DESCRIPTION
| CAUTION | When discharging air conditioning system, use only approved refrigerant recovery/recycling equipment. Make every attempt to avoid discharging refrigerant into the atmosphere. |
The climate control automatic air conditioning system is of the cycling clutch orifice type. It is designed to cycle the A/C system on and off to maintain desired cooling and to prevent evaporator icing.
The climate control system automatically controls vehicle interior temperature. Both heating and cooling systems are controlled by the Body Computer Module (BCM) by operation of mode doors.
The BCM provides central control over all components in the climate control system. BCM monitors the system switches and sensors. Based upon these inputs, along with the program instructions within the computer memory, the BCM calculates the proper outputs to operate the climate control system.
This system is basically a blend air system. Air enters the vehicle through the inlet air door controlled by a vacuum actuator. Intake air moves through the evaporator core and then passes through the air mix door. The air mix door controls vehicle interior temperature by regulating the amount of cooled air and/or the amount of heated air to be mixed or blended together to give the desired interior vehicle temperature.
The control panel is a Cathode Ray Tube (CRT). Laid over the viewing screen is a transparent, pressure sensitive film. In this film are sections, or key pads which are actually small switches.
The display and the function of the CRT can be changed from one system to another. These system function displays are known as pages. To make an operation change to the climate control system, the climate control page must be brought to the CRT screen. (Scheme 1)
The other main components that comprise the climate control system are the Electronic Control Module (ECM), programmer, power module, temperature sensors, Heat Vent Air Conditioning (HVAC) module and the refrigeration system.
Scheme 1
OPERATION
The climate control system automatically regulates and maintains the selected in-car temperatures from maximum "COOL" 60°F 16°C) to maximum "HEAT" 90°F (32°C).
To select a new climate control mode or temperature level first bring the climate control page to the CRT screen. Then press the appropriate key pad on the screen. (Scheme 2)
BLOWER FAN CONTROL OPERATION
These key pads on the climate control page of the CRT control fan speed operation. When the "AUTO" key pad is selected, the blower fan will operate automatically (based on various inputs to the system) to obtain and keep the desired comfort level.
In the "HI" mode, the fan will operate in a fixed high speed with no automatic function. This is also an override of the automatic mode, and will continue until a new blower mode is selected. In the LO" mode, the blower will operate in a fixed low speed and automatic function is overridden.
When "DEF" mode is selected, from either the CRT or right switch assembly, high fan speed is automatically selected if the outside temperature is above freezing 32°F (0°C).
To eliminate entry of snow to the vehicle, when outside temperatures are below freezing 32°F (0°C), fan speed will be limited to low until the engine warms up.
If "LO" blower speed is selected before "DEF", fan speed will stay at low. If "HI" blower speed is selected before "DEF", the fan mode will change to the "AUTO" selection. If "AUTO" fan is selected before "DEF", the fan will stay in "AUTO" selection. Once in AUTO", fan speed will be at low until engine warms up, at which time the normal automatic fan speed will resume.
When in "DEF" mode, whether outside temperature is above or below freezing, touching a new fan speed key pad will override the system and go to the new fan speed selected.
TEMPERATURE & MODE SETTINGS OPERATION
To make a temperature change press the "WARM" or "COOL" key pad until the desired temperature is displayed. When a temperature of 65°F (18°C) is selected with the "COOL" mode, the system goes to maximum cooling. This will continue until another temperature setting is selected. Cooling cannot occur if the mode selected is "OFF", ECON", or "HEATER" as the A/C compressor will not run in these modes.
If 85°F (29°C) is selected and the "WARM" key pad is pressed at the same time. The system goes to maximum heat and will control the warmest air delivery possible for the selected mode.
"OFF" Setting
In this setting the system will not let the fan blower motor or A/C compressor run. The system will still try to reach the temperature selected.
"HEATER" Setting
In this setting the system will not let the A/C compressor run. It will adjust to the temperature selected. However, it cannot cool the car colder than outside air temperatures. This setting also forces all air out of the module to the floor, and all incoming air is from outside. The only automatic operation in this mode is regulating temperature door position and fan speed.
"ECON" Setting
In this setting the system will not let the A/C compressor run. It will adjust to the temperature selected. This setting is automatic in that it determines blower speed and air outlet positions by different inputs.
All incoming air into the module is from outside. Whether cooling or heating, air will enter the passenger compartment from one of the following positions: All out the floor vents, split between floor vents and defroster registers, split between the floor vents and A/C registers or all out the A/C registers.
"AUTO" Setting
In this setting everything is controlled automatically. The system will automatically adjust to the temperature selected. Depending on the heating or cooling requirement, air will enter the passenger compartment from one of the following positions: All out the floor vents, split between the floor vents and defroster registers, split between the floor vents and A/C registers or all out the A/C registers.
"BI-LEVEL" Setting
In this setting all system functions are automatic. The only difference between this mode and the "AUTO" mode, is all output air is delivered evenly through the floor vents and the dashboard registers.
"DEF" Setting
In this setting, the blower will run as described in the BLOWER FAN CONTROL "LO", "AUTO", "HI" section of this article. All air will exit the defroster registers and the system will work automatically as the A/C compressor and the air inlet position are both functional.
When exiting the "DEF" mode by selecting another mode on the CRT screen, the blower fan speed will stay at the speed it was set at before the new mode was selected. When exiting the "DEF" mode from the right switch assembly, "AUTO" mode and "AUTO" fan speed will automatically be selected.
"REAR DEFOG" Setting
If the vehicle is equipped with a rear defogger, the "REAR DEF" switch is located on the right switch panel. When this key pad is pushed the Instrument Panel Cluster (IPC) sends a signal to the BCM through the data circuit, and the BCM begins a 10 minute timer. Next, the BCM sends a signal to the programmer through the data circuit.
The programmer grounds a circuit to the rear defogger relay which supplies current to the defogger grids on the back glass. The first press of the key pad energizes the relay for 10 minutes. The second, consecutive activation of the key pad energizes the relay for an additional 5 minute period, or until the ignition is cycled off.
TEMPERATURE SENSOR INPUT OPERATIONS
There are 6 different temperatures monitored by the BCM to control the climate control system. These temperature values are sent to the BCM via thermistors which decrease in resistance as they get hotter.
In-Car Temperature Sensor
This sensor is located under the upper trim cover. A small amount of in-car air is drawn into the sensor housing and over the thermistor. The air movement is accomplished by using an aspirator mounted on the top of the HVAC module.
Airflow from the HVAC module creates a slight vacuum at one end of the aspirator. This vacuum draws in-car air through the temperature sensor housing. The resistance value of the sensor is sent to the BCM and used in climate control calculations.
Outside Temperature Sensor
This sensor is located at rear of radiator grille, in a protective housing. A temperature memory feature is used in the BCM outside temperature sensor programming to help provide greater accuracy under engine restart conditions.
If engine coolant is less than 50°F (10°C) above the outside temperature sensor reading, the actual sensed outside temperature is displayed. If engine coolant is greater than 50°F (10°C) above the sensed reading, memorized outside temperature is displayed. This is the previous temperature sensed when the engine was last running.
At speeds below 20 MPH, the BCM limits the displayed temperature value to an increase of one degree every 100 seconds. This compensates for false high temperature readings during heavy traffic or extended idle.
At speeds between 20 to 45 MPH, the outside temperature display is allowed to increase but only after a built-in 2 minute sensor cool down time delay. At speeds over 45 MPH there is no time delay.
Coolant Temperature Sensor
The coolant temperature sensor is located in an intake manifold coolant passage. Its resistance is monitored by the ECM which in turn sends the coolant temperature value to the BCM over the data circuit.
A/C High Side Temperature Sensor
The high side sensor is located in the high pressure refrigerant line between the condenser and orifice tube. By monitoring the refrigerant temperature, the BCM can determine the pressure based upon the pressure-temperature relationship of R-12.
A/C Low Side Temperature Sensor
This sensor is located between the orifice tube and evaporator in the low pressure refrigerant line. The BCM monitors this sensor to determine the low side pressure by the same method as the A/C high side temperature sensor.
Sunload Sensor
The sunload sensor is located under defroster grille at base of windshield. This sensor is a thermistor type and senses heat load of sun on vehicle interior. The BCM uses this sunload value and compares it to in-car temperature to determine how much cooling is necessary to maintain selected interior temperature.
LOW REFRIGERANT PRESSURE SWITCH OPERATION
The low refrigerant pressure switch is located in the low pressure refrigerant line. This switch is of the normally open type, and closes under pressure. When closed, this switch allows the ignition circuit to feed the compressor clutch relay. If the pressure drops below 2-8 psi (.2-.7 kg/cm 2 ), the switch opens the ignition circuit to the relay, shutting the system off. Also, there is a circuit which monitors the state of this switch for diagnostic purposes.
POWER STEERING CUT-OUT SWITCH OPERATION
The power steering cut-out switch is located in the power steering pressure line. It is of the normally closed type, and allows the ignition circuit to feed the compressor clutch relay. If for some reason the system pressure exceeds 300 psi (21 kg/cm 2 ) the switch will open the ignition circuit to the relay. Also, there is a circuit to the ECM which monitors the state of this switch for diagnostic purposes.
PROGRAMMER OPERATION
The programmer is located behind glove compartment, attached to the HVAC module. It can be identified by the electrical and vacuum connectors attached to it. Contained within the programmer are circuits which control many of the various climate control systems.
These circuits respond to the BCM data signals, and provide controls for temperature regulation. This is done by a small DC motor that adjusts the air mix door position to blend cold and warm air. The motor provides position feedback signal to the BCM which monitors actual door position.
These circuits also respond to the BCM data signals to operate 4 vacuum solenoids mounted within the programmer. These solenoids control vacuum to 3 vacuum actuators, which control the air inlet door, A/C-defrost door and a 2 position actuator for the up-down door.
The programmer circuits also receive a blower motor signal from the BCM which transfers it to the blower control power module for blower speed operation. These circuits also receive a blower feedback signal used to regulate actual blower speed and voltage.
The programmer also provides a control for the rear defogger. When the programmer receives a rear defogger signal, it provides a ground to activate the rear defogger relay.
AIR MIX DOOR LINKAGE OPERATION
This linkage consists of a plastic crank arm integral with the output shaft of the programmer, a serrated nylon retainer and a threaded rod. One end is fastened to the air mix door and the other end is retained by the serrations in the nylon retainer to the plastic crank arm. The programmer positions the air mix door with this rod when the BCM sends the appropriate signal.
BLOWER CONTROL-A/C COMPRESSOR CLUTCH POWER MODULE OPERATION
The power module provides the appropriate power and control to the compressor clutch and blower motor. It is located on the top of the evaporator assembly. The programmer sends a blower signal to the power module where it is amplified proportionally to the input voltage, then sent to the blower. The power module is transistorized, and provides variable blower speeds. A large heat sink is attached to the power module and protrudes into the evaporator air stream as a means of cooling.
The power module also receives a drive signal from the ECM, which is used to engage the A/C compressor relay. The BCM controls the cycling of the clutch based upon various input signals. The BCM signals the ECM to engage and disengage the clutch on the data circuit.
PROGRAM NUMBER DESCRIPTION
The program number is a numerical index as to the amount of heating or cooling required to meet the desired in-car temperature. There are 4 variables which determine this number: Set temperature of the CRT, outside temperature, in-car temperature and sunload sensor. The program number controls the blower speed, air inlet and outlet doors, and is also a factor in determining air mix door position.
This number is calculated by the BCM by comparing the in-car temperature with the set temperature, and adjusting the result to reflect the outside air temperature and sunload.
This program number is calculated frequently to take into account changes in in-car temperature. When the in-car temperature reaches the set temperature, the system is in equilibrium and the BCM strives to keep the program number at this point.
The program number is displayed as a number between 0 and 99. A low program number calls for cooling, a high program number calls for heating. The program number can be observed while the system is in the diagnostic mode. Also, when in this mode, the technician can override the program number to observe the effect on system operation.
AIR MIX DOOR POSITION OPERATION
The BCM needs to know 3 things before it can calculate the air mix door position: Temperature of the heater output air, temperature of the air conditioned air and the temperature that the delivered air should be. The BCM uses the coolant temperature to predict the temperature of the heated air, and the average low side temperature to predict the temperature of the conditioned air. If the A/C compressor is not working, the BCM uses the outside air temperature rather than the low side temperature signal.
The program number tells the BCM how hot or cold the delivered air should be. By monitoring a feedback potentiometer on the programmer motor, the BCM commands the programmer to move the door until the desired position is achieved.
COMPRESSOR CLUTCH CONTROL OPERATION
The compressor clutch is controlled by the BCM through the ECM. Inputs to the ECM are as follows: BCM data, power steering cut-out switch, engine coolant temperature, engine RPM and throttle position sensor.
Inputs to the BCM are as follows: ECM data, CRT setting, outside temperature, in-car temperature, sunload temperature, vehicle speed, low refrigerant pressure switch, A/C high side temperature and A/C low side temperature.
When all inputs to the BCM are within calibrated values the BCM signals the ECM on the data line to allow compressor clutch engagement. A voltage signal is then sent to the power module by the ECM. The power module then completes the path to ground and engages the A/C compressor clutch relay.
The A/C compressor clutch control will only engage the compressor clutch under the following parameters: Climate control set to "A/C", "AUTO", "BI-LEVEL", "DEF", or outside temperatures above 45°F (7°C). Once engaged, compressor clutch engagement time is controlled by the BCM as described below.
Extended Compressor Operation At Idle
Smoother idle conditions are obtained by increasing the minimum clutch delay time to about 45 seconds whenever the vehicle speed drops below 15 MPH. This mode is disabled above 17 MPH.
Normal Compressor On Time
When the vehicle operates above 17 MPH, a minimum delay time from 2 to 6 seconds is begun before the BCM will allow the clutch to disengage.
After 2 to 6 seconds, the BCM will disengage the compressor clutch only if low side temperature is below 30°F (1°C). After being disengaged, BCM waits for low side to reach a temperature between 45-50°F (7-10°C) and then repeats the cycle.
During compressor on time, there are 7 conditions which will cause BCM to disengage A/C compressor clutch. The 7 conditions are: A/C low pressure switch open, A/C low side temperature below 0°F 18°C), A/C high side temperature above 200°F (126°C), coolant temperature above 259°F (126°C), wide open throttle signal from ECM or power steering cut-out switch open.
Under all conditions, except wide open throttle signal, the compressor will stay disengaged only as long as condition exists. The wide open throttle signal only disengages the compressor clutch for a maximum of 20 seconds.
IDLE SPEED CONTROL OPERATION
To minimize the effects of compressor operation on engine idle, ECM modifies the engine idle RPM during A/C operation. When ECM receives a compressor engagement signal, it will determine if inputs are within the calibrated area before engaging A/C clutch. If ECM determines inputs are not within specifications, it will make an adjustment to the idle air control and then engage A/C compressor clutch to compensate for increased engine load.
"LOW REFRIGERANT" MESSAGE OPERATION
When operating A/C compressor clutch, BCM monitors system inputs for low refrigerant charge. If system charge should fall below one third its capacity, BCM will display the climate control problem page on CRT screen to warn operator, and store a diagnostic trouble code in memory.
COLD PURGE OPERATION
Cold purge will operate in any mode, except "DEF" or "OFF", when coolant temperature is below 28°F (-2°C). During cold purge, the blower will be off and any airflow will be directed to front defroster registers to keep breath humidity off windshield. Cold purge will be discontinued when the program number would result in cooling, or coolant temperature is above 110°F (43°C). If either of these conditions exist within 3 minutes of start-up, BCM will automatically resume normal purge control.
NORMAL PURGE OPERATION
If the system is turned on in any mode except "DEF" or OFF", when the program number would not result in cooling and the conditions for cold purge do not exist, normal purge is activated.
During normal purge, blower is turned off and any airflow is directed to heater registers with bleed air to A/C registers. To remove all moist air from ducts, the blower will only run at low speed for several seconds prior to normal operation.
Scheme 2
ADJUSTMENTS
Note. See TROUBLE SHOOTING charts at end of this article before attempting any adjustments.
TROUBLE SHOOTING
Note. Also see MANUAL A/C TROUBLE SHOOTING charts in this section.
PRELIMINARY CHECKS/PROCEDURES
- Check to see if the "SERVICE ENGINE SOON" light is working. If this light fails to light when the ignition is turned on and the engine is not running, the problem could be in the power supply circuits to these systems. The self-diagnostic check will lead to the appropriate trouble shooting chart.
- Can "SERVICE MODE" be accessed? If CRT is not operable, self-diagnostics are not possible. In this case, "Self-Diagnostic" check will lead to the appropriate trouble shooting chart.
- Is there a service code displayed? If a trouble code is identified using self-diagnostics, a problem has been detected by the system which can be corrected following the appropriately numbered fault code. Codes with the prefix "E" are ECM codes. Codes with the prefix "B" or "C" are BCM codes.
- Do a visual check of the entire system. Check the suspected wiring and components. Be sure to inspect hoses that are difficult to see beneath the compressor, generator, etc. Inspect all the related wiring for disconnects, burned or chafed spots, pinched wires or contact with sharp edges or hot exhaust manifolds.
USING SELF-DIAGNOSTICS
The various inputs to the BCM combine with program instructions within system memory to provide accurate control over many subsystems involved. When a subsystem circuit exceeds preprogrammed limits, a system malfunction is indicated and the BCM provides certain backup functions known as failsoft. A typical failsoft action would be the substitution of a fixed input value when a sensor is detected to be open or shorted.
To access and control the self-diagnostic features, use the CRT. On the CRT, a 22 character display area is used to display diagnostic information. This is part of "SERVICE MODE" page. The CRT is used to enter diagnostics and access "Service Diagnostic Routines". The Cathode Ray Tube Controller (CRTC) controls the CRT display. It interprets switches touched on the CRT, and passes this information along to BCM on the data circuit.
ENTERING SELF-DIAGNOSTICS
Turn the ignition on. Touch the "OFF" and "WARM" key pads on the CRT climate control page simultaneously and hold until a double beep" is heard or a page entitled "SERVICE MODE" appears on the screen. (Scheme 3)
Scheme 3
Note. Operating vehicle in "SERVICE MODE" for extended time periods without engine running can cause battery drain and/or possibly related false diagnostic information.
TROUBLE CODE DISPLAY
After "SERVICE MODE" is entered any trouble codes stored in computer memory will be displayed. ECM codes will be displayed first. If no ECM codes are stored, the CRT will display "NO ECM CODES" for approximately 2 seconds.
After the ECM codes have been displayed the BCM codes will be displayed. BCM codes will also be accompanied by "CURRENT" or HISTORY". "HISTORY" indicates that the failure was not present when last tested, "CURRENT" indicates the fault still exists. This type of information helps in the diagnosis of intermittent problems. If no BCM codes are present, the BCM will display the "NO BCM CODES" message.
Trouble codes for both the ECM and BCM will be displayed in numerical succession of lowest too highest numbered code.
Note. Because this article only covers climate control system, ECM codes and their descriptions are not supplied.
| Code | Circuit Affected |
|---|---|
| B110 | Outside Temp. Sensor |
| B111 | A/C Hi Side Temperature Sensor |
| B112 | A/C Lo Side Temperature Sensor |
| B113 | In-Car Temperature Sensor |
| B114 | Sunload Temperature Sensor |
| B119 | Twilight Photocell |
| B120 | Twilight Delay Pot |
| B121 | Twilight Enable Switch |
| B122 | Panel Lamp Dimming Pot |
| B123 | Courtesy Light Switch |
| B124 | Vehicle Speed Sensor (VSS) |
| B132 | Oil Pressure Sensor |
| B140 | Phone |
| B332 | Compass |
| B334 | ECM Data |
| B335 | CRTC Data |
| B336 | Instrument Panel Cluster (IPC) Data |
| B337 | Programmer Data |
| B339 | Radio Data |
| B410 | Charging System |
| B411 | Battery Low |
| B412 | Battery High |
| B418 | Crank |
| B420 | Relays |
| B440 | Air Mix Door |
| B446 | Low Refrigerant Warning |
| B447 | Very Low Refrigerant Problem |
| B448 | Low Refrigerant Pressure |
| B449 | A/C High Temp. |
| B450 | Coolant High Temperature |
| B552 | BCM Memory Reset |
| B556 | E(2) Prom |
| B660 | Cruise (Not In Drive) |
| B663 | Cruise (Speed Difference) |
| B664 | Cruise (Acceleration) |
| B667 | Cruise (Switch Shorted) |
| B671 | Cruise (Position Sensor) |
| B672 | Cruise (Vent Solenoid) |
| B673 | Cruise (Vacuum Solenoid) |
| C331 | Tape Deck |
| C339 | Radio Data |
| C553 | CRTC Memory Reset |
| C710 | CRT Switching |
BCM DIAGNOSTIC CODES
USING CLIMATE CONTROL IN SERVICE MODE
When in "SERVICE MODE", the climate control system will continue to operate in the setting it was in prior to "SERVICE MODE". Also, during "SERVICE MODE" operation, climate control can be operated the same as normal by touching climate control border key pad and calling up climate control page.
To get back to "SERVICE MODE" page, touch border key pad marked diagnostics. The climate control and diagnostic border key pads are the only 2 border key pads that will operate in "SERVICE MODE".
After trouble codes have been displayed, "SERVICE MODE" can be used to perform several tests on different systems one at a time. A specific system may be selected for testing, or a segment check can be performed.
System Selection
Following trouble code display, the first available system will be displayed, such as ECM. When making system selections there are 3 available alternatives. (Scheme 4)
- Pressing "LEVEL" key pad will stop system selection process and return to beginning of trouble code sequence.
- Pressing "NO" key pad will display next available system selection.
- Pressing "YES" key pad will select the displayed system for testing.
Test Type Selection
Having selected a system, the first available test type will be displayed. When making selection of test type there are 3 available test type alternatives. (Scheme 4)
- Pressing "LEVEL" key pad will stop test type selection and return display to next available system selection.
- Pressing "NO" key pad will display next available test type for selected system. This allows all test type step choices to be considered.
- Pressing "YES" key pad will select displayed test type. Here, display will either indicate that selected test type is in progress or the first of several specific tests will appear. If "NO DEVICES" appear, no test is available.
Test Selection
Selection of the "DATA", "INPUTS", "OUTPUTS" or "OVERRIDE" test types will result in the first available test being displayed. If dashes appear, this test is not allowed with engine running. Shut engine off and begin again.
Four characters of the display will contain a test code to identify selection. The first 2 are letters which identify the system and test type. For example, the letters ED stand for ECM DATA. The last 2 characters numerically identify the test. For example, ED01 stands for ECM DATA for throttle position. See DATA DISPLAY CODES in this article. When selecting these tests 3 alternatives are available. (Scheme 4)
- Pressing "LEVEL" key pad will stop test selection process and return display to next test type for selected system.
- Pressing "NO" key pad will display the next smaller test number. If lowest number is already displayed, the highest number will then be displayed.
- Pressing "YES" key pad will display next larger test number for selected test type. If this key pad is touched and is already at highest number, the lowest number will then appear.
Scheme 4
"CODE RESET" Selection
If "CODE RESET" test type is selected, it will result in the message "CODES CLEAR" being displayed with the selected system name above. This message appears for 3 seconds to indicate that all stored trouble codes have been erased from memory. After this 3 second interval, system will automatically return to next available test type for selected system.
Instrument Panel Cluster (IPC) Segment Check
When ignition is on and vehicle is in park, pressing "TEST" button on the IPC will cause IPC to sequentially illuminate and blank all segments and telltales in the instrument cluster. This may help to determine if all bulbs or segments of IPC are out or always on. To make this check easier, the "TEST" button on IPC may be pressed when in test mode at the system select level, and will cause the segment test to run 10 times slower than when not in "SERVICE MODE".
EXITING SELF-DIAGNOSTICS
To get out of "SERVICE MODE", repeatedly press "LEVEL" key pad until "SERVICE MODE" page disappears, or turn the ignition off.
BCM DATA DISPLAY CODE DESCRIPTIONS
When trouble shooting, the data displays can be used to compare the vehicle with problems, with a vehicle that is functioning properly. The following is a brief summary of each parameter.
Code BD20
The command blower voltage is read in volts from 0 to system voltage
Code BD21
The coolant temperature is displayed in degrees Celsius (from -40° to 151°C). These values are obtained from the ECM. If there is a failure, failsoft will respond.
Code BD22
The commanded air mix door position is displayed in a percentage. A value close to 0 percent represents a cold air mix and a value close to 100 percent represents a warm air mix door.
Code BD23
The actual air mix door position is displayed in a percentage. This value should follow the commanded air mix door position (BD22), except when the door is commanded beyond its mechanical limits.
Code BD24
The air delivery mode is displayed as a number from 0-10. Each number is a code which represents the following air delivery modes.
| Number | Mode |
|---|---|
| 0 | Automatic A/C With Maximum Recirculated Air |
| 1 | Automatic A/C |
| 2 | Automatic Bi-Level |
| 3 | Automatic Heater/Defrost |
| 4 | Automatic Heater |
| 5 | Off |
| 6 | Normal Purge |
| 7 | Cold Purge |
| 8 | Forced Defrost |
| 9 | Forced Heater |
| 10 | Forced Bi-Level |
AIR DELIVERY MODES
Code BD25
The in-car temperature is displayed in degrees Celsius (from -40° to 102°C).
Code BD26
The actual outside temperature is displayed in degrees Celsius (from -40° to 93°C). This value represents actual sensor temperature without any alterations.
Code BD27
The high side temperature is displayed in degrees Celsius (from -40° to 215°C).
Code BD28
The low side temperature is displayed in degrees Celsius (from -40° to 93°C).
Code BD32
The sunload temperature sensor is displayed in degrees Celsius (from -10° to 102°C).
Code BD40
The actual fuel level is read in gallons between 0 and 25.5. This value is actual fuel level and is not affected by features to eliminate slosh affects.
Code BD42
The dimming pot is displayed in a percentage. A value close to 0 percent represents maximum dimming. A value close to 100 percent represents maximum brightness.
Code BD43
The twilight delay pot is displayed in a percentage. A value close to 0 percent represents minimum delay time. A value close to 100 percent represents maximum delay time.
Code BD44
The twilight photocell is displayed in a percentage. A value close to 0 percent represents daylight. A value close to 100 percent represents darkness.
Code BD45
The phone mode is displayed as a number from 0 to 7. Each number is a code which represents the different phone modes
Code BD50
Battery voltage is read in volts (between 0 and 25.5 volts).
Code BD51
The alternator field is displayed in a percentage. A value close to 0 percent represents minimum regulator on time. A value close to 100 percent represent maximum regulator on time.
Code BD60
The vehicle speed is displayed in miles per hour (from 0 to 159 MPH).
Code BD61
The engine speed is displayed in RPM (from 0 to 6375 RPM).
Code BD70
The cruise control servo position is displayed in a percentage from 0 to 100. A value close to 0 percent represents rest position and a value close to 100 percent represents wide open throttle.
Code BD71
The oil pressure sensor is displayed in pounds per square inch.
Code BD90
The option content No. 1 is displayed as a number from 0 to 255. For complete information, refer to appropriate article in the COMPUTER ENG CONTROL section.
Code BD91
The option content No. 2 is displayed as a number from 0 to 255. For complete information, refer to appropriate article in the COMPUTER ENG CONTROL section.
Code BD92
The option content No. 3 is displayed as a number. For complete information, refer to the appropriate article in the COMPUTER ENG CONTROL section.
Code BD98
The ignition cycle value is the number of times that the ignition has been cycled off since a BCM trouble code was last detected. After 50 ignition cycles without any malfunction, all BCM codes are cleared.
Code BD99
The BCM PROM identification is displayed as a number, up to four digits. This can be used to determine if the proper PROM was installed in the BCM.
INPUT DISPLAYS
When trouble shooting a malfunction, the ECM, BCM, or IPC input display can be used to determine if the switched inputs are properly interpreted. When one of the input tests is selected, the state of that device is displayed as "HI" or "LO". Basically, "HI" or LO" represent the input terminal voltage for that circuit.
Also, the display indicates if the input changed state since it was last tested. If a change occurred, an "X" will appear next to the "HI" - "LO" indicator. If a change did not occur, an "O" will remain displayed. The "X" will only appear once per selected input.
USING OUTPUT DISPLAYS
When trouble shooting a malfunction, the ECM and BCM output cycling can be actuated regardless of the inputs and normal program instructions. Once a test in outputs is selected, except for ECM, the test will display "HI" or "LO" for 3 seconds in each state to indicate the command and output terminal voltage.
USING OVERRIDE DISPLAYS
When trouble shooting a malfunction, the BCM override feature allows testing of certain system functions regardless of normal program instructions. Upon selecting a test, that selections current operation will be represented as a percentage of its full range. This value will be displayed on the CRT below the "LEVEL" key pad.
Pressing the key pads above or below "OVERRIDE" on the CRT begins the override. When in override, pressing the key pad above OVERRIDE" increases the value, while pressing the key pad below decreases the value. Normal program control can be achieved in three ways: Selection of another override test will cancel the current override, selection of another system will cancel the current override or overriding the value beyond the values given to that particular system.
The override feature, or test type, is unique in that any other test type within the selected system may be active at the same time. After selection of an override test, pressing the "EXIT" key pad will allow selection of another test type, yet the CRT will continue to display the selected override. When selecting another test or type, and then pressing the key pads above or below OVERRIDE", it is possible to monitor the effect of the override on different vehicle parameters.
USING SNAPSHOT DISPLAY
Selection of the "SNAPSHOT" test type while in the BCM system level will allow the recall of up to 3 values recorded at one time for later reference of malfunction codes. see scheme 5
Scheme 5
CRT TESTING
Testing of the CRT can only be accomplished with the use of the CRT Tester (J-34914). This tester is used to isolate faults between the CRT, Cathode Ray Tube Controller (CRTC) and wiring. Substituting the tester in place of the CRTC verifies the integrity of the picture tube and switch circuitry that make up the CRT. By connecting the tester directly to the CRT, it can be checked out as a unit.
After the CRT has been checked out, connecting the tester to the vehicle harness determines if the fault is in the wiring or the CRTC. The tester runs through an automatic test, and then allows individual switch tests.
Pressing the "RESET" button on the tester initiates the automatic test sequence. After the CRT has warmed up, a test pattern is displayed which outlines the 25 key pads on the screen. If this pattern is not displayed, replace the CRT.
When the automatic test sequence is complete, the tester is ready for individual switch tests. This test indicates whether there is a problem with one of the CRT's hard or soft keys. To test these switches press the desired switch key pad to be tested. If the CRT beeps", the switch is okay, if the CRT does not "beep" the switch is faulty.
If the CRT checks out okay, check the wiring by connecting the tester to the CRT to CRTC wiring harness. Now, repeat the CRT, and switch tests. This will determine if the CRTC is faulty, or there is a wiring problem.
SYSTEM CHECK CHART
Review SELF-DIAGNOSTICS in this article before proceeding with CLIMATE CONTROL SYSTEM CHECK.
System Check Flow Chart. Scheme 6
CHART 1, LOW REFRIGERANT PRESSURE CODES B446, B447, B448
If A/C system refrigerant charge should fall below one third capacity, BCM will detect this condition and display a driver warning message. BCM determines refrigerant charge via low side temperature sensor and low pressure switch. If a low refrigerant charge is detected, BCM will store a Code B446, B447 or B448.
Note. Test numbers refer to test numbers on diagnostic charts.
- BCM input value BI08 displays the voltage state of circuit at BCM.
- This step checks if open circuit reading is due to circuit or switch.
- This step checks if fault is on ignition side or BCM side of switch circuit.
- This step checks if fault is due to pressure switch or a low refrigerant charge
Low Refrigerant Pressure Flow Chart. Scheme 7
CHART A, LOW REFRIGERANT PRESSURE CODES B446, B447, B448
Chart 1 determined that fault is not in the low refrigerant pressure switch circuit.
Note. Test numbers refer to test numbers on diagnostic charts.
- This test determines if A/C low pressure switch opens while A/C compressor is running. If BI08 remains high during compressor engagement, the system is low on refrigerant charge.
- This step checks if the switch is opening due to a low refrigerant pressure or a faulty switch.
Chart A, Low Refrigerant Pressure Flow Chart. Scheme 8
CHART 2, COMPRESSOR WILL NOT ENGAGE
The A/C compressor clutch is supplied voltage from the 10 amp A/C fuse, through a relay which is grounded by the ECM.
Note. Test numbers refer to test numbers on diagnostic charts.
- This step checks if the low side temperature sensor is responding properly.
- This step checks if fault is in the control to relay or the control to A/C clutch.
- This step checks if fault is in feed wire to the relay.
- This step checks if fault is in the control of the relay, or relay.
- This step checks if fault is due to an open or short in circuit No. 762, or short in ECM.
- This step checks if fault is due to open in circuit No. 50C to relay, or electrical feed to A/C clutch.
- This step checks if fault is due to A/C clutch or A/C power and ground circuits
Chart 2, Compressor Will Not Engage Flow Chart. Scheme 9
CHART 3, COMPRESSOR ALWAYS ENGAGED TEST
The A/C compressor clutch is supplied voltage from the 10 amp A/C fuse, through a relay which is grounded by the ECM.
Note. Test numbers refer to test numbers on diagnostic charts.
- This step checks if fault is due to mechanical binding of A/C clutch, grounded control signal or faulty ECM.
- This step checks if fault is due to mechanical binding of A/C clutch, or faulty circuits.
Chart 3, Compressor Always Engaged Flow Chart. Scheme 10
CHART 4, HIGH BLOWER SPEED ONLY FLOW CHART
Based on a signal from BCM, the programmer sends a variable voltage signal to the power module. The power module then amplifies the signal and sends signal to blower motor. The programmer monitors blower voltage and adjusts signal to achieve proper blower speed.
Note. Test numbers refer to test numbers on diagnostic charts.
- This step checks if fault is due to faulty feedback signal, or faulty blower signal.
- This step checks if fault is due to programmer, including terminal contacts or open in signal circuit, including BCM.
Chart 4, High Blower Speed Only Flow Chart. Scheme 11
CHART 5, NO BLOWER OPERATION TEST
Based on a signal from BCM, the programmer sends a variable voltage signal to the power module. The power module then amplifies the signal and sends signal to blower motor. The programmer monitors blower voltage and adjusts signal to achieve proper blower speed.
Note. Test numbers refer to test numbers on diagnostic charts.
- This step checks if fault is due to blower signal circuit to programmer, or circuits used by blower control.
- This step checks if fault in control is due to short in circuit No. 754, including programmer and circuits.
- This step checks if fault in control is due to open in circuit No. 754, or rest of control circuits.
- This step checks if fault is due to open in blower motor ground, including blower motor and control circuits.
- This step checks if fault in blower control is due to open in power module feed or short in blower motor feed, including terminal contact and excessive blower motor current draw.
- This step checks if fault in blower motor is due to short in circuit No. 760, programmer or BCM.
Chart 5, No Blower Operation Flow Chart. Scheme 12
CHART 6, AIRFLOW FROM WRONG DUCT TEST
The BCM will direct the blended air in one of several air delivery modes. While side window outlets receive air during all modes, the other outlets are directed air by commanding the programmer to energize specific vacuum valves feeding the appropriate combination of mode valve actuators. The BCM determines the proper air delivery mode based on current program number and control panel setting.
Note. Test numbers refer to test numbers on diagnostic charts.
- Verifies commanded valve position so actual air delivery can be checked.
- This step checks if fault is due to vacuum source or distribution of vacuum.
- This step checks if fault is due to vacuum circuit leaks, stuck valves or faulty programmer.
Chart 6, Airflow From Wrong Duct Flow Chart. Scheme 13
CHART 7, INSUFFICIENT HEAT AT MAXIMUM HEATING TEST
Note. Step numbers are for air mix valve adjustment (if required).
- Remove glove compartment to gain access to programmer.
- Lift straight up on air mix valve link to release it from programmer arm.
- Turn on ignition and select maximum heat. Wait for programmer arm to stop moving.
- Manually pull air mix valve link toward passenger door until it hits the mechanical stop.
- With both air mix valve link and programmer arm in maximum heat position, snap air mix valve link back into programmer arm.
- Visually check movement by selecting different temperature settings.
Chart 7, Insufficient Heat At Maximum Heating Flow Chart. Scheme 14
CHART 8, INSUFFICIENT COOLING AT MAXIMUM COOLING TEST
Note. Step numbers are for air mix valve adjustment (if required).
- Remove glove compartment to gain access to programmer.
- Lift straight up on air mix valve link to release it from programmer arm.
- Turn on ignition and select maximum heat. Wait for programmer arm to stop moving.
- Manually pull air mix valve link toward passenger door until it hits the mechanical stop.
- With both air mix valve link and programmer arm in maximum heat position, snap air mix valve link back into programmer arm.
- Visually check movement by selecting different temperature settings.
Chart 7, Insufficient Cooling At Maximum Cooling Flow Chart. Scheme 15
CHART 9, IMPROPER TEMPERATURE REGULATION TEST
Note. Test numbers refer to test numbers on diagnostic charts.
- This step checks if improper temperature regulation is due to air mix valve movement.
- This step checks if improper temperature regulation is due to poor aspirator air flow. Procedure for checking aspirator air flow is as follows: Engine running with vehicle NOT in direct sunlight. Select high blower speed and any mode EXCEPT "DEF". Hold paper strip by one end with opposite end over in-car temperature sensor air inlet. Lower paper strip until it is about 1/2" above inlet. If aspirator air flow is good, paper will be sucked down over inlet.
- This step checks accuracy of in-car temperature sensor.
- Air mix valve adjustment. Remove glove compartment to gain access to programmer. Lift straight up on air mix valve link to release it from programmer arm. Turn on ignition and select maximum heat. Wait for programmer arm to stop moving. Manually pull air mix valve link toward passenger door until it hits the mechanical stop. With both air mix valve link and programmer arm in maximum heat position, snap air mix valve link back into programmer arm. Visually check movement by selecting different temperature settings.
- This step checks if binding is due to valve or motor
Chart 9A, Air Mix Valve Adjustment Procedure. Scheme 16
Chart 9B, Improper Temperature Regulation Flow Chart. Scheme 17
CHART 10, A/C SYSTEM PERFORMANCE TEST
| Condition | Specification | |
|---|---|---|
| If Ambient Air Temperature is 70°F (20°C) | ||
| Hi Side Pressure Should Read Within +/- 20 PSI (140 kPa) of (1) | 149 PSI (1025 kPa) | |
| Lo Side Pressure Should Read +/- 2 PSI (8 kPa) of (1) | 25 PSI (170 kPa) | |
| Center A/C Outlet Temperature Should Read +/- 2°F (1°C) of (2) | 50°F (10°C) | |
| If Ambient Air Temperature is 80°F (27°C) | ||
| Hi Side Pressure Should Read Within +/- 20 PSI (140 kPa) of (1) | 178 PSI (1225 kPa) | |
| Lo Side Pressure Should Read +/- 2 PSI (8 kPa) of (1) | 27 PSI (185 kPa) | |
| Center A/C Outlet Temperature Should Read +/- 2°F (1°C) of (2) | 52°F (11°C) | |
| If Ambient Air Temperature is 90°F (32°C) | ||
| Hi Side Pressure Should Read Within +/- 20 PSI (140 kPa) of (1) | 214 PSI (1475 kPa) | |
| Lo Side Pressure Should Read +/- 2 PSI (8 kPa) of (1) | 29 PSI (200 kPa) | |
| Center A/C Outlet Temperature Should Read +/- 2°F (1°C) of (2) | 54°F (13°C) | |
| If Ambient Air Temperature is 100°F (38°C) | ||
| Hi Side Pressure Should Read Within +/- 20 PSI (140 kPa) of (1) | 272 PSI (1875 kPa) | |
| Lo Side Pressure Should Read +/- 2 PSI (8 kPa) of (1) | 33 PSI (230 kPa) | |
| Center A/C Outlet Temperature Should Read +/- 2°F (1°C) of (2) | 56°F (13°C) | |
| (1) Pressure reading taken just before Compressor Clutch release. (2) Outlet temperature will be higher on humid days. | ||
| (1) | Pressure reading taken just before Compressor Clutch release. |
| (2) | Outlet temperature will be higher on humid days. |
SYSTEM PERFORMANCE CHART
A/C LOW SIDE TEST
Note. A/C Low Side BD 28 check made after 5 minutes with engine "0ff"
| Pressure in PSI | Temperature Reading Should be Within 6° of °F (°C) |
|---|---|
| 50 | 53 (12) |
| 52 | 55 (13) |
| 54 | 57 (14) |
| 56 | 59 (15) |
| 58 | 60 (15.5) |
| 60 | 62 (16.5) |
| 62 | 64 (18) |
| 64 | 65 (18.5) |
| 66 | 67 (19.5) |
| 68 | 68 (20) |
| 70 | 70 (21) |
| 72 | 72 (22) |
| 74 | 74 (23.5) |
| 76 | 75 (24) |
| 78 | 76 (24.5) |
| 85 | 81 (27) |
| 80 | 77 (25) |
| 82 | 79 (26) |
| 88 | 83 (28.5) |
| 90 | 84 (29) |
| 92 | 85 (29.5) |
| 95 | 87 (30.5) |
| 98 | 89 (31.5) |
| 100 | 90 (32.5) |
| 102 | 91 (33) |
| 105 | 93 (34) |
| 108 | 95 (35) |
| 110 | 96 (35.5) |
| 112 | 97 (36) |
| 115 | 99 (37) |
| 118 | 101 (38.5) |
| 120 | 102 (39) |
| 125 | 104 (40) |
| 130 | 107 (42) |
| 135 | 109 (43) |
| 140 | 112 (44.5) |
FREON PRESSURE/TEMPERATURE RELATIONSHIP CHART FOR A/C LOW SIDE TEST
A/C HIGH SIDE TEST
A/C High Side BD 27 check is made with engine running at 2000 RPM.
Note. Run High Side Test only if Code B449 is set. if pressure and temperatures are both high, check for sources of excess head pressure.
If BD 27 exceeds 199°F(93°C) but pressure remains below 380 psi, sensor is out of specification.
Note. Compressor will disengage and Code B449 will set temperature sensor value exceeds 199°F.
A/C System Performance Test Flow Chart. Scheme 18
CHART 11, NO "DEF" FROM INSTRUMENT PANEL SWITCH TEST
When the "DEF" switch in the right switch assembly is pressed, a signal is sent to the Instrument Panel Cluster (IPC) by momentarily providing a ground path. The IPC then sends this message to the BCM. The BCM will then signal the programmer, as it would if "DEF" were selected on the CRT.
Note. Test numbers refer to test numbers on diagnostic charts.
- IPC input value II11 displays the voltage state of the circuit at the IPC. This can be observed with readings of "LO" or "HI" when switch is depressed. This is a momentary signal, and will display for only a short time.
- This step checks if short to ground is due to circuit or switch assembly.
- This step checks if fault was intermittent.
- This step checks if open circuit reading is due to open in circuit or switch assembly.
Chart 11, No "DEF" From Instrument Panel Switch. Scheme 19
COMPRESSOR R & I
- Disconnect negative battery cable. Discharge A/C system using approved refrigerant recovery/recycling equipment. Remove electrical connections from compressor. Remove front upper pivot bolts.
- Raise and support vehicle. Remove splash shield over compressor. Remove 2 compressor adjusting bolts. Remove coupled hose assembly from rear of compressor. Remove compressor. To install, reverse removal procedure. Evacuate and recharge A/C system.
POWER STEERING CUT-OUT SWITCH R & I
Disconnect negative battery cable. Raise and support vehicle. Remove switch and disconnect wiring. To install, reverse removal procedure.
PRESSURE CYCLING SWITCH R & I
Disconnect negative battery cable. Disconnect electrical connection at switch. Remove switch and "O" ring seal. To install, reverse removal procedure.
COMPRESSOR HIGH PRESSURE CUT-OFF SWITCH R & I
Disconnect negative battery cable. Discharge A/C system using approved refrigerant recovery/recycling equipment. Disconnect electrical connections. Remove switch. To install, reverse removal procedure. Evacuate and recharge system.
COOLING FAN A/C PRESSURE SWITCH R & I
Disconnect negative battery cable. Disconnect electrical connection at switch. Remove switch. To install, reverse removal procedure.
CONDENSER R & I
- Remove battery hold-down and battery. Discharge A/C system using approved refrigerant recovery/recycling equipment. Remove fans. Remove upper radiator support.
- Remove coolant overflow tube from radiator. Remove refrigerant lines at condenser. Remove condenser support bolts. Remove condenser. Remove refrigerant line brackets from condenser.
- To install, reverse removal procedure. Evacuate and recharge A/C system.
ORIFICE TUBE R & I
Discharge A/C system using approved refrigerant recovery/recycling equipment. Remove refrigerant lines to evaporator. Remove orifice. To install, reverse removal procedure. Evacuate and recharge A/C system.
ACCUMULATOR R & I
Disconnect negative battery cable. Discharge A/C system using approved refrigerant recovery/recycling equipment. Remove accumulator guard. Remove refrigerant line at accumulator. Remove accumulator assembly. To install, reverse removal procedure. Evacuate and recharge A/C system.
EVAPORATOR & BLOWER MODULE R & I
- Disconnect negative battery cable. Discharge A/C system using approved refrigerant recovery/recycling equipment. Remove vacuum tank and disconnect vacuum lines. Remove wiring harness protective cover. Disconnect wiring from cowl.
- Remove heater hoses and coolant pipes. Remove blower motor. Remove exhaust shield. Disconnect blower motor resistor. Remove right sound insulator. Remove heater distribution duct. Remove blower module. Remove evaporator core.
- To install, connect evaporator core to blower module, install heater distribution duct. Install right sound insulator. Connect blower motor resistor.
- Install exhaust shield. Install blower motor. Install heater hoses and coolant pipes. Reconnect wiring to cowl. Install wiring harness protective cover. Install vacuum tank and vacuum lines. Reconnect negative battery cable. Evacuate and charge A/C system.
HEATER CORE R & I
- Remove negative battery cable. Drain cooling system. Remove right sound insulator. Remove center and lower instrument panel trim plates. Remove right speaker grille and speaker.
- Remove wires and hoses from programmer. Remove programmer linkage cover and linkage. Remove programmer. Remove heater core cover. Remove splash cover to access heater hoses. Remove heater hoses. Remove heater core. To install, reverse removal procedure.
AIR INLET RECIRCULATION ACTUATOR R & I
Remove right and left sound insulators. Remove heater duct. Remove air inlet recirculation actuator. To install, reverse removal procedure.
AIR MIXTURE VALVE R & I
Remove instrument panel glove box. Remove heater duct. Remove air mixture valve lever. Remove air mixture valve through heater outlet. To install reverse removal procedure.
ACTUATOR MODE R & I
Remove right sound insulator. Remove heater duct. Remove hoses from actuator. Remove actuator. To install, reverse removal procedure.
A/C-DEFROST ACTUATOR R & I
Remove right and left sound insulators. Remove body connectors. Remove hoses from actuator. Remove actuator. To install, reverse removal procedure.
