Heater System GMC Suburban I

DESCRIPTION

System blends heated outside air with cooler outside air to obtain desired temperature. Major components of the system are a blower motor, air inlet assembly, heater air distributor assembly, and heater control panel.

AUXILIARY HEATER BLOWER SWITCH

A 3-speed blower switch (if equipped) is located on instrument panel, to right of steering column. When switch is in OFF position, auxiliary system does not operate.

BLOWER SPEED SWITCH

The blower speed knob selects low, medium, or high blower speed.

MODE SELECTOR

The mode selector directs discharge air to windshield, floor, or dash outputs, as desired by driver.

TEMPERATURE CONTROL SELECTOR

The temperature control lever or knob controls discharge air temperature in all mode positions. Full hot position provides maximum heat. Full cold position provides unheated air.

VENT Mode

Air is directed to instrument panel outlets.

BI-LEV Mode

Air is directed to instrument panel and floor outlets. A slight amount of air is directed to defroster and side window defogger outlets.

HEAT Mode

Air is diverted to floor outlets to heat passenger compartment. A slight amount of air is directed to windshield and side window defogger outlets. BLEND Mode

Air is divided between instrument panel and floor outlets, with a slight amount of air going to defroster outlets.

DEF Mode

Air is directed to windshield defroster outlets. A slight amount of air is diverted to floor outlets and side window defogger outlets.

ADJUSTMENTS

Note. Information on temperature control cable adjustment is not available.

TROUBLE SHOOTING

Note. Before performing trouble shooting procedures, ensure HTR/AC fuse is okay.

Note. For Trouble Shooting information not covered in this article, refer to the appropriate A/C-HEATER SYSTEM article in the AIR CONDITIONING & HEAT section.

A/C-HEATER SYSTEM - Suburban

A/C-HEATER SYSTEM - Except Suburban

BLOWER MOTOR INOPERATIVE

1. Turn ignition on. Connect test light between blower switch connector Brown wire and ground. If test light glows, go to next step. If test light does not glow, repair Brown wire between blower switch connector and fuse block.
2. Set blower switch to high speed position. Connect test light between blower switch connector Orange wire and ground. If test light glows, go to next step. If test light does not glow, replace blower switch.
3. Disconnect blower motor connector. Connect test light between blower motor connector Orange wire and ground. If test light glows, go to next step. If test light does not glow, repair open Orange wire between blower switch connector and blower motor connector.
4. Connect test light between blower motor connector Orange wire and Black wire. If test light glows, replace blower motor. If test light does not glow, repair Black wire from blower motor connector to ground.

BLOWER MOTOR OPERATES AT LOW &/OR MEDIUM SPEED ONLY

1. Turn ignition on. Set blower switch to high speed position. Connect test light between Orange wire at blower switch connector and ground. If test light glows, go to next step. If test light does not glow, replace blower switch.
2. Connect test light between Orange wire at blower resistor connector and ground. If test light glows, replace blower resistor. If test light does not glow, repair open Orange wire between blower resistor and blower switch.

BLOWER MOTOR OPERATES AT HIGH SPEED ONLY

1. Turn ignition on. Set blower switch to speed that does not operate. Connect test light between wire of inoperative speed position at blower switch connector and ground. Low speed is Yellow wire; medium low speed position is Tan wire; medium high speed position is Light Blue wire.
2. If test light does not glow, replace blower switch. If test light glows, connect test light between Yellow wire, Tan wire or Light Blue wire (depending on switch position) at blower resistor connector and ground.
3. If test light does not glow, repair open Yellow wire, Tan wire or Light Blue wire between blower resistor and blower switch. If test light glows, go to next step.
4. Connect test light between Orange wire at blower resistor and ground. If test light glows, wire circuit is okay. If test light does not glow, replace blower resistor.

AUXILIARY BLOWER MOTOR INOPERATIVE

1. Turn ignition on. Connect test light between Brown wire terminal of high blower relay connector and ground. High blower relay is located on auxiliary heater. If test light glows, go to next step. If test light does not glow, repair open Brown wire between high blower relay and fuse block.
2. Connect test light between Red wire terminal of high blower relay and ground. If test light glows, go to next step. If test light does not glow, repair open Red wire between high blower relay and fuse relay center under hood.
3. Check for continuity between Yellow wire at high blower relay connector and blower motor connector. If continuity exists, go to next step. If continuity does not exist, repair open Yellow wire between high blower relay connector and blower motor connector.
4. Check for continuity between Black wire at blower motor connector and ground. If continuity exists, go to next step. If continuity does not exist, repair open Black wire between blower motor connector and ground.
5. Check for continuity between Black wire at rear auxiliary heater control switch and ground. If continuity exists, go to next step. If continuity does not exist, repair open Black wire between rear auxiliary heater control switch connector and ground.
6. Set rear auxiliary heater control switch in high position. Check for continuity between Black wire and White wire at rear auxiliary heater control switch. If continuity exists, replace blower motor. If continuity does not exist, replace rear auxiliary heater control switch.

AUXILIARY BLOWER MOTOR OPERATES AT LOW &/OR MEDIUM SPEED ONLY

1. Turn ignition on. Set blower switch to high speed position. Connect test light between Brown wire at high blower relay (located on auxiliary heater) and ground. If test light glows, go to next step. If test light does not glow, repair open Brown wire between high blower relay and splice near relay leads.
2. Connect test light between White wire and Brown wire at high blower relay. If test light glows, go to next step. If test light does not glow, check for open White wire between high blower relay connector and rear auxiliary heater control connector. If wire is okay, replace rear auxiliary heater control switch.
3. Connect test light between Red wire at high blower relay and ground. If test light glows, go to next step. If test light does not glow, repair open Red wire between high blower relay and splice near relay leads.
4. Check for continuity of Yellow wire between high blower relay connector and blower motor connector. If continuity exists, replace high blower relay. If continuity does not exist, repair open in Yellow wire between high blower relay connector and blower motor relay.

AUXILIARY BLOWER MOTOR DOES NOT OPERATE IN MEDIUM SPEED

1. Turn ignition on. Set rear auxiliary heater control switch to medium speed position. Connect test light between Brown wire terminal at medium blower relay connector (located on auxiliary heater) and ground. If test light glows, go to next step. If test light does not glow, repair open Brown wire between medium blower relay and splice near relay leads.
2. Connect test light between Red wire (terminal C2) and Brown wire of medium blower relay connector. If test light glows, go to next step. If test light does not glow, check for open Red wire between medium blower relay connector and rear auxiliary heater control switch connector. If wire is okay, replace rear auxiliary heater control switch.
3. Connect test light between Red wire (terminal C1) at medium blower relay connector and ground. If test light glows, go to next step. If test light does not glow, repair open Red wire between medium blower relay and splice near relay leads.
4. Connect test light between Light Blue wire terminal of medium blower relay and ground. If test light glows, repair open Light Blue wire between medium blower relay connector and blower resistor connector. If test light does not glow, replace medium blower relay.

AUXILIARY BLOWER MOTOR DOES NOT OPERATE IN LOW SPEED

1. Turn ignition on. Set rear auxiliary heater control switch to low speed position. Connect test light between Brown wire terminal at low blower relay connector (located on auxiliary heater) and ground. If test light glows, go to next step. If test light does not glow, repair open Brown wire between low blower relay and splice near relay leads.
2. Connect test light between Dark Blue wire and Brown wire of low blower relay connector. If test light glows, go to next step. If test light does not glow, check for open Dark Blue wire between low blower relay connector and rear auxiliary heater control switch connector. If wire is okay, replace rear auxiliary heater control switch.
3. Connect test light between Red wire terminal at low blower relay connector and ground. If test light glows, go to next step. If test light does not glow, repair open Red wire between low blower relay and splice near relay leads.
4. Connect test light between Yellow wire terminal of low blower relay and ground. If test light glows, repair open Yellow wire between low blower relay connector and blower resistor connector. If test light does not glow, replace low blower relay.

FRONT VENTILATION CONTROLS DO NOT OPERATE

1. Ignition switch to ON. Disconnect front mode door motor connector. Connect un-powered test light between connector cavity 10 and ground. If test light is lit, go to next step. If test light is not lit, repair open in Circuit 141 (Brown wire) between instrument panel fuse block and splice S243. See WIRING DIAGRAMS.
2. Connect self-powered test light between front mode door motor connector cavity 7 and ground. If test light is lit, go to next step. If test light is not lit, repair open in circuit 141 (Black wire) between splice S244 and ground number G105.
3. Disconnect Connector C3 at HVAC Control module. Connect unpowered test light between cavity 5 (Brown wire) and ground. If test light is lit, go to next step. If test light is not lit, repair open in circuit 141 (Brown wire) between HVAC Control module and instrument panel fuse block.
4. Connect self-powered test light between HVAC connector cavity 2 (Black wire) and ground. If test light is lit, replace HVAC control module. If test light is not lit, repair open in circuit 150 (Black wire) between HVAC Control module and ground G200.

FRONT MODE DOOR MOTOR DOES NOT OPERATE

1. Ignition switch in ON. Disconnect front mode door motor connector. Move front blower switch on HVAC to LO. Observe that front blower motor is operating. Connect a DVOM from front mode door motor connector cavity 8 to ground. Move mode control dial while observing voltmeter response. If no voltage, erratic change or fixed voltage is observed, go to next step. If smooth voltage change is observed, go to step 5).
2. Disconnect connector C3 at HVAC module. Connect an un-powered test light from connector terminal 9 (White wire) and ground. If test light is not lit, go to next step. If test light is lit, repair short to voltage on White wire between HVAC module and front mode door motor.
3. Connect a self-powered test light between HVAC connector C3, terminal 9 (White wire) and ground. If test light is not lit, go to next step. If test light is lit, repair short to ground on White wire between HVAC module and front mode door motor.
4. Connect a self-powered test light between HVAC connector C3, terminal 9 (White wire) and front door motor connector terminal 8 (White wire). If test light is lit, replace HVAC module. If test light is not lit, repair open in White wire between HVAC module and front mode door motor.
5. Connect an un-powered test light between front mode door motor terminal 10 and ground. If test light is lit, go to next step. If test light is not lit, repair open in Brown wire between Splice S243 and front mode door motor.
6. Connect a self-powered test light between front mode door motor connector terminal 7 (Black wire) and ground. If test light is lit, replace front mode door motor. If test light is not lit, repair open in Black wire between front mode door motor and Splice S244.

FRONT TEMPERATURE DOOR MOTOR DOES NOT OPERATE

1. Ignition switch in ON. Disconnect front temperature door motor connector. Move front blower switch on HVAC to LO. Connect a DVOM from front mode door motor connector cavity 8 to ground. Move mode control dial while observing voltmeter response. If no voltage, erratic change or fixed voltage is observed, go to next step. If smooth voltage change is observed, go to step 5).
2. Disconnect connector C3 at HVAC module. Connect an un-powered test light from connector terminal 8 (Light Blue wire) and ground. If test light is not lit, go to next step. If test light is lit, repair short to voltage on Light Blue wire between HVAC module and front temperature door motor.
3. Connect a self-powered test light between HVAC connector C3, terminal 8 (Light Blue wire) and ground. If test light is not lit, go to next step. If test light is lit, repair short to ground on Light Blue wire between HVAC module and front temperature door motor.
4. Connect a self-powered test light between HVAC connector C3, terminal 8 (Light Blue wire) and front door motor connector terminal 8 (Light Blue wire). If test light is lit, replace HVAC module. If test light is not lit, repair open in White wire between HVAC module and front temperature door motor.
5. Connect an un-powered test light between front temperature door motor terminal 10 and ground. If test light is lit, go to next step. If test light is not lit, repair open in Brown wire between Splice S243 and front temperature door motor.
6. Connect a self-powered test light between front temperature door motor connector terminal 7 (Black wire) and ground. If test light is lit, replace front temperature door motor. If test light is not lit, repair open in Black wire between front temperature door motor and Splice S244.

RECIRCULATION DOOR MOTOR FAILS IN VENT POSITION

1. Ignition switch in ON. Disconnect recirculation door motor connector. Connect an un-powered test light between connector terminal 5 (Brown wire) and ground. If test light is lit go to next step. If test light is not lit, repair open in Brown wire between splice S243 and recirculation door motor.
2. Connect a powered test light between connector terminal 7 (Black wire) and ground. If test light is lit, go to next step. If test light is not lit, repair open in Black wire between recirculation door motor and splice S244.
3. Connect an un-powered test light between connector terminal 6 (Dark Green wire) and ground. Move front blower switch to LO. Confirm that front blower motor is operating. Actuate recirculation button on HVAC. If test light is not lit, go to next step. If test light is lit, replace recirculation door motor.
4. Disconnect HVAC connector C3. Connect a powered test light between terminal 4 (Dark Green wire) and recirculation door motor connector terminal 6 (Dark Green wire). If test light is lit, go to next step. If test light is not lit, repair open in Dark Green wire between HVAC module and recirculation door motor.
5. If vehicle is equipped with an auxiliary cooling fan, go to next step. If not, replace HVAC module.
6. Disconnect connector at auxiliary cooling fan A/C pressure switch. Connect a powered test light between auxiliary cooling fan A/C pressure switch connector terminal A and recirculation door motor connector terminal 6 (Dark Green wire). If test light is lit, replace HVAC module. If test light is not lit, repair open in Dark Green wire between auxiliary cooling fan A/C pressure switch and splice S212.

Note. Diode D101 may be open.

RECIRCULATION DOOR MOTOR FAILS IN RECIRCULATION POSITION

1. Ignition in ON. Move front blower switch in HI. Disconnect recirculation door motor connector. If door is not in recirculation position, go to next step. If door is still in recirculation position, replace motor.
2. Disconnect HVAC connector C3. Connect a powered test light between connector C3 terminal 4 (Dark Green wire) and ground. If test light is lit, go to next step. If test light is not lit, replace HVAC module.
3. For 7.4L, engine equipped vehicles with A/C, go to next step. On all other models, repair short to ground in Dark Green (circuit 1614) between HVAC module, auxiliary cooling fan A/C pressure switch, and recirculation door motor. If short is not found, check that diode D100 has not shorted.
4. Disconnect auxiliary cooling fan A/C pressure switch connector. Remove auxiliary cooling fan relay from its socket. Connect a powered test light between connector terminal A and ground. If test light is not lit, replace auxiliary cooling fan A/C pressure switch. If test light is lit, repair short to ground in Dark Green (circuit 1614) between HVAC module, auxiliary cooling fan A/C pressure switch, and recirculation door motor. If short is not found, check that diode D100 has not shorted.

FRONT MODE DOOR OPERATES WITH FRONT BLOWER SWITCH OFF

1. Ignition ON, move front blower switch in OFF. Disconnect HVAC connector C3. Connect un-powered test light between HVAC module connector terminal 3 (Dark Green wire) and ground. If test light is not lit, go to next step. If test light is lit, replace HVAC module.
2. Disconnect HVAC connector C2. Connect powered test light between connector C2 terminal D and connector C3 terminal 3. If light is lit, go to next step. If light is not lit, repair open in Dark Green wire (circuit 71) between connectors C2 and C3.
3. Connect an un-powered test light between connector C2 terminal G (Brown wire) and ground. If test light is lit, replace HVAC module. If test light is not lit, repair open in Brown wire between splice S268 and HVAC module connector C2.

REAR VENTILATION CONTROLS DO NOT OPERATE FROM EITHER CONTROL MODULE

1. Ignition ON, disconnect connector at rear auxiliary mode door motor. Connect un-powered test light between connector terminal 10 (Brown wire) and ground. If test light is lit, go to next step. If test light is not lit, repair open in Brown wire (circuit 141) between I/P fuse block and splice S400.
2. Connect a powered test light between rear auxiliary mode door motor connector terminal 7 (Black wire) and ground. If test light is lit, go to next step. If test light is not lit, repair open in Black wire (circuit 150) between splice S403 and ground G400.
3. Disconnect front auxiliary HVAC connector. Connect an un-powered test light between front auxiliary HVAC connector terminal G and ground. If test light is lit, go to next step. If test light is not lit, repair open in Brown wire (circuit 141) between splice S310 and splice S308.
4. Connect powered test light between front auxiliary heater and A/C control module connector terminal B (Black wire) and ground. If test light is lit, replace auxiliary HVAC control logic module. If test light is not lit, repair open in Black wire (circuit 150) between splice S307 and splice S410.

REAR AUXILIARY MODE DOOR DOES NOT OPERATE FROM EITHER CONTROL MODULE

1. Ignition ON. Move blower switch to OFF. Disconnect rear auxiliary mode door motor connector. Connect un-powered test light between rear auxiliary mode door motor connector terminal 10 (Brown wire) and ground. If test light is lit, go to next step. If test light is not lit, repair open in Brown wire between splice S400 and rear auxiliary mode door motor.
2. Connect powered test light between rear auxiliary mode door motor connector terminal 7 (Black wire) and ground. If test light is lit, go to next step. If test light is not lit, repair open in Black wire (circuit 150) between rear auxiliary mode door motor and splice S403.
3. Connect DVOM between rear auxiliary mode door motor connector terminal 8 and ground. Adjust position of mode control dial at front auxiliary HVAC module while observing DVOM. If no voltage, erratic voltage or fixed voltage is observed, go to next step. If smoothly variable voltage is observed, replace rear auxiliary mode door motor.
4. Disconnect auxiliary HVAC control logic module connector. Connect and un-powered test lamp between connector terminal F (White wire) and ground. If test light is not lit, go to next step. If test light is lit, repair short to voltage on White wire (circuit 119)between auxiliary HVAC control logic module and rear auxiliary mode door motor.
5. Connect powered test light between auxiliary HVAC control logic module connector terminal F and ground. If test light is not lit, go to next step. If test light is lit, repair short to ground on White wire (circuit 119) between auxiliary HVAC control logic module and rear auxiliary mode door motor.
6. Connect powered test light between auxiliary HVAC control logic module connector terminal F and rear auxiliary mode door motor connector terminal 8. If test light is lit, replace auxiliary HVAC control logic module. If test light is not lit, repair open in White wire (circuit 119) between auxiliary HVAC control logic module and rear auxiliary mode door motor.

REAR AUX TEMP DOOR DOES NOT OPERATE FROM EITHER CONTROL MODULE

1. Ignition ON. Move blower switch to OFF. Disconnect rear auxiliary temperature door motor connector. Connect un-powered test light between rear auxiliary mode door motor connector terminal 10 (Brown wire) and ground. If test light is lit, go to next step. If test light is not lit, repair open in Brown wire between splice S400 and rear auxiliary temperature door motor.
2. Connect powered test light between rear auxiliary temperature door motor connector terminal 7 (Black wire) and ground. If test light is lit, go to next step. If test light is not lit, repair open in Black wire (circuit 150) between rear auxiliary temperature door motor and splice S403.
3. Connect DVOM between rear auxiliary temperature door motor connector terminal 8 and ground. Adjust position of mode control dial at front auxiliary HVAC module while observing DVOM. If no voltage, erratic voltage or fixed voltage is observed, go to next step. If smoothly variable voltage is observed, replace rear auxiliary temperature door motor.
4. Disconnect auxiliary HVAC control logic module connector. Connect un-powered test lamp between connector terminal B (Dark Blue wire) and ground. If test light is not lit, go to next step. If test light is lit, repair short to voltage on Dark Blue wire (circuit 1199) between auxiliary HVAC control logic module and rear auxiliary temperature door motor.
5. Connect powered test light between auxiliary HVAC control logic module connector terminal B and ground. If test light is not lit, go to next step. If test light is lit, repair short to ground on Dark Blue wire (circuit 1199) between auxiliary HVAC control logic module and rear auxiliary temperature door motor.
6. Connect powered test light between auxiliary HVAC control logic module connector terminal F and rear auxiliary temperature door motor connector terminal 8. If test light is lit, replace auxiliary HVAC control logic module. If test light is not lit, repair open in Dark Blue wire (circuit 1199) between auxiliary HVAC control logic module and rear auxiliary temperature door motor.

REAR CONTROL MODULE DOES NOT CONTROL REAR AUXILIARY DOORS

1. Ignition ON, disconnect front auxiliary HVAC control module connector. Disconnect auxiliary HVAC control logic module connector. Connect powered test light between front auxiliary HVAC module connector terminal F and auxiliary HVAC control logic module connector terminal M. If test light is lit, go to next step. If test light is not lit, repair open in Orange wire (circuit 1923) between auxiliary HVAC control logic module and auxiliary HVAC control logic module.
2. Connect un-powered test light between auxiliary HVAC control logic module connector terminal J and ground. If test light is lit, go to next step. If test light is not lit, repair open in Brown wire (circuit 341) between splice S308 and auxiliary HVAC control logic module.
3. Connect fused jumper wire from auxiliary HVAC logic module pin M to ground. Connect fused jumper wire from auxiliary HVAC control logic module pin J to positive battery voltage. Connect powered test light between auxiliary HVAC logic module pins D and B. If test light is lit, go to next step. If test light is not lit, replace auxiliary HVAC control logic module.
4. Disconnect rear auxiliary HVAC control module connector. Connect un-powered test light between rear auxiliary HVAC control module connector terminal G and ground. If test light is lit, go to next step. If test light is not lit, repair open in Brown wire (circuit 341) between splice S308 and rear auxiliary HVAC module.
5. Connect powered test light between rear auxiliary HVAC control module connector terminal B and ground. If test light is lit, replace rear auxiliary HVAC control module. If test light is not lit, repair open in Black wire (circuit 150) between rear auxiliary HVAC control module and splice S307.

FRONT CONTROL MODULE DOES NOT CONTROL REAR AUXILIARY DOORS

1. Ignition ON, disconnect front auxiliary HVAC control module connector. Connect un-powered test light between front auxiliary HVAC control module connector terminal G and ground. If test light is lit, go to next step. If test light is not lit, repair open in Brown wire (circuit 341) between splice S308 and front auxiliary HVAC control module.
2. Connect powered test light between front auxiliary HVAC control module connector terminal B and ground. If test light is lit, replace front auxiliary HVAC control module. If test light is not lit, repair open in Black wire (circuit 150) between front auxiliary HVAC control module and splice S307.

REAR AUXILIARY MODE DOOR MOTOR DOES NOT OPERATE FROM FRONT CONTROL MODULE

1. Ignition ON, disconnect auxiliary HVAC control logic module connector. Connect a DVOM from auxiliary HVAC control logic module connector terminal E to ground. Adjust mode control dial of auxiliary HVAC control module while monitoring DVOM. If no voltage, erratic voltage or fixed voltage are observed, go to next step. If smooth variable voltage is observed, replace auxiliary HVAC control logic module.
2. Disconnect front auxiliary HVAC control module connector. Connect an un-powered test light between connector terminal J and ground. If test light is not lit, go to next step. If test light is lit, repair short to voltage in Light Blue wire (circuit 919) between front auxiliary HVAC control module and auxiliary HVAC control logic module.
3. Connect powered test light between front auxiliary HVAC control module connector terminal J and ground. If test light is not lit, go to next step. If test light is lit, repair short to ground in Light Blue wire (circuit 919) between front auxiliary HVAC control module and auxiliary HVAC control logic module.
4. Connect powered test light between front auxiliary HVAC control module connector terminal J and auxiliary HVAC control logic module connector terminal E. If test light is lit, replace front auxiliary HVAC control module. If test light is not lit, repair open in Light Blue wire (circuit 919) between front auxiliary HVAC control module and auxiliary HVAC control logic module.

REAR AUXILIARY TEMP DOOR MOTOR DOES NOT OPERATE FROM FRONT CONTROL MODULE

1. Ignition ON. Disconnect auxiliary HVAC control logic module connector. Connect DVOM from auxiliary HVAC control logic module connector terminal A to ground. Adjust temperature control dial at front auxiliary HVAC control module while monitoring DVOM. If no voltage, erratic voltage or fixed voltage are observed, go to next step. If smooth variable voltage is observed, replace auxiliary HVAC control logic module.
2. Disconnect front auxiliary HVAC control module connector. Connect un-powered test light between front auxiliary HVAC control module connector terminal H and ground. If test light is not lit, go to next step. If test light is lit, repair short to voltage on Light Blue wire (circuit 733) between front auxiliary HVAC control module and auxiliary HVAC control logic module.
3. Connect powered test light between front auxiliary HVAC control module connector terminal H and ground. If test light is not lit, go to next step. If test light is lit, repair short to ground on Light Blue wire (circuit 733) between front auxiliary HVAC control module and auxiliary HVAC control logic module.
4. Connect powered test light between front auxiliary HVAC control module connector terminal H and A/C Control Logic Module Connector Terminal A. If test light is not lit, replace front auxiliary HVAC control module. If test light is lit, repair open in Light Blue wire (circuit 733) between front auxiliary HVAC control module and auxiliary HVAC control logic module.

REAR AUXILIARY MODE DOOR MOTOR DOES NOT OPERATE FROM REAR CONTROL MODULE

1. Ignition ON. Disconnect auxiliary HVAC control logic module connector. Connect DVOM from auxiliary HVAC control logic module connector terminal D to ground. Adjust mode control dial at rear auxiliary HVAC control module while monitoring DVOM. If no voltage, erratic voltage or fixed voltage are observed, go to next step. If smooth variable voltage is observed, replace auxiliary HVAC control logic module.
2. Disconnect rear auxiliary HVAC control module connector. Connect un-powered test light between rear auxiliary HVAC control module connector terminal J and ground. If test light is not lit, go to next step. If test light is lit, repair short to voltage on Light Blue wire (circuit 920) between rear auxiliary HVAC control module and auxiliary HVAC control logic module.
3. Connect powered test light between rear auxiliary HVAC control module connector terminal J and ground. If test light is not lit, go to next step. If test light is lit, repair short to ground on Light Blue wire (circuit 920) between rear auxiliary HVAC control module and auxiliary HVAC control logic module.
4. Connect powered test light between rear auxiliary HVAC control module connector terminal J and A/C Control Logic Module Connector Terminal D. If test light is not lit, replace rear auxiliary HVAC control module. If test light is lit, repair open in Light Blue wire (circuit 920) between rear auxiliary HVAC control module and auxiliary HVAC control logic module.

REAR AUXILIARY TEMP DOOR MOTOR DOES NOT OPERATE FROM REAR CONTROL MODULE

1. Ignition ON. Disconnect auxiliary HVAC control logic module connector. Connect DVOM from auxiliary HVAC control logic module connector terminal C to ground. Adjust temperature control dial at rear auxiliary HVAC control module while monitoring DVOM. If no voltage, erratic voltage or fixed voltage are observed, go to next step. If smooth variable voltage is observed, replace auxiliary HVAC control logic module.
2. Disconnect rear auxiliary HVAC control module connector. Connect un-powered test light between front auxiliary HVAC control module connector terminal H and ground. If test light is not lit, go to next step. If test light is lit, repair short to voltage on Light Blue wire (circuit 1646) between rear auxiliary HVAC control module and auxiliary HVAC control logic module.
3. Connect powered test light between rear auxiliary HVAC control module connector terminal H and ground. If test light is not lit, go to next step. If test light is lit, repair short to ground on Light Blue wire (circuit 1646) between rear auxiliary HVAC control module and auxiliary HVAC control logic module.
4. Connect powered test light between rear auxiliary HVAC control module connector terminal H and A/C Control Logic Module Connector Terminal C. If test light is not lit, replace rear auxiliary HVAC control module. If test light is lit, repair open in Light Blue wire (circuit 1646) between rear auxiliary HVAC control module and auxiliary HVAC control logic module.

Scheme 1

Scheme 2

REMOVAL & INSTALLATION

1. Disconnect negative battery cable. Remove glove box. Remove front screw from right door sill plate. Remove right cowl kick panel. Unplug connector from Electronic Control Module (ECM) if necessary. Unplug connector from blower motor. Remove blower motor cover and cooling tube.
2. Remove bolt from right dash support. Remove blower motor flange screws. Pull blower motor forward carefully to avoid distorting blower fan. Remove blower motor. To install, reverse removal procedure.

1. Disconnect negative battery cable. Remove instrument panel bezel. Remove control assembly screws. Pull control assembly away from instrument panel.
2. Disconnect control cables. Unplug connectors. Remove control assembly. Remove blower switch knob and retaining clip. Remove blower switch. To install, reverse removal procedure.

HEATER CORE

1. Disconnect negative battery cable. Remove glove box. Remove center floor duct. Remove Electronic Control Module (ECM) and tray. Remove kick panel. Remove blower motor cover and blower motor.
2. Remove steering column. Tilt dash panel back. Remove coolant recovery reservoir. Drain engine coolant. Disconnect heater hoses at core. Remove heater case. Remove heater case cover plate.
3. Remove screws and bracket attaching core to case. (Scheme 3) Remove heater core. To install, reverse removal procedure. Fill cooling system. Start engine and check for leaks.

Scheme 3

Disconnect negative battery cable. Remove instrument panel bezel. Remove control assembly screws. Disconnect cables from control assembly. (Scheme 4) Remove glove box and glove box door as an assembly. Remove cable retaining clip. Disconnect cables. To install, reverse removal procedure. Check cable operation.

Scheme 4

Disconnect negative battery cable. Remove right rear trim panel cover. Unplug electrical connector. Remove blower motor. To install, reverse removal procedure.

1. Disconnect negative battery cable. On vehicles with switch mounted overhead, go to next step. On vehicles with switch mounted on instrument panel, remove instrument panel bezel. Unplug connector. Remove control switch. To install, reverse removal procedure.
2. Remove overhead console (if necessary). Unplug connectors from control assembly. Remove screws and control assembly. Remove switch. To install, reverse removal procedure.

Disconnect negative battery cable. Drain engine coolant. Remove right rear wheelwell panel. Remove right rear trim panel cover. Disconnect heater hoses from heater core. Unplug connector from heater assembly. Remove heater case cover. Remove heater core. To install, reverse removal procedure. Fill cooling system. Start engine and check for leaks.

TORQUE SPECIFICATIONS

TORQUE SPECIFICATIONS

See also:
• A/C-HEATER SYSTEM