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 and an air inlet assembly, heater air distributor assembly and heater control panel.
Blower and air inlet assembly and heater hoses are located on the engine side of dash panel 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 the fan switch. The motor is connected in series with the fan switch and blower resistor assembly.
On the Van models, an auxiliary heater is available for heating rear of vehicle. (Scheme 3) The unit operates independently of standard heater and has its own set of controls. Heater hoses connect at the standard heater and extend from the standard heater to the auxiliary heater. A vacuum-operated heater control valve is installed in the inlet line in the engine compartment to cut off coolant flow when heat is not desired.
Temperature Control Lever
The lower lever on the control panel controls discharge air temperature in all Mode Control Lever positions. Full right position provides maximum heat. Full left position provides cool (outside) air.
Mode Control Lever (Standard System)
When in "OFF" position, the system is off. When in "HEATER" position, most of the air is delivered through the floor (heater) outlet with some air flow to the windshield (defroster) outlets.
The lever may be adjusted between "HEATER" and "DEF" to vary air distribution between floor air outlet and windshield outlet. In the "DEF" position, heated air is delivered to the windshield outlets with a small amount to the floor outlets.
Mode Control Lever (Optional System - Astro Van Models)
When this lever is in the "VENT" position, all discharge air is directed to the upper outlets. The "DEF" position directs most of the air to the windshield (defroster) outlets with some directed to the floor (heater) outlets. When in "HEATER" position, most of the air is delivered through the floor outlets with some air flow to the windshield outlets.
Blower Control
Blower control can be either knob or lever. Knob is a 4-speed type rotating from "OFF" to "HI". Lever is a variable speed type, sliding from "OFF" through "LO" to "HI".
Auxiliary Heater Blower Switch
A 3-speed blower switch is located in the instrument panel to the right of steering column. When switch is in "OFF" position, auxiliary system will not operate.
Heater Control Panels. Scheme 3
Astro Van Auxiliary Heater. Scheme 4
Blazer & Pickup Models
Disconnect battery ground. Remove glove box and glove box door assembly. Pry off cable clip eyelet with pliers and disconnect cable from the door. Remove cable retaining screw. While holding cable with pliers, rotate the mounting tab on cable by reversing removal procedure. (Scheme 5)
"G" Series & Astro Van Models
Attach cable core wire and cable housing to control panel. Move temperature control lever to cool position and and attach loop on cable core wire to temperature door on heater case. Attach cable housing to heater/defroster assembly. Move temperature control lever to full heat position to adjust cable. (Scheme 6)
TROUBLE SHOOTING & DIAGNOSIS
See the GENERAL MOTORS HEATERS - TROUBLE SHOOTING & DIAGNOSIS article.
Removal & Installation (Blazer, Pickup & Astro Van Models)
Disconnect battery ground. 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 blower switch. Reverse removal procedure to install.
Removal & Installation ("G" Series Van Models)
- Disconnect battery ground. Remove instrument panel bezel. Remove control panel-to-instrument panel retaining screws and carefully pull control panel rearward far enough to gain access to cables.
- 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.
HEATER CORE
Note. These procedures are for vehicles with heater systems only. For vehicles with manual A/C-heater systems, see appropriate article in MANUAL A/C SYSTEMS section.
Removal & Installation (Blazer & Pickup Models)
- 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.
- Remove floor outlet and remove defroster duct-to-heater distributor duct screw. Remove heater distributor-to-dash panel screws. Pull assembly rearward to gain access to wiring harness and disconnect all harness connectors attached to assembly.
- Remove assembly from vehicle. Remove heater core retaining straps and remove core. To install, reverse removal procedure. Make sure seals are intact before installing.
- Disconnect battery ground. Drain cooling system. Remove coolant recovery tank. Disconnect heater hoses at core, drain coolant into pan and plug openings. Remove screws attaching heater duct to case and distributor duct to engine cover. Remove duct.
- Remove engine housing cover. Remove instrument panel attaching screws at windshield, all lower screws and right lower instrument panel support bracket at door pillar and engine housing. Lower steering column, then raise and support right side of instrument panel.
- Remove defroster duct to distributor case attaching screw and 2 screws attaching distributor to heater case. Disconnect temperature door cable and fold back cable to provide access. (Scheme 6) Remove 3 nuts at engine compartment side of distributor case and 1 on passenger compartment side.
- Remove heater case and core as an assembly. Tilt case assembly rearward at top while lifting up until core tubes clear dash openings. Remove core retaining straps and remove core. To install, reverse removal procedure. Make sure seals are intact before installing.
Removal & Installation (Astro Van Models)
Disconnect battery ground. Drain coolant. Remove coolant bottle. Remove 2 bolts from washer bottle and move out of way. Remove heater hoses at core and plug openings. Remove core cover attaching screws. Remove heater core retainer straps and remove core To install, reverse removal procedure.
Removal & Installation (Blazer, Pickup & "G" Series Van Models)
Disconnect battery ground. On Vans remove coolant recovery tank and power antenna. On all models disconnect blower motor lead wire. Remove 5 blower motor mounting screws and remove motor and wheel. If necessary, pry gently on the blower flange to remove. Remove the blower wheel-to-motor shaft nut and remove wheel from shaft. To install, reverse removal procedure.
Disconnect negative battery cable. Disconnect blower electrical connections and remove coolant bottle. Remove two bolts from washer bottle and move out of way. Remove blower motor retaining screws and remove blower. To install, reverse removal procedure.
Disconnect battery ground. Remove instrument panel bezel. Remove screws attaching control panel to instrument panel. Raise lower control 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.
Control Cable Routing (Blazer and Pickup Models). Scheme 5
- Disconnect battery ground. Remove glove box and glove box door assembly. Pry off cable clip eyelet clip from control assembly and heater/defroster assembly with pliers. Unsnap flags from receivers on heater/defroster assembly and control assembly.
- Remove cable retaining screws on back of heater/defroster assembly. Reinstall cable by reversing removal procedure. Test operation and adjust if necessary. (Scheme 6)
Control Cable Routing ("G" Series Van Models). Scheme 6
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.
