Heating System; Heater And Defroster Operation - Jeep 1987 Wrangler Workshop Manual

HEATING AND AIR CONDITIONING
HEATING SYSTEM
GENERAL
A blend-air heating system is used in
Wrangler/YJ vehicles. The blend-air system pro-
vides a constant flow of engine coolant through
the heater core.
The temperature of heated air entering the
passenger compartment is controlled by
regulating the quantity of air flow through the
heater core. This is accomplished by blending
a controlled amount of unheated air from out-
side the vehicle with heated air from the heater
core.
HEATER AND DEFROSTER OPERATION
The heater core is connected to the engine
cooling system. It operates on the circulation
of heated engine coolant through the core and
a supply of fresh air drawn in through the in-
take grille on the cowl. Engine coolant flows
through the heater core at all times.
The heater controls are on the heater control
panel (1).
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The air control lever (2) operates a door in the
fresh air intake duct. The door controls the
amount of fresh air flow into the heater hous-
ing and core. When the lever is in the Off posi-
tion, the intake door is closed preventing air
flow into the housing.
The temperature control lever (3) determines air
flow through the heater core. The lever operates
the heater housing blend-air door which con-
trols air flow through the core.
The blower motor is operated by the control
switch (4). The switch provides three biower
speeds for increased air flow in heat or defrost
mode.
Heating
Maximum air flow and heater output occurs
when the air control lever (2) is in Heat posi-
tion and the temperature control lever (3) in
Warm position. The blend-air door is closed and
all intake air is directed through the core in this
operating mode.
Temperature regulation of the heated air is
determined by position of the temperature con-
trol lever (3). Moving the control lever from Warm
to an in-between position, opens the blend-air
door in the heater housing. As the door opens,
unheated outside air is drawn into the system
and blended with heated air from the core.
Defrosting
The heater housing contains a defroster door
to divert heated air to the defroster duct and
windshield outlets. Defrost air flow is controll-
ed by the air control lever (2).
For defroster operation, the air control lever (2)
must be moved to the defrost detent. The de-
tent is identified by the defrost symbol on the
control panel. In this position, the defroster
door in the heater housing diverts all heated air
(from the core) to the defroster duct windshield
outlets.
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