Heater Core; Expansion Valve; Blower Motor; Thermostatic Cycling Switch - Hummer H1 Service Manual

11-38 Heating/Ventilation/Air Conditioning (HVAC)

Heater Core

The heater core is composed of copper and brass with numer-
ous passages allowing heated engine coolant to pass through,
transferring heat into the passing air from the blower motor.
Coolant flow through the heater core is controlled by the water
control valve in the engine compartment (Figure 11-58).
RETAINING BRACKET
HEATER CORE
7-P11-004
Figure 11-58: Heater Core
Evaporator
The evaporator is composed of a wide flat aluminum tube bent
in a serpentine pattern. Fins extending out from the tube assist
in transferring heat from the passing air into the refrigerant
which is evaporating inside of the tubes (Figure 11-59).
THERMOSTATIC
CYCLING
SWITCH
HVAC CASE HALF (REAR)
Figure 11-59: Evaporator

Thermostatic Cycling Switch

The thermostatic cycling switch is mounted on the side of the
main HVAC unit (Figure 11-59). The thermostatic cycling
switch is responsible for turning off the compressor clutch
when evaporator temperature approaches freezing. Tempera-
ture is sensed by a capillary tube inserted in the fins of the
evaporator. Should the evaporator reach freezing temperatures,
moisture condensing on the fins of the evaporator will freeze
and hinder air flow. The thermostatic cycling switch will inter-
rupt current to the compressor clutch until the temperature rises
to about 40° F.
HVAC CASE HALF (FRONT)
EVAPORATOR
7-P11-004
______________________

Expansion Valve

The expansion valve controls the flow of refrigerant through
the evaporator. Refrigerant must be metered to prevent the liq-
uid refrigerant from flooding the evaporator. The expansion
valve is exposed to both low and high pressures, and bases re-
frigerant flow on the pressure which is exiting the evaporator
(Figure 11-60).
EXPANSION VALVE
Figure 11-60: Expansion Valve

Blower Motor

The blower motor is a permanent magnet electric motor that
drives a wheel type fan. The air enters the unit from the outside
air intake, or from a door on the interior of the vehicle. The air
is then forced through the evaporator and heater core.
BLOWER MOTOR
Figure 11-61: Blower Motor and Housing
Rear Defrost Button
The vehicle may be equipped with optional rear defrost. The
rear defrost is comprised of an electrical grid which is bonded
to the rear center glass. When the rear defrost button is pushed,
a timed electric current is sent to the grid causing the tempera-
ture of the grid and glass to slowly rise, melting frost or evapo-
rating exterior window fogging. The timer in the switch will
shut off the current when an adequate amount of time has
passed. This option is only available on the XLC2, and HMC4.
OUTLET
INLET
7-S11-061
BLOWER HOUSING
7-P11-003.1
®