A/C Switch
Pressing A/C button will operate the A/C system when temperatures are more than 34°F (1°C). When cooling with maximum power, the system automatically recirculates inside air (with little fresh air admission) and the defroster outlets close automatically.
Air Distribution Levers
Air distribution levers control airflow to either face, footwell or defroster air outlets. (Scheme 9) The lever on the top of control panel controls airflow to windshield defroster outlets and front side windows. The lever in the middle of control panel controls airflow to instrument panel grille openings and center console grille. The lever on the bottom of control panel controls lower footwell outlets.
Scheme 9
Blower Motor Control
The center rotating switch on the right side of control panel controls blower motor operation with 4 settings; OFF, low, medium and high blower speeds.
Left & Right Side Temperature Controls
The left and right rotating switches on right side of control panel allows separate temperature settings for left and right side of vehicle interior.
Rear Window Defogger Switch
Pressing the defrost button will activate the rear window defogger.
Recirculating Air Mode Switch
Pressing the recirculated air button will stop fresh air intake and recirculate inside air. Automatic temperature control will continue to operate.
Pressing A/C button will operate the A/C system when temperatures are more than 34°F (1°C). When cooling with maximum power, the system automatically recirculates inside air (with little fresh air admission) and the defroster outlets close automatically.
Air Distribution Controls
Air distribution buttons control airflow to either footwell outlets or to face and footwell outlets. (Scheme 10) The AUTO button in the middle controls airflow to windshield defroster outlets, front side windows, instrument panel grille openings, center console grille, and footwell outlets.
Scheme 10
Blower Motor Wheel
One rotary potentiometer wheel is used to control air volume to driver's and passenger's sides. System is switched off in the "0" position, except in defrost mode. The blower will run using about 4.5 volts in the first detent of the blower control wheel. In the maximum position, a relay is activated and the blower operates at full battery voltage.
Pressing the defrost button will activate the automatic defrost mode. This program has priority over other programs (including indicator lights of previously operated buttons). Entire air volume is supplied to defroster nozzles. Pressing button a second time resumes program selected before defrost was activated.
Pressing the recirculated air button will stop fresh air intake and recirculate inside air. Automatic temperature control will continue to operate.
Temperature Controls
A rotary potentiometer is integrated in each temperature control wheel for temperature adjustment on driver's and passenger's sides. The regulation of both sides is interrupted in the maximum and minimum positions of the left (driver's) temperature control wheel. If the left temperature control wheel is placed at its maximum heat position, 82°F (28°C), both water valves will open.
AIR DISTRIBUTION MOTORS
Distribution of air is controlled by a series of flaps that are actuated by stepper motors.
AUXILIARY WATER PUMP
An auxiliary (electric type) water pump is installed in the water inlets of the heater cores. This ensures a sufficient water flow rate through the heater cores even at low engine speeds. Pump is located in rear of engine compartment below heater valve.
EVAPORATOR TEMPERATURE SENSOR
After A/C button is pushed, compressor is controlled by an evaporator temperature sensor, which will switch the compressor off once evaporator temperatures fall to less than 35°F (1.6°C). This prevents evaporator freezing. When evaporator temperature reaches more than 37°F (2.7°C), compressor is turned on.
HEATER CORE SENSORS
The heater core sensors are located behind the 2 heater cores. These sensors constantly monitor heater core temperatures. The auxiliary control circuits use signals from sensors to regulate temperature.
INSIDE TEMPERATURE SENSOR
The inside temperature sensor, located in the control panel, must be ventilated to measure actual inside temperatures. Ventilation is accomplished with a radial-type blower (located in rear section of control panel).
OUTSIDE TEMPERATURE SENSOR
Outside temperatures are monitored by an outside sensor, located in the air inlet opening for the blower. This sensor (a resistor) is attached on the right side of inlet opening and is a one-piece wire harness lead.
Outside sensor causes a slight increase in passenger compartment temperature by switching the inside temperatures a few degrees above current outside temperature. If outside temperature is 32°F (0°C), inside temperature is increased about 9°F (-13°C). If outside temperature is 68°F (20°C), inside temperature is increased about 2°F (-17°C).
High Pressure Switch
A high pressure switch (located on receiver-drier) disengages compressor clutch when system pressures have increased to 441 psi (31 kg/cm 2 ). Compressor will reactivate when system pressures have decreased to 338 psi (23 kg/cm 2 ).
Low Pressure Switch
A low pressure switch (located on receiver-drier) disengages the compressor clutch when system pressures have decreased to less than 17 psi (1.2 kg/cm 2 ). Compressor will reactivate when system pressures have increased to 32 psi (2.2 kg/cm 2 ).
Medium Pressure Switch
Depending upon system pressures, a medium pressure switch causes the auxiliary (condenser) fan to operate in speed 2 when system pressures are at 257 psi (18 kg/cm 2 ). Auxiliary (condenser) fan operation will shut off when system pressures stabilize at 213 psi (15 kg/cm 2 ).
WATER VALVES
Two electromagnetic water valves control the water flow rate through the heater cores. Both valves are operated by ground pulses from the A/C-heater control unit. Each valve is spring-loaded open and powered closed for safety reasons. When the driver's side temperature control wheel is in either the maximum heating or minimum cooling positions, it has priority over the position of the passenger's side temperature control wheel. This is accomplished through electronics in the A/C-heater control unit and final stage switch, which is part of the circuit.
PIN VOLTAGE CHARTS (IHKR SYSTEM)
Pin voltage charts are supplied to reduce diagnostic time. Checking pin voltages at the A/C-heater control unit determines whether it is receiving and transmitting proper voltage signals. Charts may also help determine if A/C-heater control unit wiring harness has a short or open circuit. See appropriate A/C-HEATER CONTROL UNIT PIN ASSIGNMENTS table.
| Pin No. (1) | Function/Description | Signal Type Or Voltage Value |
|---|---|---|
| 1 | Electronics | Ground Circuit |
| 3 | Inside Temp. Sensor | 1.7-3.4 Volts At 50-104°F (10-40°C) |
| 4 | Nominal Air Flow Value | 0.6-4.0 Volts |
| 5 | Left Nominal Temp. Value | 0.5-4.2 Volts At 61-90°F (16-32°C) |
| 6 | Right Nominal Temp. Value | 0.5-4.2 Volts At 61-90°F (16-32°C) |
| 9 | Auxiliary Fan Signal | Zero Volts (On) ; 12 Volts (Off) |
| 10 | Electronics | Ground Circuit |
| 12 & 13 | Control Unit Reference Signal (Terminal No. 30) | 12 Volts |
| 15 | Right Water Valve Activation | 0-100% (0-12 Volts) |
| 18 | Independent Ventilation (Terminal No. 15) | 12 Volts |
| 22 | Left Water Valve Activation | 0-100% (0-12 Volts) |
| 23 | Control Unit Reference Signal | 12 Volts (Term. No. 30) |
| 25 | Terminal No. 61 (Unloader Relay) | Zero Volts (Engine Off) ; 12 Volts Engine Running |
| 26 | Terminal No. 30H | 12 Volts (When Starting) |
| (1) Pin assignments not listed are not used. | ||
| (1) | Pin assignments not listed are not used. |
A/C-HEATER CONTROL UNIT PIN ASSIGNMENTS (BLACK CONNECTOR)
| Pin No. (1) | Function/Description | Signal Type Or Voltage Value |
|---|---|---|
| 1 & 2 | Air Recirculation Flap Motor Reference Signal | 11 Volts |
| 6-9 | Footwell Flap Motor Activation | 0-100% (11 Volts When Motor Is Off) |
| 10-13 | Fresh Air Flap Motor Activation | 0-100% (11 Volts When Motor Is Off) |
| 14 | Control Knobs Reference Signal | 5 Volts |
| 15 | Diagnostic Initiation Line (RxD) | Input Signal |
| 16 | Diagnostic Data Line (TxD) | Output Signal |
| 18 | Switching Unit Sensor Fan Activation | Zero Volts (Ignition On) ; (2) 12 Volts (Ignition Off) |
| 19 | Auxiliary Water Pump Activation Relay | Ground Circuit |
| 20 | Rear Window Defogger Relay | Zero Volts (On) ; 12 Volts (Off) |
| 22 | A/C Compressor Activation (DME Control Unit (3) ) | Zero Volts (On) ; 12 Volts (Off) |
| 23-26 | Mixing Flap Motor Activation | 0-82% (Vent Flap Switch Off) ; 100% (Vent Flap Switch On) 11 Volts (Motor Off) |
| (1) Pin assignments not listed are not used. (2) Reading is obtained after ignition is off for 3 minutes. (3) Digital engine electronics. | ||
| (1) | Pin assignments not listed are not used. |
| (2) | Reading is obtained after ignition is off for 3 minutes. |
| (3) | Digital engine electronics. |
A/C-HEATER CONTROL UNIT PIN ASSIGNMENTS (BLUE CONNECTOR)
| Pin No. (1) | Function/Description | Signal Type Or Voltage Value |
|---|---|---|
| 2 | Right Heater Temp. Sensor | (2) 0.7-4.3 Volts At 32-194°F (0-90°C) |
| 3 | Left Heater Temp. Sensor | (2) 0.7-4.3 Volts At 32-194°F (0-90°C) |
| 4 | Outside Temp. Sensor | (2) 0.5-4.5 Volts At -32-104°F (-40-40°C) |
| 5 | Evaporator Temp. Sensor | (2) 1.6-3.4 Volts At 5-79°F (-5-26°C) |
| 6 | Nominal Mixing Value | 1.6-2.7 Volts; 0-100% |
| 7 | Independent Ventilation | Zero Volts (On) ;11 Volts (Off) |
| 8 | Vehicle Speed Signal | Input Signal |
| 10 | Independent Heating | Zero Volts (On) ;11 Volts (Off) |
| 12 | Terminal 58K | 12 Volts (Lights On) |
| 13 | Indicator Lt. Voltage Supply | 10 Volts (Lights Off) ; 4 Volts (Lights On/Indicator Light On) ; 6 Volts (Lights On/Indicator Light Off) |
| 14 | Air Distribution Control Reference Signal | 4.7 Volts |
| 15 | Control Knobs & Inside Temp. Sensor | Ground Circuit |
| 16 | Temperature Sensors | Ground Circuit |
| 17 | Air Distribution Control | Ground Circuit |
| 18 | Switches & Indicator Lights | Ground Circuit |
| 20 | A/C Push Button | Zero Volts (On) ;10 Volts (Off) |
| 21 | Air Recirculation Push Button | Zero Volts (On) ;10 Volts (Off) |
| 22 | Rear Window Defogger Push Button | Zero Volts (On) ;10 Volts (Off) |
| 23 | A/C Indicator Light | 2.7 Volts (LED On/Lights Off) ; 8.9 Volts (LED Off/Lights Off) |
| 24 | Rear Window Defogger Indicator Light | 2.7 Volts (LED On/Lights Off) ; 8.9 Volts (LED Off/Lights Off) |
| 25 | Air Recirculation Indicator Light | 2.7 Volts (LED On/Lights Off) ; 8.9 Volts (LED Off/Lights Off) |
| 26 | Air Recirculation Control Indicator Light | 2.7 Volts (LED On/Lights Off) ; 8.9 Volts (LED Off/Lights Off) |
| (1) Pin assignments not listed are not used. (2) Reading should be 5 volts with temperature sensor disconnected. | ||
| (1) | Pin assignments not listed are not used. |
| (2) | Reading should be 5 volts with temperature sensor disconnected. |
A/C-HEATER CONTROL UNIT PIN ASSIGNMENTS (WHITE CONNECTOR)
BLOWER MOTOR
| Application | Specification |
|---|---|
| Testing Voltage | 13 Volts |
| Operating Voltage | 9-15 Volts |
| Current Consumption | (1) 12 Amps |
| Maximum Speed | 3600-4000 |
| Axial Play | (2) 0.04" (1.0 mm) |
| (1) Approximately. (2) Maximum allowable. | |
| (1) | Approximately. |
| (2) | Maximum allowable. |
BLOWER MOTOR TEST SPECIFICATIONS
| Temperature - F° (C°) | K/ohms |
|---|---|
| 23 (-5) | 11.4-11.9 |
| 32 (0) | 8.8-9.2 |
| 41 (5) | 6.8-7.2 |
| 50 (10) | 5.3-5.6 |
| 59 (15) | 4.2-4.5 |
| 68 (20) | 3.3-3.6 |
| 77 (25) | 2.6-2.9 |
| 86 (30) | 2.1-2.3 |
| 95 (35) | 1.7-1.9 |
EVAPORATOR TEMPERATURE SENSOR SPECIFICATIONS
HEATER CORE TEMPERATURE SENSOR
| Temperature - F° (C°) | K/ohms |
|---|---|
| 4 (-20) | 84.39-109.61 |
| 14 (-10) | 48.58-62.09 |
| 32 (0) | 28.89-36.40 |
| 68 (20) | 11.13-13.83 |
| 140 (60) | 2.19-2.78 |
| 212 (100) | 0.58-0.77 |
HEATER CORE TEMPERATURE SENSOR SPECIFICATIONS
| Temperature - F° (C°) | K/ohms |
|---|---|
| 32 (0) | 2.69-3.46 |
| 50 (10) | 1.74-2.11 |
| 68 (20) | 1.15-1.32 |
| 77 (25) | 0.95-1.05 |
| 86 (30) | 0.76-0.87 |
| 104 (40) | 0.49-0.60 |
OUTSIDE TEMPERATURE SENSOR SPECIFICATIONS
INSTRUMENT PANEL
| WARNING | To avoid injury from accidental air bag deployment, for 1989-91 vehicles, read and carefully follow all SERVICE PRECAUTIONS and DISABLING & ACTIVATING AIR BAG SYSTEM procedures in AIR BAG RESTRAINT SYSTEM article. For 1992 vehicles, read and carefully follow all SERVICE PRECAUTIONS and DISABLING & ACTIVATING AIR BAG SYSTEM procedures in AIR BAG RESTRAINT SYSTEM article. For 1993 vehicles, read and carefully follow all SERVICE PRECAUTIONS and DISABLING & ACTIVATING AIR BAG SYSTEM procedures in AIR BAG RESTRAINT SYSTEM article. For 1994 vehicles, read and carefully follow all SERVICE PRECAUTIONS and DISABLING & ACTIVATING AIR BAG SYSTEM procedures in AIR BAG RESTRAINT SYSTEM article. For 1995 vehicles, read and carefully follow all SERVICE PRECAUTIONS and DISABLING & ACTIVATING AIR BAG SYSTEM procedures in AIR BAG RESTRAINT SYSTEM article. |