplug A/C-heater control unit harness connector. Turn ignition on while listening for compressor clutch engagement. If compressor clutch engages, replace A/C-heater control. If compressor clutch does not engage, go to next step.
2. Remove A/C control relay at convenience center, located near driver's left knee in passenger compartment. If A/C compressor clutch does not engage, go to next step. If compressor clutch engages, check for short to ground in Dark Green/Yellow wire between A/C control relay harness connector and A/C-heater control harness connector. If no short exists, replace A/C control relay.
3. Unplug A/C pressure cycling switch harness connector. If compressor clutch still does not engage, go to next step. If compressor clutch engages, repair short to battery voltage in Light Green wire between A/C control relay and A/C pressure cycling switch.
4. Remove A/C compressor control relay, located in engine compartment. If compressor clutch engages, go to next step. If compressor clutch does not engage, repair short to ground in Dark Green wire between A/C compressor control relay, A/C clutch diode and compressor clutch.
5. Turn ignition off. Install A/C compressor control relay. Disconnect Electronic Control Module (ECM) 24-pin harness connector. Turn ignition on. If compressor clutch does not engage, temporarily substitute known good ECM. If compressor clutch engages, repair short to battery voltage in Light Blue wire between ECM 24-pin harness connector terminal B8 and A/C pressure cycling switch.

REMOVAL & INSTALLATION

Note. For removal and installation procedures not covered in this article, see MANUAL A/C-HEATER SYSTEMS article in the AIR CONDITIONING & HEAT Section.

1. Remove screws near lower edge of steering column opening filler. Remove filler. Partially lower steering column. Remove trim plate screws. Pull trim plate away from instrument panel.
2. Pull A/C-heater control unit from instrument panel enough to unplug electrical connectors. Remove A/C-heater control unit. Remove control lamps (if necessary). To install, reverse removal procedure.

A/C power module is attached to bottom of A/C module, just left of blower motor. Turn ignition off. Remove upper rear edge of passenger-side lower sound insulator. Pull sound insulator back until locator studs at forward edge are disengaged. Unplug electrical connectors. Remove A/C power module. (Scheme 6) To install, reverse removal procedure.

INSIDE AIR TEMPERATURE SENSOR

Note. Before removing any temperature sensor, record and clear fault codes stored in A/C-heater control unit memory. See SELF-DIAGNOSTIC SYSTEM under TROUBLE SHOOTING.

Remove lower steering column opening filler. Loosen nuts, and partially lower steering column. DO NOT remove bolts. Unsnap and remove trim plate. Unplug electrical harness connector and duct from sensor. Remove inside air temperature sensor. To install, reverse removal procedure.

OUTSIDE AIR TEMPERATURE SENSOR

Note. Before removing any temperature sensor, record and clear fault codes stored in A/C-heater control unit memory. See SELF-DIAGNOSTIC SYSTEM under TROUBLE SHOOTING.

Disconnect negative battery cable. Unplug sensor lead from body harness near forward left corner of engine compartment. Remove clips from radiator support brace. Remove outside air temperature sensor from radiator support. To install, reverse removal procedure. Ensure locating tab fits into hole in radiator support.

Note. Before removing sunload sensor, record and clear fault codes stored in A/C-heater control unit memory. See SELF-DIAGNOSTIC SYSTEM under TROUBLE SHOOTING.

Unsnap and remove center windshield defroster nozzle grille from upper trim pad. Twist sunload sensor counterclockwise. Pull sensor from nozzle grille. Unplug harness connector. Remove sunload sensor. To install sensor, reverse removal procedure.

TEMPERATURE AIR VALVE ACTUATOR

Removal

1. Disconnect negative battery cable. Open ashtray. Remove screws, and pull ashtray away from instrument panel. Unplug electrical connector. Remove ashtray. Remove tilt lever from steering column.
2. Remove lower steering column opening filler. Partially lower steering column. Remove trim plate screws. Pull trim plate away from instrument panel. Remove temperature air valve actuator motor from air valve shaft.

Installation

Align metal drive sleeve of temperature air valve actuator motor with flats on air valve shaft. Press actuator motor forward into position. To complete installation, reverse removal procedure.

1. Turn ignition off. Remove sound insulator. Remove vacuum manifold. Unplug hose connector for engine compartment hoses near vacuum solenoid assembly. Disconnect hose end connectors from vacuum tubes of actuators and vacuum tank.
2. Slide connector from tube while holding tab back against body of connector. Note positions and routing of hoses. Remove vacuum hose harness. To install, reverse removal procedure.

Turn ignition off. Remove sound insulator. Unplug harness connector from vacuum solenoid assembly. Separate vacuum solenoid assembly from A/C module. (Scheme 6) Disconnect vacuum hoses from module. Remove vacuum hose manifold from vacuum solenoid assembly. To install, reverse removal procedure.

TORQUE SPECIFICATIONS

TORQUE SPECIFICATIONS

Scheme 7

Automatic A/C-Heater System Wiring Diagram. Scheme 8

See also:
• RETRIEVING CODES
• TROUBLE SHOOTING
• SELF-DIAGNOSTIC SYSTEM