A/c-Heater System - Manual GMC Cab & Chassis S15

DESCRIPTION

Integral A/C-heater system is a blend-air system. Air entering the vehicle must pass through the evaporator core, and through or around the heater core to provide air of the desired temperature. Compressor operation is controlled by a pressure sensing switch on top of the accumulator.

Auxiliary A/C systems are available. These systems operate in conjunction with the main system, and provide air conditioning only (auxiliary heater is a separate unit). Rear blower speed is independent of main system control. Rear blower may be operated even when front blower is off.

Mode Control Lever

Mode lever controls a vacuum operated selector valve to operate air door motors, providing desired air distribution. It also allows for selection of air conditioning or heating functions, including defroster air distribution.

Temperature Control Lever

Temperature control lever regulates the temperature of air entering passenger compartment through a cable operating the blend-air door. In "COLD" position, air by-passes the heater core to provide maximum cooling.

In other positions, air chilled by the evaporator core and heated air from the heater core are mixed to provide air of the desired temperature. In "HOT" position, A/C system should be off to provide maximum heating.

Blower Switch

Blower switch is a 4-position lever with "LOW", "HI" and 2 intermediate positions. Blower operates in any mode lever position except "OFF".

Auxiliary Blower Switch

Blower switch is the only control provided for auxiliary A/C system. In the "OFF" position, blower is inoperative, even though refrigerant is circulating through evaporator core if main system is operating. To operate auxiliary system, simply select desired blower speed. Auxiliary blower may be used for air circulation when main system is not in A/C mode.

TEMPERATURE CONTROL CABLE

Remove glove box and door. Loosen cable attaching screw at selector duct assembly. Make sure cable is installed in bracket on selector duct assembly. Place temperature selector lever in full "COLD" position and hold while tightening cable attachment screw.

TROUBLE SHOOTING & DIAGNOSIS

See General Motors Manual A/C - TROUBLE SHOOTING & DIAGNOSIS in this section.

Removal

1. Disconnect battery ground and compressor clutch connector. Discharge system using approved refrigerant recovery/recycling equipment. Disconnect accumulator inlet and outlet lines and cap or plug openings.
2. Remove accumulator bracket screws and remove accumulator from vehicle. Drain refrigerant oil from accumulator and measure quantity drained.

Installation

1. Measure an amount of clean refrigerant oil equal to that drained from accumulator and add an additional one oz. oil (2 oz. on "S" series vehicles). Uncap new accumulator and add oil.
2. To complete installation, reverse removal procedure, using new "O" rings lubricated with clean refrigerant oil. Leak test, evacuate and recharge system.

Removal & Installation

1. Disconnect battery ground. Disconnect blower motor wires. Disconnect blower motor cooling tube. On Van models, remove coolant recovery tank and power antenna.
2. On all models, remove screws attaching blower motor to case and remove blower assembly. Remove nut attaching blower wheel to motor shaft and separate. To install, reverse removal procedure, using new sealant if necessary.

Blower Motor Installation "C" and "K" models shown. "G" and "S" models similar. Scheme 1

1. Disconnect battery ground. Disconnect rear duct assembly. Disconnect blower motor ground strap and lead wire. Support case assembly.
2. Remove lower-to-upper blower-evaporator case screws and lower the case and blower motor assembly. Remove retaining strap and remove motor and wheels. Remove wheels from motor shaft.
3. To install, position wheels on motor shaft making sure tension springs are installed on wheel hubs. Reverse removal procedure to complete installation, aligning wheels so they do not contact case. (Scheme 2)

Auxiliary Blower Motor Wheels Installation Rotate wheels to ensure they do not rub case. Scheme 2

1. Disconnect battery ground. Discharge refrigerant system using approved refrigerant recovery/recycling equipment. Remove grille. Remove radiator grille center support. Remove left grille from upper fender support. Disconnect condenser inlet and outlet lines and cap openings. Remove condenser-to-radiator support screws.
2. Bend the left grille support outboard to gain clearance. Remove condenser from vehicle by pulling forward and lowering. To install, reverse removal procedure, using new "O" rings lubricated with clean refrigerant oil. Add one oz. clean refrigerant oil to condenser. Leak test, evacuate and recharge system.

1. Disconnect battery ground. Remove radio. Remove instrument panel bezel. Remove control panel attaching screws and pull control panel out far enough to gain access to back of control panel.
2. Disconnect control cable, vacuum harness and electrical connectors at control panel. Remove control panel from vehicle. To install, reverse removal procedure.

Discharge refrigerant system using approved refrigerant recovery/recycling equipment. Disconnect liquid line from the evaporator inlet. Cap opening on line. Using needle-nose pliers, remove expansion tube from evaporator core inlet line.

To install, reverse removal procedure, using new "O" rings lubricated with clean refrigerant oil. Insert the short screen end of the tube into the evaporator inlet line. (Scheme 3) Leak test, evacuate and recharge system.

Cutaway View of Expansion (Orifice) Tube Install short screen end to inlet line. Scheme 3

EXPANSION VALVE

Note. Expansion valve is used on auxiliary units, which do not use external equalizer line.

1. Disconnect battery ground. Discharge refrigerant system using approved refrigerant recovery/recycling equipment. Remove rear duct. Disconnect blower motor ground and lead wires. Support lower case and motor. Remove screws attaching case halves and lower case and motor assembly. Remove expansion valve sensing bulb clamps.
2. Disconnect valve inlet and outlet lines and remove expansion valve. Cap open connections. To install, reverse removal procedure, using new "O" rings lubricated with clean refrigerant oil. Make sure bulb makes good contact with core outlet line. Leak test, evacuate and recharge system.

Expansion Valve Installation. Scheme 4

1. Disconnect the battery ground. Discharge refrigerant system using approved refrigerant recovery/recycling equipment. Remove nuts from selector duct studs projecting through the dash panel. Remove cover-to-dash and cover-to-case screws and remove evaporator case cover. Disconnect evaporator core inlet and outlet lines and cap openings.
2. Remove expansion tube. Remove evaporator core assembly. To install, reverse removal procedure, using new "O" rings lubricated with clean refrigerant oil. Add 3 oz. clean refrigerant oil to evaporator. Leak test, evacuate and recharge system.

1. Disconnect battery ground. Discharge refrigerant system using approved refrigerant recovery/recycling equipment. Remove rear duct. Disconnect blower motor ground and lead wires. Disconnect refrigerant lines at rear of evaporator-blower assembly. Cap openings. Remove screws attaching evaporator-blower assembly to roof rail.
2. Lower evaporator-blower assembly and place on a work bench upside down. Remove case half attaching screws and remove upper case half from evaporator core. Remove expansion valve inlet and outlet lines and cap openings. Remove expansion valve capillary bulb from evaporator outlet line and remove valve.
3. Remove plastic pins holding screen to core and remove screen. To install, reverse removal procedure, using new "O" rings lubricated with clean refrigerant oil. Make sure capillary bulb has good contact with line. Add 3 oz. clean refrigerant oil to new core. Leak test, evacuate and recharge system.

Auxiliary Blower-Evaporator Assembly. Scheme 5

Disconnect battery ground. Disconnect drain tube from rear duct. Remove screws attaching duct to roof panel and rear header brackets. Remove duct. To install, reverse removal procedure.

HEATER CORE

Note. These procedures are for vehicles with manual A/C-heater systems only. For replacement on vehicles equipped with heater systems, see appropriate article in 1986 GENERAL MOTORS - HEATER SYSTEMS section.

1. Disconnect battery ground. Drain radiator and disconnect heater hoses from heater core. Plug openings. Remove glove box and door. Remove screws attaching center duct to selector duct and instrument panel. Remove center ducts (lower and upper). Disconnect temperature control cable at blend-air door.
2. Remove nuts from the 3 selector duct studs projecting through dash. Remove screw attaching selector duct to dash. Pull selector duct rearward until heater core tubes clear the dash panel. Lower selector duct far enough to gain access to vacuum and electrical harnesses.
3. Disconnect vacuum and electrical harnesses. Remove selector duct assembly. Remove core mounting straps and core. To install, reverse removal procedure and adjust temperature control cable.

A/C-Heater Vacuum Diagram ("C" & "K" Series). Scheme 6

A/C-Heater Vacuum Diagram (All Other Models). Scheme 7

A/C-Heater Wiring Diagram ("C" & "K" Series). Scheme 8

Auxiliary A/C-Heater Wiring Diagram ("K"). Scheme 9