A/c-Heater System - Automatic Chevrolet Corvette C4

A/C SYSTEM SPECIFICATIONS

A/C SYSTEM SPECIFICATIONS

DESCRIPTION

Electronic Climate Control (ECC) system uses an electrically-operated, rheostat-controlled motor to position temperature door actuator. The ECC system electrically activates AUTO, BI-LEV, ECON, HTR, and defrost modes through use of vacuum solenoids in A/C-heater programmer.

ECC system components include: A/C-heater control panel, blower control module, in-car temperature sensor, outside (ambient) temperature sensor, air distribution assembly (containing airflow control valves), evaporator, and heater core.

Combined with Cycling Clutch Orifice Tube (CCOT) system, A/C-heater control panel regulates blower fan motor speed and generates command signals to A/C-heater programmer and blower control module. The CCOT refrigeration system is the same as General Motors vehicles with manual A/C-heater systems.

A/C-HEATER CONTROL PANEL

The A/C-heater control panel consists of electronic circuit boards housed in a plastic box, attached to instrument panel. Pressure sensitive, low current buttons on A/C-heater control panel are used to control operation of automatic A/C-heater system. A Light Emitting Diode (LED) indicator goes on when an operating mode button is pressed. By pressing specific buttons, driver selects desired operating mode or temperature setting. (Scheme 1)

OFF Mode

In OFF mode, fan motor and A/C compressor will not run. Air will flow through vents when car is moving.

Scheme 1

AUTO Mode

In AUTO mode, temperature is controlled automatically by ECC system. The ECC System will adjust to temperature range selected by driver. Fan motor will vary its speed automatically unless it is changed by pressing down or up arrow buttons.

Recirculate Mode

In recirculate mode, maximum cooling is provided by recirculating passenger compartment air and distributing it through instrument panel outlets. If outside temperature sensor detects ambient temperature of less than 40°F (4°C), Light Emitting Diode (LED) will light above recirculation button. LED will light for approximately 1 second and system will then switch to AUTO mode and corresponding LED will light. Recirculation mode will not operate under 40°F (4°C).

Bi-Level Mode

When in bi-level mode, system will let air into vehicle only through bi-level, heater and A/C outlets. Fan motor speed is controlled by input signals from Central Control Module (CCM) and individual sensors. It also operates to defog side windows. Fan motor can be adjusted by pressing down or up arrow buttons.

Vent Mode

In vent mode, compressor will not run. System will adjust to temperature selected by driver, but cannot cool inside vehicle temperature cooler than outside temperature. Fan motor speed is automatically controlled, unless fan speed is changed by pressing down or up arrow button.

Heater Mode

In heater mode, most air entering vehicle is forced to floor with a small amount directed to defroster outlets. Fan motor speed is automatically controlled, unless fan speed is changed by pressing down or up arrow button. In-car temperature setting will adjust to temperature setting selected by driver, unless setting is below outside temperature.

Defogger Mode

To enter defogger mode, defrost and heater buttons must be depressed simultaneously. Upon entry, both Light Emitting Diode (LED) lights will illuminate and air will flow between defroster and floor outlets.

Defroster Mode

In defroster mode, all air is forced to windshield. Fan motor speed will run at a fixed high speed with no delay. After start-up, high fan motor speed can be readjusted by pressing down arrow or AUTO button. With ignition on, a small amount off airflow is directed to the floor. This purges heated core and prevents the windshield from fogging. Purge duration lasts for 15 seconds.

Rear Defogger/Defroster Mode

When in this mode, driver may defrost or defog rear window and activate heated mirrors (if equipped). Rear defogger/defroster mode will not operate unless ignition is on and engine is running.

Fan Speed

When fan AUTO button is pressed, fan speed is controlled automatically by ECC system. To override automatic fan speed control, press fan up or down button. Upon pressing either button, Liquid Crystal Display (LCD) on A/C-heater control panel will show blower symbol and current fan speed. There are 10 fan speed numbers representing fan speed range.

Outside Heated Mirrors Mode

This mode will operate heated mirrors (convertible models). First time button is pressed, system will run for approximately 10 minutes, then shut off. After completing this cycle, system will run for approximately 5 minutes when reactivated. The outside heated mirrors will only operate with the ignition on and the engine

A/C-HEATER PROGRAMMER

The A/C-heater programmer is located behind left side of instrument panel, right of steering column. Air valves in A/C system are operated by electrical solenoids in A/C-heater programmer and actuators, located near air valves. Solenoids are commanded ON or OFF depending on mode selected by driver. When a mode is selected, signal is sent to A/C-heater programmer. A/C-heater programmer then energizes solenoids, allowing vacuum to vacuum actuators to move air valves.

AIR MIX DOOR ACTUATOR

Air mix door actuator is electrically controlled. Valve is in cool position when cold temperature is selected, preventing air from blowing through heater core. When temperature other than cold is selected, air mix door partially or fully opens, allowing some or all of the air to flow through heater core.

FRONT & REAR MODE VALVES

Front and rear mode valves determine whether air flows to heater outlets, A/C-defrost outlets, or both. Position of valves is determined by mode selected by driver. In AUTO mode, the A/C-heater programmer determines position of the mode valves depending upon existing heating and cooling requirements.

IN-CAR TEMPERATURE SENSOR

In-car temperature sensor is located in air conditioning outlet, front of passenger seat. It senses temperature of air inside vehicle. Sensor generates a low current signal corresponding with actual in-car temperature. Signal is fed to A/C-heater control panel, which controls blower speed and temperature door position to obtain desired temperature.

OUTSIDE TEMPERATURE SENSOR

Outside temperature sensor is located on right side of radiator upper support. It senses temperature of outside air temperature. Sensor generates a low current signal, directly proportional to actual outside temperature.

RECIRCULATION VALVE

Recirculation valve is open in most operating modes permitting outside air to enter plenum. Valve is closed in recirculation mode and at temperature setting of 60°F (15°C). When closed, air from inside vehicle is recirculated for maximum cooling.

SETTING TEMPERATURE

To set temperature, press TEMP SET up or down button until desired temperature is displayed on A/C-heater control panel. Down arrow will lower temperature to 65°F (18°C). If down arrow is pressed again, set temperature will lower to 60°F (15°C) and maximum cooling is provided. Up arrow will raise temperature to 85°F (29°C). If up arrow is pressed again, set temperature will increase to 90°F (32°C) and maximum heating is provided.

SUN LOAD SENSOR

Sun load sensor is located under windshield, mounted on instrument panel grille. Sensor measures amount of heat generated from sun shining on vehicle.

AIR BAG WARNING

Disabling System

1. Turn ignition off. Disconnect and isolate negative battery cable. Remove SIR fuse or air bag fuse from main fuse block. Main fuse block is located behind passenger's side of instrument panel.
2. Remove left sound insulator, located under steering column. Remove Connector Position Assurance (CPA) clip from Yellow 2-pin SIR connector at base of steering column. Disconnect Yellow 2-pin SIR harness connector.

System Functional Check

1. Ensure ignition is off. Connect Yellow 2-pin SIR connector at base of steering column. Install Connector Position Assurance (CPA) into Yellow 2-pin SIR connector.
2. Install SIR or air bag fuse in main fuse block. Install left sound insulator. Turn ignition switch on.
3. Ensure INFL REST (inflatable restraint) light on driver information center flashes 7-9 times and then goes out. Driver information center is located above A/C-heater control panel. If light does not operate as described, SIR system is malfunctioning and needs repair.

A/C-HEATER FUNCTIONAL TEST

1. Close doors and windows.
2. Temperature indications at condenser inlet and upper right outlet.
3. Close left, center, and lower right outlets.
4. Start and run engine at 2000 RPM.
5. Set temperature to 60°F with COOL button.
6. After one minute, the air temperature drop at the upper right outlet should be as specified in the A/C HEATER RESPONSE TEMPERATURE.

A/C-HEATER SYSTEM RESPONSE TEMPERATURE

Note. Only a small quantity of air will be discharged at the S.W.D outlets. (Scheme 2)

Note. A - Noticeable blower speed increase must occur when switching from MANUAL to AUTO. B - Listen for reduction of air noise due to recirculation door closing. C - Check for small amount of airflow at S.W.D. outlets.

Scheme 2

SELF-DIAGNOSTICS

Note. Manufacturer recommends that a Tech 1 tester be used in testing of A/C-heater system circuits.

If a system fault is detected, Light Emitting Diode (LED) of mode system will flash at a rate of 60 times a minute. Fault code(s) will then be stored.

To enter self-diagnostics, press and hold fan up and down arrow at same time for approximately 5 seconds. Liquid Crystal Display (LCD) will show -00. Press AUTO FAN and LCD will show fault codes stored in system.

When in diagnostic mode, it is possible to check several different system parameters (circuits or systems). This is done by pressing either fan up or down arrow button. Once parameter to be checked is chosen, press fan AUTO button and a diagnostic value will be displayed on LCD. Refer to ELECTRONIC CLIMATE CONTROL PARAMETERS. (Scheme 3)

Scheme 3

TROUBLE CODES

Note. For diagnosis of ECC system trouble codes, refer to AUTO A/C-HEAT DIAGNOSIS article in this section.

TROUBLE CODES

TESTING

Note. Manufacturer recommends that a Tech 1 tester be used in testing of A/C-heater system circuits.

1. Disconnect negative battery cable. Remove instrument panel trim plate and upper trim pad assembly.
2. Remove screws securing A/C-heater control panel. Remove A/C-heater control panel by tipping control panel face forward and disconnecting electrical connector. To install, reverse removal procedure.

ACCUMULATOR

1. Disconnect negative battery cable. Discharge A/C system using approved refrigerant recovery/recycling equipment. Remove air intake duct. Remove accumulator and compressor hose from accumulator.
2. Loosen accumulator bracket clamp bolt and remove accumulator from bracket. Drain oil from accumulator and measure quantity. To install, reverse removal procedure.
3. Tighten accumulator bracket clamp bolt to 44 INCH lbs. (6 N.m). Refill accumulator with quantity of oil equal to that measured during disassembly plus 2 ounces. Evacuate and recharge system. Check for leaks.

BLOWER MOTOR

1. Disconnect negative battery cable. Remove front wheelwell rear panel and set wheelwell aside. Remove blower motor cooling tube. Remove relay.
2. Remove screws and blower motor. Remove impeller from blower motor shaft. To install, reverse removal procedure.

CONDENSER

1. Disconnect negative battery cable. Drain radiator. Discharge A/C system using approved refrigerant recovery/recycling equipment. Remove upper fan shroud. Disconnect compressor and evaporator hose fitting at condenser. Remove condenser.
2. To install, reverse removal procedure. Install new "O" rings on fittings. Evacuate and recharge A/C system. Tighten evaporator hose to condenser fitting to 12 ft. lbs. (16 N.m). Tighten compressor hose to condenser fitting to 30 ft. lbs. (40 N.m).

EVAPORATOR CORE

1. Disconnect negative battery cable. Drain cooling system. Discharge A/C system using approved refrigerant recovery/recycling equipment. Remove front wheelwell rear panel and seal.
2. Remove blower motor resistor electrical connector. Remove evaporator outlet hose. Disconnect pressure cycling switch electrical connector. Remove pressure cycling switch.
3. Disconnect heater hoses. Remove heater hose bracket at inner fender. Disconnect inlet hose at evaporator and remove hose bracket at inner fender. Remove nuts and bolts retaining evaporator assembly to firewall.
4. Split evaporator case halves and remove evaporator core. To install, reverse removal procedure. Clean cover mating surfaces. Install cover with new evaporator on bulkhead studs. Fill cooling system. Evacuate and recharge A/C system. Check for leaks.

Scheme 4

HEATER CORE

1. Remove instrument panel upper trim pad. Drain cooling system. Remove in-car temperature sensor aspirator hose and electrical connector.
2. Remove floor heat deflector screws. Remove right knee bolster brace. Remove floor heat deflector. Remove relays from relay bracket. Loosen nuts retaining wiring harness retainer to radio receiver.
3. Slide wiring harness retainer from radio receiver. Remove harness from wiring harness retainer. Remove wiring harness retainer. Remove carrier nuts from right pillar.
4. Remove relay bracket. Remove passenger knee bolster brace attachments. Disconnect side window defroster duct clip and duct hose from knee bolster brace. Pull carrier back and remove passenger knee bolster brace.
5. Disconnect electrical connectors from radio receiver. Disconnect cruise control module electrical connector. Remove screws attaching side window defroster duct to rear of heater case.
6. Remove fuse block from carrier. Remove vacuum hose from actuator. Remove harness from retainer clip on bottom of rear heater case. Disconnect side window defroster center duct in heater case.
7. Remove rear heater case screws. Remove rear heater case half. Remove cooling system reservoir. Disconnect heater hoses from heater core. Remove heater core from case. To install, reverse removal procedure. Fill cooling system. Check for leaks.

Scheme 5

HEATER CORE CASE

1. Remove heater core. See HEATER CORE under REMOVAL & INSTALLATION. Remove evaporator core to gain access to front half of heater core case attachments on front of plenum.
2. See EVAPORATOR CORE under REMOVAL & INSTALLATION. Remove front half of heater core case. To install, reverse removal procedure.

1. Disconnect negative battery cable. Remove glove box. Remove bolts retaining in-car temperature sensor to instrument panel carrier.
2. Remove aspirator hose from sensor. Remove electrical connector. Remove in-car temperature sensor. To install, reverse removal procedure. Tighten sensor bolts to 12 INCH lbs. (1.4 N.m).

ORIFICE TUBE

1. Discharge A/C system using approved refrigerant recovery/recycling equipment. Disconnect evaporator inlet hose from evaporator. Remove orifice tube from evaporator inlet hose.
2. To install, reverse removal procedure. Evacuate and recharge A/C system. Check for leaks.

1. Disconnect negative battery cable. Disconnect outside temperature sensor connector. Remove bolt securing sensor to radiator upper support.
2. Remove sensor by pulling wire and grommet through grommet opening in radiator upper support. To install, reverse removal procedure. Tighten outside temperature sensor bolt to 17 INCH lbs. (1.9 N.m).

1. Disconnect negative battery cable. Remove instrument panel lower left trim panel. Remove A/C-heater programmer electrical connector. Remove air valve actuator vacuum harness assembly. (Scheme 6)
2. Remove A/C-heater programmer attaching screws. Remove A/C-heater programmer. To install, reverse removal procedure. Tighten the A/C-heater programmer screws to 17 INCH lbs. (1.9 N.m).

Scheme 6

1. Disconnect negative battery cable. Remove instrument grille from instrument panel.
2. Remove sun load sensor from instrument panel wiring harness. Remove sun load sensor from instrument panel grille. To install, reverse removal procedure.

AIR MIX DOOR MOTOR

1. Disconnect negative battery cable. Remove heater core case. See «HEATER CORE CASE»(/chevrolet/corvette/c4-1984-1998/remont/automatic-hvac-system/#ac-heater-system-automatic__heater-core-case) under REMOVAL & INSTALLATION.
2. Remove air mix door motor electrical connector and motor from heater core case. To install, reverse removal procedure.

Wiring Diagram. Scheme 7

See also:
• SERVICING PRECAUTIONS
• HEATER CORE CASE