A/c-Heater System - Automatic Cadillac Seville IV

A/C SYSTEM SPECIFICATIONS

A/C SYSTEM SPECIFICATIONS

DESCRIPTION

SYSTEM DESCRIPTION

The Electronic Climate Control (ECC) system automatically regulates and maintains the selected in-car temperature between a maximum cool of 60°F (16°C) and a maximum heat of 90°F (32°C) regardless of changes in outside air temperature.

When the outside (ambient) air temperature is greater than the selected temperature or during humid weather, the A/C compressor can be selected. This will increase passenger comfort and decrease window fogging and condensation. The Climate Control Center (CCC) is the main control for selecting in-car comfort levels. (Scheme 1)

The main components of the ECC system are the Air Conditioning Programmer (ACP), Powertrain Control Module (PCM), power module, Heating Ventilation and Air Conditioning (HVAC) module, refrigeration system and 6 temperature sensors.

The components work together to automatically control the interior temperature, air mode doors (valves) and fan speed to maintain the desired temperature.

Scheme 1

BLOWER FAN CONTROL

The blower fan control has 5 different fan-speed positions. If the blower symbol button is pressed, blower fan operates automatically between the AUTO speeds based on various system inputs.

If blower fan up arrow button is pressed once, fan speed will increase slightly. CCC will illuminate AUTO and HI indicators. Manual blower fan operation is similar to AUTO setting, except at slightly faster speeds. If blower fan up arrow button is pressed twice, fan will run at a fixed high speed and CCC will illuminate HI indicator under blower fan symbol. This overrides automatic fan-speed control.

If blower fan down button is pressed once, fan speed will decrease slightly and CCC will illuminate AUTO and LO indicators. Blower fan operation is similar to AUTO setting, except at slightly lower speeds. If blower fan down button is pressed twice, fan will run at a fixed low speed and CCC will illuminate LO indicator under blower fan symbol. This overrides automatic function.

Pressing AUTO button returns blower fan-speed control to initial automatic operation. Pressing either HI or LO buttons changes blower speed through additional AUTO HI or AUTO LO automatic operation to a fixed higher or lower speed.

TEMPERATURE SETTINGS

Temperature settings range from 60°F (16°C) to 90°F (32°C). Pressing the COOL or WARM button once will increase or decrease the set temperature by 1°F. If button is held continuously, set temperature will continue to decrease or increase until limit of 65°F (18°C) or 85°F (29°C) is reached.

Once the setting reaches 65°F (18°C), the next lowest available temperature setting is 60°F (16°C), representing maximum cooling limit. At the 85°F (29°C) setting, the next highest available temperature setting is 90°F (32°C), representing maximum heating limit. The selected temperature is displayed in the climate control panel display.

AIR DELIVERY MODE CONTROL

Note. When in SERVICE MODE of self-diagnostics, it is possible to override the following modes to observe complete operation of each mode.

OFF Mode

When OFF mode is selected, system does not allow fan blower motor or A/C compressor operation; however, system will try to reach selected temperature by regulating air-mix valve. (Scheme 2)

Because fan and A/C compressor do not operate, set temperature will probably not be reached. When in OFF mode, CCC will display only outside temperature.

ECON Mode

In this mode, A/C compressor does not operate. (Scheme 2) System will adjust to selected temperature; however, temperature inside vehicle can only be as cool as outside temperature.

In this setting, fan blower speed and air outlet positions are determined by various inputs. All incoming air into the HVAC module is from the outside. Depending on the heating or cooling requirement, air will enter the passenger compartment from floor vents, A/C registers or defroster vents.

AUTO Mode

With this setting selected, the entire system, including compressor operation, is controlled automatically by various inputs to adjust to selected temperature. (Scheme 2)

In this mode, system can use any blower speed, any air inlet position and any air outlet position to reach selected temperature. Depending on heating or cooling requirement, air will enter passenger compartment from bi-level registers and vents, upper registers only or lower vents only.

DEFOG Mode

In this setting, air is divided equally between floor and defroster vents. (Scheme 2) Compressor is allowed to cycle at lower temperatures to dehumidify the passenger compartment air.

This mode can also be entered automatically when outside air temperature is above 40°F and the windshield wipers or rear defogger are activated.

Defrost Mode

In this setting, everything is controlled automatically; most air is delivered to windshield. (Scheme 2)

Scheme 2

AIR DELIVERY SYSTEM

The HVAC assembly incorporates most of the air conditioning components into one assembly. The function of the air delivery system is to distribute airflow throughout the vehicle.

The major components of the HVAC module include air inlet valve, blower motor, evaporator core, air-mix valve, heater core, up-down valve and A/C-defogger valve. (Scheme 3)

Scheme 3

AIR CONDITIONING PROGRAMMER (ACP)

The ACP is located behind the glove box, attached to the HVAC module assembly. It can be identified by the vacuum and electrical connections attached to it. The ACP controls temperature regulation through control of the air-mix valve motor and the 4 vacuum solenoids.

The reversible air-mix valve motor adjusts the air-mix valve position through a rotary shaft which drives the air-mix valve link. The motor also provides a position sensor signal so the ACP can monitor the actual valve position.

The vacuum solenoids control the air inlet (recirculation) valve, A/C-defogger valve and the up-down valve.

The ACP calculates the proper outputs for accurate operation of climate control system based on inputs and program instructions contained within its memory. The ACP and the Powertrain Control Module (PCM) communicate over a data link to share sensor information. The PCM controls functions such as compressor clutch engagement.

The ACP is equipped with a self-diagnostic function. By depressing the appropriate buttons on the climate control panel, data messages requesting the specific diagnostic features required can be sent to ACP. If a fault is detected in the system, a trouble code is set in the ACP memory. By following specific testing procedures, system diagnosis should determine faulty component in the shortest time period.

Trouble Codes

The PCM and ACP continually monitor operating conditions for possible system malfunctions. By comparing system conditions against standard operating limits, certain circuit and component malfunctions can be detected.

If a fault is detected, a trouble code will be set in memory. See ACP TROUBLE CODES table under TESTING. Depending on the A/C-related trouble code, one of the indicator lights may also be illuminated.

Note. If a trouble code is stored in memory, the SERVICE ENGINE SOON (or SERVICE VEHICLE SOON) message on the driver information center will be illuminated.

TEMPERATURE SENSOR INPUTS

The ACP monitors 6 different temperature sensor inputs. Their temperature values are sent to the ACP via thermistor. Thermistors decrease in resistance as they get hotter.

In-Car Temperature Sensor

This sensor is located in the instrument panel, left of center. To provide accurate in-car temperature, a small amount of in-car air is drawn over the thermistor.

This air movement is accomplished through the use of an aspirator. Airflow from the HVAC module creates a slight vacuum at one end of the aspirator, which draws in-car air into the aspirator and over the thermistor.

Outside Temperature Sensor

This sensor is located to rear of radiator grille, in a small protective housing. Data from this sensor is processed by ACP and displayed on CCC.

During periods of extended idle, engine heat can build up in engine compartment. This hot air surrounds sensor and results in inaccurate readings of outside temperatures. To help eliminate these false readings, programming techniques are used to minimize unwanted temperature variations.

A temperature memory feature is used in the ACP outside temperature programming to help provide greater accuracy during engine restarts. When coolant temperature is greater than temperature sensor reading by less than 18°F (10°C), actual outside temperature is displayed. When engine coolant is greater than sensor reading by more than 18°F (10°C), previous memorized outside temperature is displayed.

At speeds of 20-45 MPH, display of outside temperature is allowed to increase after a 50-second delay period. The 50-second delay starts when vehicle speed reaches 20 MPH. At speeds greater than 45 MPH, or if the sensor reading is less than displayed value, time delay does not occur and normal display function resumes.

Coolant Temperature Sensor

The coolant temperature sensor is located in a coolant passage of the intake manifold. Its resistance value is monitored by the PCM, which in turn sends this value to the ACP for system operation calculations.

A/C High-Side Temperature Sensor

The high-side temperature sensor is located in the high-pressure refrigerant line between the condenser and orifice tube. With sensor information, the ACP can determine the A/C system pressure based on the pressure-temperature relationship of R-12 (refrigerant).

A/C Low-Side Temperature Sensor

The low-side temperature sensor is located in the low-pressure refrigerant line between the orifice tube and evaporator. With sensor information, the ACP can determine A/C system pressure based on the pressure-temperature relationship of R-12 (refrigerant).

Sunload Sensor

The sunload sensor is located under the center defroster grille, at base of windshield. This sensor senses the heat load of sun on the vehicle (lower voltage in direct sunlight and higher voltage in shade). ACP compares this value with the in-car temperature to determine the cooling necessary for maintaining selected interior temperature.

LOW REFRIGERANT PRESSURE SWITCH

The low refrigerant pressure switch is located in the low-pressure refrigerant line. When pressurized, the switch is closed and allows the ignition circuit to feed the compressor clutch coil through the compressor clutch relay.

If refrigerant pressure drops below about 10 psi (.7 kg/cm 2 ), the switch opens the ignition circuit to the clutch. The ACP monitors the switch for diagnostic purposes.

POWER MODULE

Power module controls the blower motor operation. It is located on top of the evaporator assembly in the HVAC air stream.

Power module receives the blower drive signal from the ACP and amplifies the signal to a strong output voltage proportional to the input. The power module is also transistorized and can provide variable blower speeds.

Attached to the power module is a large heat sink which protrudes into the pre-evaporator air stream as a means of dissipating the heat generated by the power module.

REAR WINDOW DEFOGGER

When the rear defogger button is pressed, a signal is sent to the ACP. The ACP grounds the defogger relay, allowing current flow to the back glass.

The ACP will turn the relay off after 10 minutes. Additional 5-minute heating periods can be selected each time the button is pressed until a new ignition cycle occurs. The defogger can be manually turned off any time during its operating cycle by pressing the rear defogger button or turning off the ignition.

PROGRAM NUMBER

The program number is calculated by the ACP to determine the amount of heating or cooling required to meet the desired in-car temperature. This number is based on set temperature, outside temperature, in-car temperature and sunload sensor.

The program number is used to determine the proper air delivery mode and blower speed and is also a factor for determining air-mix valve position. A program number of zero indicates maximum system cooling and a program number of 99 represents maximum heating.

The program number can be observed during the diagnostic mode. This feature allows the technician to manually override the calculated number to observe system operation in its entire range.

AIR-MIX VALVE POSITION

ACP determines proper air-mix valve position by monitoring the set temperature, outside air temperature, in-car air temperature, low-side temperature, sunload sensor voltage, coolant temperature, air delivery mode, engine RPM, blower speed and mix motor feedback (position).

Based on these inputs, the ACP can position the air-mix valve for appropriate blending of air through the evaporator core and heater core, depending on the current program number. By monitoring the mix motor feedback potentiometer on the programmer motor, the ACP can determine when the desired valve position is reached.

BLOWER SPEED CONTROL

For every program number and climate control panel setting, the ACP has a calculated blower motor voltage. Based on a signal sent from the ACP, a variable voltage is sent to the power module, which is then amplified and sent to the blower motor. The ACP monitors the blower motor voltage so its signal can be adjusted to achieve the desired blower speed.

Blower speed for the rear console blower is controlled manually by a direct power feed. A series of 3 resistors vary the voltage to the blower motor at each setting to control the blower speed. The ACP monitors the feedback for diagnostic purposes.

PURGE MODES

Purge modes are designed to decrease windshield fogging and increase comfort. In purge mode, airflow is redirected at reduced blower speed until conditions allow normal control. Purge modes also delay heater blower operation and prevent cool air from coming out of heater outlets.

Cold Purge

If system is turned on in any mode except defrost or OFF when coolant temperature is less than 39°F (4°C), cold purge is enabled.

During cold purge, blower is off and any airflow is directed to the front defogger vents to keep humidity off the windshield. Normal operation resumes when the program number results in cooling, or coolant temperature is greater than 97°F (36°C). If neither of these conditions appear within 1-4 minutes (depending on outside temperature), the ACP automatically resumes normal control.

Normal Purge

If the system is turned on in any mode except defrost or OFF, program number does not result in cooling or intermediate modes and cold purge conditions do not exist; in this condition, normal purge is enabled.

In normal purge, blower is turned off and airflow is directed to heater vents, with bleed air to A/C registers. To further purge moist air, ACP will operate blower at low speed for several seconds before resuming normal operation. Normal operation is resumed when the program number results in cooling or the coolant temperature is greater than 97°F (36°C).

If neither of these conditions exist within 1-4 minutes (depending on outside temperature), ACP will automatically resume normal control.

A/C Purge

If the system is turned on in any mode, the blower will operate at medium speed for 7 seconds, with air directed out of heater outlets. A/C purge will not be activated in defrost or OFF modes when the program number results in cooling or intermediate modes and conditions required for either cold or normal purge are not present.

During A/C purge, hot moist air is purged from A/C module and floor ducts while evaporator cools incoming air. ACP automatically resumes normal control of air mode delivery when A/C purge is completed.

COMPRESSOR CLUTCH CONTROL

Note. The compressor clutch circuit is equipped with an in-line diode. Diode is located on the lower right front of engine, inside engine harness.

The PCM controls the compressor clutch based on inputs to PCM and ACP. PCM inputs for compressor control consist of power steering pressure switch, throttle position sensor and inputs from ACP for outside temperature and A/C refrigerant pressure/temperature (high-side and low-side).

Compressor clutch is powered through the 10-amp A/C fuse and the compressor clutch relay, which is PCM-controlled.

When all inputs to PCM and ACP are within calibrated values, ACP signals the PCM to ground the compressor clutch and allow compressor clutch to engage. Compressor clutch is able to engage if climate control is set to any mode except OFF or ECON, outside temperature is greater than 50°F (10°C) in normal humidity conditions or 40°F (4°C) in high humidity conditions and compressor disabling codes have not been set.

If the windshield wipers have been on, the ACP will select the humidity condition for compressor operation. If the rear defogger, front defroster or defogger is selected, the ACP will select humid ambient temperature condition for compressor operation.

Once the A/C clutch is engaged, minimum compressor clutch on time is determined by either of 2 modes.

Extended Compressor At Idle

When vehicle speed drops to less than 18 MPH, minimum clutch on time is increased to about 45 seconds, providing a smoother idle at low vehicle speeds with A/C operating.

Minimum Compressor On Time

When vehicle is operating at speeds greater than 20 MPH, minimum on time is limited to 2-6 seconds before the ACP will allow compressor clutch disengagement.

After minimum on time has expired, ACP will request PCM to disengage compressor clutch only if low-side temperature is less than 30°F (-1°C). When low-side temperature reaches 45-50°F (7-10°C), ACP cycles the compressor on again.

This cycle continues until PCM disengages the clutch due to one of the following conditions: A/C low-pressure switch open, A/C low-side temperature less than 20°F (-7°C), A/C high-side temperature greater than 200°F (93°C), coolant temperature greater than 259°F (126°C), open or shorted A/C low-side sensor circuit or wide open throttle signal from PCM.

Except for wide open throttle signal, all of the above conditions will keep the compressor off as long as condition exists. Under the wide open throttle signal condition, PCM will disengage the compressor clutch for a maximum of 20 seconds.

On initial crank, ACP will check for indications of liquid refrigerant which may have collected at the compressor. If indications are found, the ACP will request compressor clutch engagement. After engine is started or shortly thereafter, the clutch will disengage and wait until normal calibrations and parameters are met to signal re-engagement of the clutch.

IDLE SPEED CONTROL

In order to minimize the effects of compressor operation on vehicle idle, the PCM can modify engine idle under A/C operation. When the PCM receives the clutch engagement signal from the ACP, the PCM adjusts the idle speed control motor in anticipation of increased engine load.

LOW REFRIGERANT MESSAGE

ACP also monitors inputs which would indicate low refrigerant charge. If the system charge falls below one-half of its capacity, ACP will display LOW A/C REFRIGERANT - SERVICE SOON message to warn the operator. The ACP will also store a trouble code in memory. Compressor clutch is shut off until low refrigerant condition or trouble code is cleared.

If system charge level drops to approximately one-fourth of system capacity, a message of VERY LOW A/C REFRIGERANT - COMPRESSOR OFF will be displayed and the ACP will store another trouble code.

Link Rod Adjustment

1. Remove right sound insulator and glove box. Start vehicle, and set ECC control panel to maximum heating. If outside temperature is greater than 90°F (33°C), disconnect in-car temperature sensor.
2. Allow 1-2 minutes for programmer arm to reach full heating position. Pull link rod from retainer on programmer output arm. Check air-mix valve for free travel.
3. Place air-mix valve in maximum heat position, and snap link rod into programmer output crank retainer. Programmer should be in maximum heat position. Cycle ECC control panel setting from maximum heating to maximum cooling and observe link rod for smooth operation. (Scheme 4)

Scheme 4

TROUBLE SHOOTING

Note. All A/C system diagnostics should begin with ECC SYSTEM CHECK.

AIR BAG WARNING

COOLING FANS

Cooling fan information is not available.

ECC SYSTEM CHECK

1. Correct any obvious faults such as low coolant level, coolant leaks, faulty aspirator hose, refrigerant leaks and vacuum leaks. Check if system operates as described in AIR DELIVERY MODE CONTROL under OPERATION. (Scheme 2) If system does not operate as described, go to next step.
2. Turn ignition on with engine off. Enter self-diagnostics, and check for trouble codes. See ACP SELF-DIAGNOSTICS under TESTING. If any trouble codes are present, repair cause of codes, and clear codes. See SERVICE MODE OPERATION & EXITING DIAGNOSTICS under TESTING. See charts in AUTOMATIC A/C-HEATER SYSTEMS - TROUBLE SHOOTING article in the AIR CONDITIONING & HEAT Section.
3. If trouble codes are not present, exit self-diagnostics. See SERVICE MODE OPERATION & EXITING DIAGNOSTICS under TESTING. Start engine, and bring it to normal operating temperature. Outside temperature must be more than 50°F (10°C). Set temperature at 60°F (16°C) and blower to HI speed on Climate Control Center (CCC).
4. If compressor and/or blower do not operate or interior temperature is not as selected, use ECC trouble shooting charts to diagnose problem by symptom. See ECC TROUBLE SHOOTING CHART SYMPTOM REFERENCE table. See charts in AUTOMATIC A/C-HEATER SYSTEMS - TROUBLE SHOOTING article in the AIR CONDITIONING & HEAT Section.

ECC TROUBLE SHOOTING CHART SYMPTOM REFERENCE

ACP SELF-DIAGNOSTICS

Note. Operating vehicle in SERVICE MODE for extended time periods without engine running will drain battery, possibly causing system to give false diagnostic information. If vehicle is to be operated in SERVICE MODE for more than 30 minutes, connect charger to battery.

Entering SERVICE MODE

1. To enter SERVICE MODE and self-diagnostics, turn ignition on with engine off. Simultaneously touch OFF and WARM buttons on Climate Control Center (CCC). (Scheme 1)
2. Hold buttons until a segment check is displayed on Instrument Panel Cluster (IPC). This should take about 3 seconds. If any segments of IPC do not glow, replace display.

Note. In SERVICE MODE, PCM, ACP, IPC and Supplemental Inflatable Restraint (SIR) system can be tested. Only information relating to A/C diagnostics is given in this manual.

ACP TROUBLE CODES

After SERVICE MODE is entered, all present trouble codes will be displayed. Each trouble code consists of system abbreviation, a 3-digit code identifier and letter "C" or "H".

System abbreviations are "E" for PCM codes, "I" for IPC codes, "A" for ACP codes and "R" for SIR codes. See ACP TROUBLE CODES table. A "C" or "H" at end of code indicates whether code is current (fault still exists) or code is historical (failure was present during one of last 50 key cycles).

ACP TROUBLE CODES

If codes do not exist in memory for ACP, a NO A CODES message will be displayed. If IPC cannot communicate with ACP, a NO A DATA message will be displayed.

To repair affected circuit, use trouble code charts. See A/C-HEATER SYSTEM TROUBLE SHOOTING - AUTOMATIC article in the AIR CONDITIONING & HEAT Section. After all trouble codes have been displayed, ACP system may be selected for testing. See SERVICE MODE OPERATION & EXITING DIAGNOSTICS under TESTING.

Note. Trouble code charts are provided only for those circuits and sensors which directly affect A/C operation.

SERVICE MODE OPERATION & EXITING DIAGNOSTICS

After trouble codes have been displayed, SERVICE MODE can be used to exit diagnostics or individually perform several tests on different systems.

Select System

Following trouble code display, first available system will be displayed (i.e., PCM). When selecting a test, 4 choices are available

1. Pressing OFF button on CCC will stop system selection process and return display to beginning of trouble code sequence.
2. Pressing blower fan down arrow (LO) button on CCC will display next available system selection. (Scheme 5) This allows display to list each system selection. PCM?, ACP?, SIR? and IPC? are 4 available system displays.
3. Pressing blower fan up arrow (HI) button on CCC will select displayed system for testing. (Scheme 5)
4. Pressing AUTO button on CCC will exit SERVICE MODE and diagnostics and return display to normal operation.

Note. System returns to mode it was in before it entered SERVICE MODE.

Scheme 5

Select Test Type

Having selected a system, first available test type will be displayed (i.e., PCM DATA). When selecting a specific test type, 3 actions are available

1. Pressing OFF button on CCC will stop test type selection process and return to next available system selection.
2. Pressing blower fan down arrow (LO) button on CCC will display next available test type for selected system. (Scheme 5) This allows all available test types to be displayed for selection. Test types can be repeated following display of last test type.
3. Pressing blower fan up arrow (HI) button on CCC will select displayed test type. (Scheme 5) Display will either indicate selected test type is in progress or first of several tests will appear.
4. Pressing AUTO or DEFOG button on CCC will stop diagnostics and return display to normal operation.

Select Test

1. Selection of DATA, INPUTS, OUTPUTS or OVERRIDES test type will result in first available test being displayed.
2. Last 4 characters of display will contain a test code to identify selection. First 2 characters are letters which identify system and test type; last 2 numbers identify test. (Scheme 5) When selecting a specific test, 4 options are available. Pressing OFF button on CCC will stop test selection process and return display to next available test type for selected system. Pressing blower fan down arrow (LO) button on CCC will display next smaller test number for selected test type. If button is pressed with lowest test number on display, highest test number will appear. Pressing blower fan up arrow (HI) button on CCC will display next larger test number for selected test type. If button is pressed with highest test number on display, lowest test number will appear. Pressing AUTO or DEFOG button on CCC will stop diagnostics and return display to normal operation.

Selecting CLEAR CODES

Selecting CLEAR CODES test will result in message CODES CLEAR being displayed along with selected system name. Message will appear for 3 seconds, indicating all codes for system have been cleared. After 3 seconds, system will return to next available test type. (Scheme 5)

ACP Snapshot Test

1. Selecting snapshot test type while in ACP system level, allows up to 3 snapshots, recorded at time of setting ACP trouble codes, to be recalled. A snapshot can also be recorded upon demand.
2. Selecting snapshot (pressing blower fan up arrow (HI) button) while in ACP system results in display of X### SNAPSHOT; ### is 3-digit trouble code. (Scheme 5) When selecting snapshot test type, several options are available: Pressing blower fan down arrow (LO) button allows scrolling through of ACP trouble codes list for snapshots stored in memory. (Scheme 5) After last ACP code (or third, if more than 3 codes are set), pressing LO button results in display of TAKE SNAPSHOT? message. Pressing LO button again will return to first X### SNAPSHOT? display. Pressing blower fan up arrow (HI) button at X### SNAPSHOT display changes display to X### DATA or SNAP DATA message to select snapshot data values. See ACP DATA DISPLAY CODES under TESTING. (Scheme 5) Press HI button to select a data test or press LO button to go to X### INPUTS or SNAP INPUTS selection. Pressing HI button here selects input test. Pressing LO button here will display X### DATA or SNAP DATA screen again. (Scheme 5) At each data or input test, display is controlled as it would be for non-snapshot data and input displays; however, all values and status information represent memorized vehicle conditions. Pressing HI button with TAKE SNAPSHOT displayed will display SNAPSHOT TAKEN message to indicate new information has been stored in memory. (Scheme 5) After a few seconds, display will change to X### DATA or SNAP DATA screen. Pressing OFF with X### SNAPSHOT displayed will return display to next available test selection. (Scheme 5)

Exiting SERVICE MODE

To exit SERVICE MODE, press AUTO or DEFOG button on CCC or turn ignition off. Trouble codes are not erased (cleared) when this is done.

ACP DATA DISPLAY CODES

Note. For complete information on all PCM and IPC trouble codes, see appropriate article in the ENGINE PERFORMANCE Section.

ACP Data Displays & Status Lights

1. While in ACP system level in SERVICE MODE, indicators on climate control panel display status of certain modes. Different modes of operation are shown by status light turning on or off. Status lights are as follows: AUTO indicator is turned on whenever ACP is commanding recirculation solenoid to be engaged. Light does not indicate valve has responded to ACP command; it only indicates ACP has signaled valve to move. Front defroster status indicator is turned on when ACP requests PCM to engage A/C compressor clutch. Light does not indicate clutch has responded to ACP command; it only indicates ACP has signaled clutch to engage. Rear defogger status indicator light is turned on whenever ACP senses low refrigerant pressure switch is open. Light should remain off if system is fully charged and correctly controlled. Light comes on when outside temperature drops to about -5°F due to pressure-temperature relationship of R-12. LO status indicator is turned on when ACP signals defrost solenoid to be engaged. Light does not indicate valve has responded to ACP command; it only indicates ACP has signaled valve to move. HI status indicator is turned on when ACP signals air-up solenoid to be engaged. Light does not indicate valve has responded to ACP command; it only indicates ACP has signaled valve to move. DEFOG status indicator is turned on when ACP signals air-down solenoid to be engaged. Light does not indicate valve has responded to ACP command; it only indicates ACP has signaled valve to move.
2. During trouble shooting, data displays can be used to compare a vehicle with problems to a properly functioning vehicle. Following are brief summaries of parameters.

Code AD20

Commanded blower voltage reading is displayed in modulated pulse width from zero to 100 percent.

Code AD21

Coolant temperature sent from PCM to ACP is displayed in degrees Celsius (from -40° to 151°C).

Code AD22

Commanded air-mix valve position is displayed as percentage. A value close to 100 percent represents a cold air-mix and a value close to zero percent represents a warm air-mix.

Code AD23

Actual air-mix valve position is displayed as percentage. This value should follow commanded air-mix valve position (BD22), except if valve is commanded beyond its mechanical limits.

Code AD24

Air delivery mode is displayed as a number, ranging from zero to 10. Each number represents an air delivery mode. See AIR DELIVERY MODES table.

AIR DELIVERY MODES

Code AD25

In-car temperature is displayed in degrees Celsius (from -40°C to 102°C).

Code AD26

Actual outside temperature is displayed in degrees Celsius (from -40°C to 53°C). This value represents actual sensor temperature without any alterations.

Code AD27

High-side temperature is displayed in degrees Celsius (from -38°C to 185°C). High-side temperature sensor is mounted in liquid R-12 line between condenser and orifice tube.

Code AD28

Low-side temperature is displayed in degrees Celsius (from -40°C to 102°C). Low-side temperature sensor is mounted in liquid R-12 line between evaporator and orifice tube.

Code AD32

Sunload temperature sensor is displayed as percentage from zero (bright) to 100 (darkness). Sunload temperature sensor is mounted under defogger grille, center position, at base of windshield.

Code AD70

This displays rear blower feedback in voltage. In early production vehicles (AD99 = 1847), value displayed is equal to ignition voltage minus voltage at rear blower (zero volts at maximum blower and ignition voltage when rear blower is off). In later production models, value displayed is voltage at rear blower (zero volts when rear blower is off and ignition voltage when rear blower is at maximum).

Code AD71

Integral control term is displayed in counts. Integral control term is used to compensate for inside air temperature sensor leading/lagging actual temperature.

Code AD98

Ignition cycle value is number of times ignition has been cycled off since an ACP trouble code was last detected. After 50 ignition cycles without any malfunction, all ACP codes are cleared.

Code AD99

ACP SOFTWARE ID (PROM identification) is displayed as a number of up to 4 digits. This can be used to determine if proper PROM was installed in ACP.

ACP INPUT TESTS

1. To access input tests, see SERVICE MODE OPERATION & EXITING DIAGNOSTICS under TESTING. (Scheme 5) During trouble shooting, input test feature allows technician to see state of a selected device.
2. Input tests will display state of selected device as HI or LO. Display also indicates if input changed state so technician can activate or deactivate any listed device and return to display to see if it changed state.
3. If a change of state occurred, an X will appear next to HI/LO indicator; otherwise, a zero will remain displayed. An X will only appear once per selected input, although HI/LO indication will continue to change as input changes. Some tests are very brief; an X display indicates change in test mode. Following are brief summaries of input test parameters.

AI01

When A/C system is low on refrigerant, display will read LO.

AI02

When wiper switch is in any ON position, display will read

HI.

ACP OVERRIDE DISPLAYS

1. To access override displays, see SERVICE MODE OPERATION & EXITING DIAGNOSTICS under TESTING. (Scheme 5) During trouble shooting, override feature allows testing of certain system functions regardless of normal instructions.
2. Selected system function will be represented as a percentage of its full range. Value will be displayed on climate control panel. Display will alternately feature "--" for 1 second followed by normal program value for 5 seconds. Alternating display indicates function is not currently being overridden.
3. After an override has been selected, value may be changed by pressing WARM or COOL button on CCC (display will no longer alternate to "--" display). Touching WARM button increases value; touching COOL button decreases value.
4. When button is released, display may remain at override value or automatically return to normal program control, depending on override function. If display remains at override value, normal control can be resumed in any of 3 ways. Selecting another override test cancels current override. Selecting another system cancels current override. Overriding value beyond either extreme (zero or 99) will cause a momentary display of "--" and value will jump to opposite extreme. If button is released while "--" is displayed, normal program control resumes and display will alternate again.
5. When override is selected, other tests within selected system may be activated at same time. After selecting an override test, touching OFF button allows selection of another test type. CCC will continue to display selected override.
6. By selecting and testing another test type while WARM or COOL button is touched, monitoring override effect on different vehicle parameters is possible. ACP override display codes are as follows

AS00

NONE is displayed as overrides are not active at this point.

AS01

Program number override can be controlled between zero (maximum A/C) and 99 (maximum heat). Display will hold override value when buttons are released.

AS12

Air-mix door position can be overridden from zero to 99. Display will hold override value when buttons are released.

AS13

Air delivery mode can be overridden from zero to 10 to vary air delivery mode. See AIR DELIVERY MODES table in ACP DATA DISPLAY CODES under TESTING.

AS16

Blower speed can be overridden from zero percent to 100 percent.

AS19

Overrides outside temperature reading. Outside temperature update override can be used to immediately update displayed outside temperature reading to actual outside temperature reading. This is done through by-passing filter used to avoid incorrect swings in outside temperature sensor reading.

AS20

Override solenoid cycling between on and off. On early production vehicles (AD99 = 1847), all actuators will be applied while WARM button is pressed and all actuators will be off while COOL button is pressed. (Scheme 1) On later production vehicles, actuators will individually cycle on for 5 seconds. Lights on CCC will indicate which actuator is currently cycling. See SOLENOID CYCLING STATUS LIGHT IDENTIFICATION table. Actuator can be held in on (cycling) mode by pressing COOL button when they are cycling (display will read 00). Press WARM button to resume cycling (display will read 99).

SOLENOID CYCLING STATUS LIGHT IDENTIFICATION

Removal & Installation

1. Disconnect negative battery cable. Remove right sound shield. Remove glove box. Remove PCM bracket screws. Position PCM aside to access programmer mounting screws.
2. Disconnect link rod from programmer. Remove programmer electrical and vacuum connectors. Remove 3 programmer attaching screws and programmer. (Scheme 4) To install, reverse removal procedure. Adjust air-mix valve. See «AIR-MIX VALVE ADJUSTMENT»(/cadillac/seville/iv-1992-1997/remont/automatic-hvac-system/#ac-heater-system-automatic).

Discharge A/C system using approved refrigerant recovery/recycling equipment. Remove air cleaner element. Disconnect accumulator inlet and outlet refrigerant lines. Plug all lines and openings. Remove bolts retaining accumulator. Remove accumulator. To install, reverse removal procedure. Tighten bolts and fittings to specification. See TORQUE SPECIFICATIONS . Evacuate and recharge A/C system.

Disconnect negative battery cable. Remove instrument panel top cover. Disconnect aspirator hose and electrical connector. Remove in-car temperature sensor retaining screw. Remove sensor. To install, reverse removal procedure.

1. Disconnect negative battery cable. Remove cross-tower brace. Remove cowl relay center bracket, and position aside. Remove wiring harness bracket from blower motor. Disconnect wiring and cooling hose from blower motor.
2. Remove 6 blower motor mounting screws. Remove MAP sensor bracket, and set aside. Tilt blower motor in case and detach fan. Remove blower motor and fan from case. To install, reverse removal procedure.

1. Disconnect negative battery cable. Discharge A/C system using approved refrigerant recovery/recycling equipment. Remove serpentine drive belt. Raise and support vehicle. Remove A/C compressor and engine splash shields and retainer. Unplug electrical connections from compressor.
2. Remove compressor hose retainer bolt. Remove compressor from mounting bracket. To install, reverse removal procedure. Evacuate and recharge A/C system.

1. Disconnect negative battery cable. Discharge A/C system using approved refrigerant recovery/recycling equipment. Remove engine torque strut. Remove rear cooling fan. Remove radiator top support bracket. Disconnect high-side pressure fittings to and from condenser. Cap all openings.
2. Remove condenser support screws, brackets and insulators. Remove condenser. To install, reverse removal procedure. Tighten fittings to specification. See «TORQUE SPECIFICATIONS»(/cadillac/seville/iv-1992-1997/remont/automatic-hvac-system/#ac-heater-system-automatic) . Evacuate and recharge A/C system.

Removal (4.6L)

1. Disconnect negative battery cable. Discharge A/C system using approved refrigerant recovery/recycling equipment. Remove right sound insulator. Disconnect electrical connectors from power module and blower motor and powertrain control module.
2. Remove bolt securing evaporator core housing to front of dashboard. Bolt is located above carpet, directly behind left side of console. Remove 2 bolts securing wiring harness pass-through to front of dashboard.
3. Remove cross car brace. Disconnect electrical connectors from ignition control module, blower motor, rear heated oxygen sensor,A/C high and low side temperature sensors, 2 connectors at Heating Ventilation and Air Conditioning (HVAC) module, and one connector at A/C low pressure switch.
4. Remove ignition control module, air cleaner and evaporator/accumulator line. Install engine support. Raise and support vehicle. Remove left front wheel. Remove intermediate shaft pinch bolt from rack and pinion gear.
5. Remove exhaust pipe at catalytic converter and 2 lower heat shield bolts. Disconnect electrical connectors at power steering pressure switch, vehicle speed sensor and knock sensor. Remove 4 bolts securing frame to body. Lower vehicle and powertrain. Raise vehicle.
6. Remove 2 upper exhaust heat shield bolts and 4 lower evaporator and blower assembly. Cut lower portion of rubber evaporator and blower assembly at guides. Lower vehicle.
7. Remove 2 ground wires attached to engine head. Remove electrical harness from camshaft cover. Move all loose electrical harnesses to left side of vehicle. Cut upper portion of rubber evaporator and blower assembly insulator. Remove power module and blower motor. Remove 4 evaporator inlet bracket-to-evaporator and blower assembly bolts.
8. Remove bolt securing liquid line to bracket above blower motor. Remove evaporator core from liquid line. Remove 4 upper evaporator and blower assembly bolts. Remove rubber insulator covering evaporator core housing. Remove 3 bolts securing evaporator core housing to front of dashboard. Reposition engine as necessary and remove evaporator core housing. Remove evaporator core.

Installation

To install, reverse removal procedure. Tighten fittings to specification. See TORQUE SPECIFICATIONS .

Removal (4.9L)

1. Disconnect negative battery cable. Discharge A/C system using approved refrigerant recovery/recycling equipment. Drain radiator. Remove cross-tower support bracket and cowl relay center bracket. Disconnect electrical connectors from power module, blower motor and blower motor resistor.
2. Disconnect heater hose lines at core. Remove evaporator line retaining bracket. Disconnect core refrigerant lines, and plug all openings. Remove heater hose "T" connector. Remove 2 heat shield screws in engine compartment. Raise and support vehicle. Remove screws and heat shield.
3. Remove A/C module retaining screws. Lower vehicle. Remove MAP sensor bracket. Remove diverter valve and 2 harness hold-down brackets from valve cover. Remove sound insulator retaining clips. Remove power module, blower motor and sound insulator.
4. Remove A/C module cover screws. Remove module cover, sound insulator and seal. Remove clamp retaining evaporator, and remove evaporator core from case.

To install, reverse removal procedure. Tighten fittings to specification. See TORQUE SPECIFICATIONS . Evacuate and recharge A/C system.

1. Disconnect negative battery cable. Partially drain coolant. Remove glove box unit and right lower sound insulator. Disconnect electrical connectors and remove power module. See POWER MODULE.
2. Remove heater core cover. Remove inlet and outlet hoses from heater core. Remove 2 heater core retaining screws. Remove heater core. To install, reverse removal procedure. Perform air-mix valve adjustment. See «AIR-MIX VALVE ADJUSTMENT»(/cadillac/seville/iv-1992-1997/remont/automatic-hvac-system/#ac-heater-system-automatic) .

LOW PRESSURE SWITCH

Note. Low pressure switch is mounted on a Schrader valve so system does not need to be discharged.

Disconnect negative battery cable. Disconnect low pressure switch electrical connector. Unscrew switch from refrigerant line. To install, reverse removal procedure.

Disconnect negative battery cable. Remove radiator core plastic cover. Unplug outside temperature sensor electrical connector. Remove sensor. To install, reverse removal procedure.

Disconnect negative battery cable. Remove cowl cross-tower brace. Disconnect electrical connectors, retainers and mounting screws from power module. Remove power module from evaporator case. To install, reverse removal procedure.

Disconnect negative battery cable. Remove windshield center defogger grille. Remove sunload sensor screws and connector. Remove sunload sensor. To install, reverse removal procedure.

Turn front wheels to right. Raise and support vehicle. Remove mounting screws and vacuum hose from tank. Remove vacuum tank. To install, reverse removal procedure.

TORQUE SPECIFICATIONS

TORQUE SPECIFICATIONS

Scheme 6

Automatic A/C-Heater System Wiring Diagram (1 Of 2). Scheme 7

Automatic A/C-Heater System Wiring Diagram (2 Of 2). Scheme 8

See also:
• A/C-HEATER SYSTEM TROUBLE SHOOTING - AUTOMATIC
• AIR-MIX VALVE ADJUSTMENT