A/C-HEATER CONTROL PANEL
When the AUTO button is pressed and the desired temperature is selected, the A/C system operates in automatic mode to maintain temperature at the level selected. Specific function can be manually selected by pushing the appropriate button.
When fresh air setting is selected and defrost button is pressed, A/C can be used to defog windshield and windows. Pressing the ECON button puts A/C system in economy mode, operating compressor only when necessary to maintain temperature at selected level.
A/C CONTROL UNIT
The A/C control unit is located under center console. (Scheme 3). Control unit receives input signals from temperature setting, in-car temperature sensor and photo sensor. These signals are transmitted to blend-air damper motor, mode selector damper motor and blower motor control to maintain desired vehicle interior temperature.
Scheme 3
Air Inlet (Outside Air) Temperature Sensor
Mounted on blower assembly, sensor informs control unit of air temperature entering evaporator.
Coolant Temperature Sensor
Sensor is mounted on heater assembly, left of glove box. Sensor informs control unit of heater core temperature.
In-Car Temperature Sensor
Mounted on center of headliner, sensor informs control unit of actual interior temperature of vehicle.
Photo Sensor
Mounted on top right of airflow vent, sensor transmits signal to control unit based on how much sunlight is entering vehicle.
Evaporator Thermistor
Mounted in evaporator fin, thermistor informs control unit of evaporator temperature.
Potentiometer
Potentiometer is built as part of the blend-air damper motor and mode selector damper motor. Potentiometer informs control unit of damper position.
BLOWER MOTOR SPEED CONTROL
Power transistor, located behind glove box outer case, regulates blower motor speed. Signal from control unit energizes power transistor to operate blower motor at a speed required to maintain automatic setting. On high blower speed, the power transistor is by-passed and high-speed blower relay is used.
MUT Or MUT-II
Ensure ignition is off. Connect tester using the attached adapter harness. Follow instructions provided by equipment manufacturer. See TROUBLE CODE IDENTIFICATION table for cause and description.
Analog Voltmeter
- Turn ignition off. Connect voltmeter positive lead to Data Link Connector (DLC) terminal No. 7. Connect negative lead to DLC terminal No. 12 (Stealth) or No. 6 (3000GT). (Scheme 4)
- Turn ignition on. Count voltmeter sweeps to identify trouble code(s). Long sweeps identify first digit of code, and short sweeps identify second digit. A short pause separates first and second digits of code. See «TROUBLE CODE IDENTIFICATION»(ref-39057-S14688878592001011200000) table. If 2 or more codes are present, the codes will be repeatedly displayed in numerical order until ignition is turned off.
Scheme 4
| Code | Cause |
|---|---|
| 0 | Normal |
| 11 | In-Car Temp. Sensor Open Circuit |
| 12 | In-Car Temp. Sensor Short Circuit |
| 13 | Air Inlet (Outside Air) Temp. Sensor Open Circuit |
| 14 | Air Inlet (Outside Air) Temp. Sensor Short Circuit |
| 21 | Evaporator Thermistor Open Circuit |
| 22 | Evaporator Thermistor Short Circuit |
| 31 | Blend-Air Damper Potentiometer Short/Open Circuit |
| 32 | Mode Selector Damper Potentiometer Short/Open Circuit |
| 41 | Defective Blend-Air Damper Motor |
| 42 | Defective Mode Selector Damper Motor |
TROUBLE CODE IDENTIFICATION
R-12
- Park vehicle out of direct sunlight. Turn adapter valve all the way back, and install adapter valves to high-pressure and low-pressure service valves. Connect manifold gauge to service valves. Tighten adapter valve handle, and open service valves.
- Start engine. Set mode selector lever at face position, and temperature control lever at maximum cool setting. Move air selector lever to recirculated air setting. Turn A/C on. Operate blower fan in high speed. Adjust engine speed to 1000 RPM with compressor clutch engaged. Close all doors and windows. Ensure hood is open. NOTE: If clutch cycles, take temperature reading before clutch disengages.
- Insert thermometer in center vent. Run engine for 20 minutes, and note discharge air temperature on thermometer. Ensure discharge temperature and system low-side and high-side pressures are within specification. See «A/C SYSTEM PERFORMANCE SPECIFICATIONS»(ref-39057-S27949380832001011200000) table.
R-134a
- Park vehicle away from direct sunlight. Close high-pressure and low-pressure valves of manifold gauge. Connect manifold gauge to A/C system. Start engine.
- Set mode selector lever at face position. Set temperature control lever at maximum cool setting, and air selector lever at recirculated air setting. Turn A/C on. Operate blower fan in high speed. Adjust engine speed to 1000 RPM with compressor clutch engaged. Close all doors and windows. Ensure hood is open. NOTE: If clutch cycles, take temperature reading before clutch disengages.
- Insert thermometer in center vent. Run engine for 20 minutes, and note discharge air temperature on thermometer. Ensure discharge temperature and system low-side and high-side pressures are within specification. See A/C SYSTEM PERFORMANCE SPECIFICATIONS table.
| Application | (1) Specification |
|---|---|
| Discharge Air Temperature | 33.8-39.2°F (1.0-4.0°C) |
| Low-Side Pressure | 18.5-27.5 psi (1.30-1.93 kg/cm 2 ) |
| High-Side Pressure | 110.9-118.1 psi (7.80-8.30 kg/cm 2 ) |
| (1) Specification listed with ambient temperature at 80°F (27°C). | |
| (1) | Specification listed with ambient temperature at 80°F (27°C). |
A/C SYSTEM PERFORMANCE SPECIFICATIONS
- Connect ohmmeter to in-car temperature sensor terminals. Measure resistance value of sensor at room temperature of 77°F (25°C). Resistance should be approximately 4000 ohms. Replace sensor if resistance is not as specified.
- To check in-car temperature sensor circuit, measure voltage between A/C control unit terminal No. 66 and ground, at room temperature of 77°F (25°C). see scheme 3 Voltage should be 2.3-2.9 volts.
- If voltage is not as specified, check circuit on harness between sensor and A/C control unit. Check for poor connection at A/C control unit connector, or check for a defective A/C control unit. Repair or replace as necessary.
AIR INLET TEMPERATURE SENSOR
- Connect ohmmeter to air inlet temperature sensor terminals. Measure sensor resistance at room temperature of 77°F (25°C). Resistance should be approximately 4000 ohms. Replace sensor if resistance is not as specified.
- To check sensor circuit, measure voltage between A/C control unit terminal No. 55 and ground, at room temperature of 77°F (25°C). see scheme 3 Voltage should be 2.2-2.8 volts.
- If voltage is not as specified, check circuit on harness between sensor and A/C control unit. Check for poor connection at A/C control unit connector, or check for a defective A/C control unit. Repair or replace as necessary.
- Disconnect coolant temperature sensor connector. Connect ohmmeter to coolant temperature sensor terminals. Check sensor continuity with coolant temperature at 73-87°F (23-31°C). Continuity should be present. If continuity does not exist, replace coolant temperature sensor.
- To check sensor circuit, measure voltage between A/C control unit terminal No. 59 and ground, with temperature less than 122°F (50°C). Voltage should be 12 volts with ignition off. Measure voltage between control unit terminal No. 59 and ground, with temperature greater than 122°F (50°C). Ensure voltage is zero volts with ignition on.
- If voltage is not as specified, check harness circuit between coolant temperature sensor and A/C control unit. Check for poor connection at A/C control unit connector, or check for a defective A/C control unit. Repair or replace as necessary.
- Using ohmmeter, check resistance of thermistor at indicated temperatures. See «EVAPORATOR THERMISTOR RESISTANCE»(ref-39057-S34311570222001011200000) table. Replace evaporator thermistor if resistance largely deviates from specified value.
- To check thermistor circuit, measure voltage between A/C control unit terminal No. 67 and ground, with temperature at 77°F (25°C). see scheme 3 Voltage should be 2.3-2.9 volts.
- If voltage is not as specified, check harness circuit between evaporator thermistor and A/C control unit. Check for poor connection at A/C control unit connector, or check for a defective A/C control unit. Repair or replace as necessary.
| Water Temperature °F (°C) | Ohms |
|---|---|
| 77 (25) | 3980-4120 |
| 104 (40) | 2210-2350 |
| (1) With thermistor submerged in warm water at specified temperatures for minimum of one minute. | |
| (1) | With thermistor submerged in warm water at specified temperatures for minimum of one minute. |
EVAPORATOR THERMISTOR RESISTANCE (1)
FRESH/RECIRCULATED AIR DAMPER MOTOR
| CAUTION | DO NOT continue to apply battery voltage when damper has completed its travel or if motor fails to rotate. |
- Ensure damper is not in recirculated or fresh air position. Disconnect fresh/recirculated air damper motor connector. Apply battery voltage to motor connector. (Scheme 5) Ensure motor rotates when battery voltage is applied.
- Reverse battery polarity on motor connector. Ensure motor rotates in the opposite direction. If motor does not function as specified, check wiring or replace defective motor.
Scheme 5
BLEND-AIR DAMPER MOTOR
| CAUTION | DO NOT continue to apply battery voltage when damper has completed its travel or if motor fails to rotate. |
- Ensure damper is not in maximum hot or maximum cool position. Disconnect blend-air damper motor connector. Apply battery voltage to motor connector Red/Green wire and Black/White wire terminals. Ensure motor rotates when battery voltage is applied.
- Reverse battery polarity on motor connector. Ensure motor rotates in the opposite direction. If motor does not function as specified, check wiring or replace defective motor.
BLEND-AIR DAMPER POTENTIOMETER
- Connect ohmmeter between motor connector Blue/Green wire and Blue/White wire terminals. Resistance should gradually change as damper is moved from maximum hot to maximum cool position.
- Resistance should be 200 ohms at maximum hot position, and 4800 ohms at maximum cool position. Replace blend-air damper motor if resistance is not as specified.
- To check potentiometer circuit, set damper to maximum cool position. Measure voltage between A/C control unit connector terminal No. 56 and ground. see scheme 3 Voltage should be 0.1-0.3 volt. Measure voltage between control unit terminal No. 56 and ground with damper at maximum hot position. Voltage should be 4.7-5.0 volts.
- If voltage is not as specified, check harness circuit between air mix damper potentiometer and A/C control unit. Check for poor connection at A/C control unit connector, or check for a defective A/C control unit. Repair or replace as necessary.
MODE SELECTOR DAMPER MOTOR
| CAUTION | DO NOT continue to apply battery voltage when damper has completed its travel, or if motor does not rotate. |
- Ensure damper is not in defrost or face position. Disconnect mode selector damper motor connector. Apply battery voltage to motor connector Red/Yellow wire and Green/Blue wire terminals. Ensure motor rotates when battery voltage is applied.
- Reverse battery polarity on motor connector. Motor should rotate in the opposite direction. If motor does not function as specified, check wiring or replace defective motor.
MODE SELECTOR DAMPER POTENTIOMETER
- Connect ohmmeter between damper motor connector Blue/Green wire and Blue/White wire terminals. Resistance should gradually change as damper is moved from defrost to face position.
- Resistance should be 200 ohms at defrost position, and 4800 ohms at face position. Replace mode selector damper motor if resistance is not as specified.
- To check potentiometer circuit, set damper to face position. Measure voltage between A/C control unit connector terminal No. 57 and ground. see scheme 3 Voltage should be 0.1-0.3 volt. Measure voltage between control unit terminal No. 57 and ground with damper at defrost position. Voltage should be 4.7-5.0 volts.
- If voltage is not as specified, check harness circuit between outlet selector damper potentiometer and A/C control unit. Check for poor connection at A/C control unit connector, or check for a defective A/C control unit. Repair or replace as necessary.