Heater System GMC Sonoma Syclone

MODEL IDENTIFICATION

Adjustment and repair procedures in this article are referred to by model name or series. Following table lists General Motors model name and series designation.

GENERAL MOTORS MODEL DESIGNATION

GENERAL MOTORS MODEL DESIGNATION

DESCRIPTION

System is a blend-air type. Outside air is heated and then mixed with cooler outside air to attain desired temperature. System consists of a blower, air inlet assembly, heater air distributor assembly and heater control panel.

Blower, air inlet assembly and heater hoses are located on engine side of firewall, while heater core and distributor duct are on passenger side. System has no heater control valve. Coolant circulation keeps heater core hot at all times.

Operation of blower motor is controlled by fan switch. Motor is connected in series with fan switch and blower resistor assembly.

On Van and Suburban models, an auxiliary heater is available for heating rear of vehicle. Unit operates independently of standard heater and has its own set of controls. Heater hoses connect at standard heater and extend to auxiliary heater. A vacuum-operated heater control valve is installed in inlet line in engine compartment to cut off coolant flow when heat is not desired. (Scheme 8)and (Scheme 9).

TEMPERATURE CONTROL LEVER

On C, K, R, V, P, and G series, lower lever on control panel controls discharge air temperature in all mode positions. Full right position provides maximum heat. Full left position provides cool (outside) air. On L, M, S and T series, operation is the same, except left lever has maximum heat position at top and cool position at bottom.

MODE CONTROL LEVER OPERATION (C/K/R/V/P/G SERIES)

When lever is in vent position (if equipped), all discharge air is directed to upper outlets. DEF (defrost) position directs most air to windshield (defroster) outlets with some air directed into floor (heater) outlets. When in HEATER position, most air is delivered through floor outlets with some airflow to windshield outlets. On L, M, S and T series, operation is the same, except right lever has defrost position at top and vent position at bottom.

BLOWER CONTROLS OPERATION (C/K/R/V/P/G SERIES)

Blower control can be either knob or lever type. Knob is a 4-speed type rotating from OFF to HI. Lever is a variable speed type, sliding from OFF through LO to HI. On L, M, S and T series, operation is the same except controls run vertically with blower switch at top.

AUX HEATER SWITCH OPERATION (C/K/R/V/P/G SERIES)

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 will not operate. On L, M, S and T series, operation is the same except controls run vertically with blower switch at top. Left lever is temperature control with maximum heat at top and cool at bottom. Right lever is mode lever with defrost at top and vent at bottom.

CONTROL CABLES ADJUSTMENT (C/K SERIES)

Cables are not adjustable.

CONTROL CABLES ADJUSTMENT (P/R/V SERIES)

Disconnect battery ground cable. Remove glove box and glove box door assembly. Pry off cable clip eyelet with pliers, and disconnect cable from door. Remove cable retaining screw. While holding cable with pliers, rotate mounting tab on cable to lengthen or shorten cable.

CONTROL CABLES ADJUSTMENT (L/M/G SERIES)

Attach cable core wire and cable housing to control panel. Move temperature control lever to cool position, and attach loop on cable core wire to temperature door on heater case. Attach cable housing to heater/defroster assembly. To adjust cable, move temperature control lever to full heat position.

CONTROL CABLES ADJUSTMENT (S/T SERIES)

Remove control panel. Disconnect control cables at both ends. Replace cables and install control panel. Cycle control lever through its full range of travel to adjust cable.

TROUBLE SHOOTING

Note. See appropriate TROUBLE SHOOTING article in this section.

CONTROL PANEL R & I (C/K/L/M/P/R/V SERIES)

Disconnect battery ground cable. Remove instrument panel bezel. Disconnect control cables and blower switch electrical connectors. Remove control panel through opening above it. Remove blower switch attaching screws, and remove blower switch. To install, reverse removal procedure.

CONTROL PANEL R & I (G SERIES)

1. Disconnect battery ground cable. Remove instrument panel bezel. Remove control panel-to-instrument panel retaining screws. Carefully pull control panel rearward far enough to gain access to cables.
2. Disconnect control cables, light bulb and blower switch connector. Remove control panel from vehicle. Remove blower switch attaching screws, and remove blower switch. To install, reverse removal procedure.

CONTROL PANEL R & I (S/T SERIES)

Disconnect battery ground cable. Remove instrument panel center bezel. Remove control panel screws and pull out control panel. Disconnect electrical connection and cables from control panel. Remove blower switch from control panel. To install, reverse removal procedure.

HEATER CORE R & I (C/K SERIES)

1. Disconnect battery ground cable. Drain cooling system. Remove seven screws retaining heater case cover plate, and remove cover plate. Disconnect heater hoses at core. CAUTION: Heater core can be damaged if too much force is applied to heater core pipes during hose removal.
2. Drain coolant into pan, and plug openings. Remove screws and bracket attaching core to case. Remove core. To install, reverse removal procedure. (Scheme 1)

Scheme 1

HEATER CORE R & I (G SERIES)

1. Disconnect battery ground cable. Drain cooling system. Remove coolant recovery tank. Disconnect heater hoses at core. Drain coolant into pan, and plug openings. Remove screws attaching heater duct at case and engine cover. Remove duct.
2. Remove engine housing cover. Remove instrument panel attaching screws at windshield. Remove all lower screws and right lower instrument panel support bracket at door pillar. Remove engine cover. Lower steering column, and then raise and support right side of instrument panel.
3. Remove screw attaching defroster duct to heater distributor case and screws attaching heater distributor to heater case. Disconnect temperature door cable and bolt back cable to provide access. Remove nuts at engine compartment side of heater distributor case, and remove nut on passenger compartment side.
4. Remove heater case and core as an assembly. Tilt case assembly rearward at top, while lifting upward until core tubes clear dash openings. Remove core retaining straps, and remove core. To install, reverse removal procedure. Ensure seals are intact before installing.

HEATER CORE R & I (L/M SERIES)

Disconnect battery ground cable. Drain coolant. Remove heater hoses at core and plug openings. Remove core cover attaching screws. Remove heater core retaining straps and remove core. To install, reverse removal procedure. (Scheme 2)

Scheme 2

HEATER CORE R & I (P/R/V SERIES)

1. Disconnect battery ground cable. Drain cooling system. Disconnect heater hoses at heater core, drain core into pan and plug openings. Remove nuts from heater distributor duct studs. Remove glove box and glove box door assembly. Disconnect control cables.
2. Remove floor outlet. Remove defroster duct-to-heater distributor duct screw. Remove heater distributor-to-firewall screws. Pull assembly rearward to gain access to wiring harness. Disconnect all harness connectors attached to assembly.
3. Remove assembly from vehicle. Remove heater core retaining straps, and remove cores. To install, reverse removal procedure. Ensure seals are intact before installing.

HEATER CORE R & I (S/T SERIES)

Disconnect battery ground cable. Drain engine coolant. Remove heater core hoses at core, and plug core openings. Remove core cover attaching screws. Remove retainers at end of core. Remove core from vehicle. To install, reverse removal procedure. (Scheme 3)

Scheme 3

BLOWER MOTOR R & I (C/K SERIES)

Disconnect battery ground cable. Remove front screw from right door sill plate. Remove right cowl kick panel. Disconnect electrical connector from blower motor. Remove blower motor cooling tube. Loosen courtesy light screws, and move light aside (if equipped). Remove bolt from right dash support. Remove blower motor flange screws. Pull blower motor forward carefully to avoid distorting blower fan. Remove blower. To install, reverse removal procedure.

BLOWER MOTOR R & I (G/P/R/V SERIES)

Disconnect battery ground cable. On G Series, remove coolant recovery tank, and remove power antenna. On all models, disconnect blower motor lead wire. Remove blower motor mounting screws. Remove motor and fan. If necessary, pry gently on blower flange to remove. Remove blower fan-to-motor shaft nut and remove fan. To install, reverse removal procedure.

BLOWER MOTOR R & I (L/M SERIES)

Disconnect negative battery cable. Disconnect blower electrical connections, and remove coolant recovery bottle. Remove bolts from washer bottle, and move out of way. Remove blower motor retaining screws and remove blower. To install, reverse removal procedure.

BLOWER MOTOR R & I (S/T SERIES)

Disconnect negative battery cable. Disconnect electrical connectors at blower motor. Remove blower motor retaining screws, and remove blower motor. To install, reverse removal procedure.

CONTROL CABLES R & I (C/K/P/R/V SERIES)

Disconnect battery ground cable. Remove instrument panel bezel. Remove screws attaching control panel to instrument panel. Raise lower control panel and remove cable push nuts and tab attaching screws. Remove glove box and glove box door as an assembly. Remove cable from retaining clip, and remove cable assembly. To install, reverse removal procedure. Check operation and adjust if necessary. (Scheme 4)and (Scheme 5).

CONTROL CABLES R & I (G SERIES)

1. Disconnect battery ground cable. Remove glove box assembly. Using pliers, pry off cable clip eyelet clip from control assembly and heater/defrost assembly. Unsnap flags from receivers on heater/defroster assembly and control panel assembly.
2. Remove cable retaining screws on back of heater/defroster assembly. To install, reverse removal procedure. Test operation and adjust if necessary.

CONTROL CABLES R & I (L/M/S/T SERIES)

Disconnect negative battery cable. Pull control panel out from dash. Disconnect cables at control panel and heater module. Remove cables. To install, reverse removal procedure. (Scheme 6)and (Scheme 7).

Scheme 4

Scheme 5

Scheme 6

Scheme 7

Scheme 8

Scheme 9

Rear Heater Wiring Diagram (P, R & V Series). Scheme 10